p53 and its isoforms in DNA double-stranded break repair

p53 and its isoforms in DNA double-stranded break repair p53及其异构体在DNA双链断裂修复中的作用 first-author corresp ‡Corresponding Author ‡Corresponding Author †E-mail:chenjun2009@zju.edu.cn †E-mail:chenjun2009@zju.edu.cn chenjun2009@zju.edu.cn MOE Key Laboratory of Biosystems Homeostasis & Protection and Innovation Center for Cell Signaling Network, College of Life Sciences, Zhejiang University, Hangzhou 310058, China MOE Key Laboratory of Biosystems Homeostasis & Protection and Innovation Center for Cell Signaling Network, College of Life Sciences, Zhejiang University, Hangzhou 310058, China DNA double-stranded break (DSB) is one of the most catastrophic damages of genotoxic insult. Inappropriate repair of DNA DSBs results in the loss of genetic information, mutation, and the generation of harmful genomic rearrangements, which predisposes an organism to immunodeficiency, neurological damage, and cancer. The tumor repressor p53 plays a key role in DNA damage response, and has been found to be mutated in 50% of human cancer. p53, p63, and p73 are three members of the p53 gene family. Recent discoveries have shown that human p53 gene encodes at least 12 isoforms. Different p53 members and isoforms play various roles in orchestrating DNA damage response to maintain genomic integrity. This review briefly explores the functions of p53 and its isoforms in DNA DSB repair. DNA双链断裂是DNA损伤最严重的形式.如果DNA断裂不能正确修复,将会导致遗传物质的丢失、基因突变和染色体重排.这不仅会影响正常的发育和衰老过程,而且更严重的是基因组的不完整会导致人类容易患上免疫缺陷、神经系统紊乱和癌症等疾病.抑癌基因 p53 在DNA损伤反应中扮演着一个中心角色,超过50%以上的人类癌细胞中p53发生了变异.p53家族包括p53、p63和p73三个成员.近年来研究发现:人的 p53 基因最少编码12个异构体,这些异构体在DNA损伤反应中起着不同作用,并协同p53一起维持基因组DNA的完整性.本综述将探讨p53及其异构体在DNA双链断裂修复中的作用. p53 p53 isoform DNA double-stranded break repair Cell death p53 p53异构体 DNA双链断裂修复 细胞死亡 Introduction 1 Cells are under a wide range of DNA damage pressures from both endogenous and exogenous sources. More than 1×10 4 DNA lesions occur in any given cell each day. To minimize the effects of toxic insults on their DNA, cells have evolved different mechanisms for tolerating, reversing, and repairing genomic insults. The most deleterious lesion in DNA is the double-stranded break (DSB). DNA DSB can be generated in a variety of ways, such as replication, reactive oxygen species (ROS) produced during metabolic processes, normal programmed genomic rearrangements including V(D)J recombination and mitotic or meiotic recombination, ionizing radiation, and chemical drugs like camptothecin. The failure in repairing DNA DSBs can lead to loss of chromosomes. Improper repair results in mutations and chromosome rearrangement (Dudáš and Chovanec, 2004 2004 ). To combat the threat of DNA DSBs, organisms have developed essentially three mechanisms for their repair, non-homologous end-joining (NHEJ), homologous recombination (HR), and single-stranded annealing (SSA) (Hakem, 2008 2008 ; Hiom, 2010 2010 ). Following DSB formation, the broken ends regardless of the genetic sequence at the breaks are processed to yield appropriate substrates for direct ligation. This process is called NHEJ and is initiated by the binding of Ku70/80 with the broken ends (Hiom, 2010 2010 ). Then, the Ku70/80 recruits downstream factors including DNA-dependent protein kinase catalytic subunit (DNA-PKcs) and Artemis. Finally the broken ends are ligated by the X-ray repair cross complementing 4 (XRCC4)-Ligase IV (LIG4) complex. NHEJ is the most straightforward way to repair a DSB and functions throughout the G1, S, and G2 phases of the cell cycle. However, if, as is often the case, nucleotides at the broken ends have been trimmed by nucleases or filled in by polymerases before the ligation, then small deletions and insertions are created. Therefore, NHEJ is considered to be error-prone. When cells progress through the S phase and into the G2 phase, a sister chromatid is produced by replication, one which provides a template for faithfully repairing the DNA DSBs by HR repair (Dudáš and Chovanec, 2004 2004 ). To initiate HR repair, double-stranded DNA (dsDNA) ends are exonucleolytically resected to form 3' single-stranded DNA (ssDNA) tails which are bound and stabilized by the single-stranded binding protein, replication protein A (RPA). With the help of RAD52 and BRCA2, RAD51 recombinase replaces RPA to assemble a nucleoprotein filament along the ssDNA tail. This filament initiates the search for homology in the sister chromatid and invades homologous intact sequences to form heteroduplex DNA. The missing sequence at the DSB site is restored by DNA synthesis. The two sister chromatids can exchange strands to form a Holliday junction. Finally, the Holliday junction is resolved and DNA is ligated. Thus, the genetic information lost at a break in one chromatid is accurately restored by HR repair. Unlike NHEJ, HR repair is error-free. In SSA repair, the DSB site consists of direct repeats (Dudáš and Chovanec, 2004 2004 ). The 3'-ssDNA tails are generated. The repeated sequences at 3'-ssDNA tails are aligned. Finally, the intervening sequences and protruding 3'-ends are removed by the endonuclease Ercc1-XPF. SSA repair does not require RAD51 but relies on RAD52, which facilitates pairing of the processed ssDNA tails before removal of the protruding 3'-ends. The most important part of the DNA damage response is the activation of tumor repressor p53 (Levine and Oren, 2009 2009 ). In response to different types and levels of stresses, p53 can be differentially activated by change in its stabilities and modifications. This results in various cellular events such as cell cycle arrest, DNA-damage repair, apoptosis and/or senescence to ensure genome integrity (Dai and Gu, 2010 2010 ). Interestingly, p53 protein appears to promote only some DNA-damage repair pathways, such as base excision repair, mismatch repair, and nucleotide excision repair (Gatz and Wiesmuller, 2006 2006 ; Helton and Chen, 2007 2007 ; Meek, 2009 2009 ), but inhibits DNA DSB repair pathways, including the HR, NHEJ, and SSA pathways (Mekeel et al., 1997 1997 ; Akyüz et al., 2002 2002 ; Keimling and Wiesmuller, 2009 2009 ). This phenomenon seems to be contradictory to its role as a “tumor repressor.” A large number of p53 isoforms have been identified in recent years (Courtois et al., 2002 2002 ; Bourdon et al., 2005 2005 ; Chen et al., 2009 2009 ). These p53 isoforms can either synergistically promote or antagonistically inhibit p53 functions, depending on the isoform structures and the target genes affected. This review will mainly focus on how p53 isoform Δ133p53 switches p53 signal from repressing to promoting DNA DSB repair. p53 and its isoforms 1 The full-length p53 protein is a transcription factor and consists of a transactivation domain (TAD), a proline-rich domain (PRD), a DNA-binding domain (DBD), a nuclear localization signal (NLS), an oligomerization domain (OD), and a C-terminal regulatory domain (CTD) (Okorokov and Orlova, 2009 2009 ), as shown in Fig. 1 1 . Under normal conditions, p53 protein remains at low levels. However, it can be activated by a wide variety of stress signals such as DNA damage, starvation, hypoxia, heat/cold shock, oncogene activation, developmental stress, etc. (Vogelstein et al., 2000 2000 ; Levine et al., 2006 2006 ). In response to a stress signal, the activation of p53 can be achieved by a series of post-translational modifications that include phosphorylation, acetylation, methylation, sumoylation, neddylation, and non-proteolytic mono-ubiquitylation (Pietsch et al., 2008 2008 ). Activated p53 binds to p53 responsive elements (REs) in the promoter regions to induce or repress the expression of its target genes. Usually, the p53 REs are found within a few thousand base pairs from the transcriptional start site of its target genes. There are two types of p53 REs. The first is composed of two pairs (half-sites) of pentamers arranged head-to-head, 5'-RRRC(A/T)(A/T)GYYY-3' (R: purine; Y: pyrimidine), separated by 0–38 nucleotides in the promoters of activated downstream genes, and the second type contains two pairs of pentamers arranged end-to-head, 5'-RRRC(A/T)(N)RRRC(A/T)-3' or 5'-(A/T)GYYY (N)(A/T)GYYY-3', separated by 0–13 nucleotides in the promoters of repressed downstream genes (Hoh et al., 2002 2002 ; Amson et al., 2011 2011 ). The biological roles of p53 downstream genes can be divided into three major groups: the negative regulators of p53 (mouse double minute protein 2 (MDM2), constitutive photomorphogenetic 1 (COP1), and p53-induced-RING-H2 (PIRH-2), etc.), the negative regulators of the cell cycle (p21, 14-3-3δ, and growth arrest and DNA damage 45 (GADD-45), etc.), and the apoptotic factors (BAX, p53-upregulated modulator of apoptosis (PUMA), NOXA, and DR, etc.). Activation of p53 leads to two cellular events, either cell cycle arrest to allow the repair of the damage or apoptosis in cells where the damage cannot be fixed. In addition to its transcription activity, p53 can also function in cytoplasm by directly interacting with anti-apoptotic proteins such as Bcl-2 and Bcl-XL in mitochondria, acting in a way similar to the so-called BH3 only protein (PUMA) (Chipuk et al., 2005 2005 ; Moll et al., 2005 2005 ). The MDM2 and the protein p14ARF are the main players of the p53 pathway (de Oca Luna et al., 1995 1995 ; Langheinrich et al., 2002 2002 ). The MDM2 is an E3 ligase which ubiquitylates p53 and targets it for proteasomal degradation, whereas p14ARF inhibits MDM2 and raises p53 levels. Human p53 gene has 11 exons and can create at least 12 different isoform proteins (Fig. 1 1 ) using multiple promoters, alternative splicing, and the internal ribosome entry site (IRES) (Joruiz and Bourdon, 2016 2016 ; Vieler and Sanyal, 2018 2018 ). The usage of the promoter (P1) leads to the production of p53 and Δ40p53 isoforms, whereas the internal promoter regulates the expression of Δ133p53 and Δ160p53 isoforms. The C-terminal isoforms β and γ can be produced by the alternative splicing of the intron 9 (Fig. 1a 1a ). p53β and p53γ 2 There are three C-terminal isoforms α, β, and γ. The α-isoform denotes full-length p53 of C-terminal and α is usually omitted. The β and γ isoforms lack the OD and CTD (Fig. 1b 1b ). However, p53β can form a complex with full-length p53 and selectively enhance p53 transcriptional activity at the BAX promoter, but not at the p21 promoter, thus driving the cell fate preferentially to apoptosis in response to stress conditions (Bourdon et al., 2005 2005 ). In normal culture or physiological conditions, p53β can also coordinate with p53 to accelerate replicative cellular senescence through upregulating the expression of microRNA-34a ( miR-34a ) (Fujita et al., 2009 2009 ; Mondal et al., 2013 2013 ). p53γ protein is unstable and localizes in either the nucleus of most cells or the cytoplasm of some cells. It has been observed that both β and γ isoforms were abnormally distributed in different cancer tissues (Anensen et al., 2006 2006 ). Δ40p53 2 Δ40p53 isoforms (also named p47 or ΔNp53) can be produced from P1 or P1' promoters. The Δ40p53 protein is an N-terminal truncated protein with a partial deletion in the TAD due to alternative splicing of exon 2 and/or alternative initiation of translation at ATG-40 (Fig. 1b 1b ). The deleted part of the TAD contains major activating phosphorylation sites and the MDM2-interacting motif. Because of the absence of MDM2-binding motif, Δ40p53 protein does not interact with MDM2 and therefore escapes the rapid degradation mechanism that regulates the full-length p53 level. Δ40p53 can regulate the function of p53 by oligomerizing with p53 in vivo (Courtois et al., 2002 2002 ). Unlike p53, as Δ40p53 has a truncated TAD, it is capable of inducing a different set of p53-responsive genes. It can induce many apoptosis-associated genes such as p53-induced protein with a death domain (PIDD), but repress cell cycle arrest genes such as p21 (Ohki et al., 2007 2007 ). In addition, Δ40p53 has a stronger tendency to form oligomers than p53 (Powell et al., 2008 2008 ), which results in dosage effects of Δ40p53 expression. Low levels of Δ40p53 can synergistically promote the transactivation activity of p53, whereas high levels of Δ40p53 induce a different set of genes (Powell et al., 2008 2008 ). Δ133p53 2 The Δ133p53 is transcribed from intron 4 (Fig. 1a 1a ) and conserved in zebrafish, Drosophila, and the mouse (Bourdon et al., 2005 2005 ; Chen et al., 2005 2005 ). This evolutionary conservation indicates the importance of the isoforms in the p53 signal pathway. The isoform Δ133p53 lacks 132 amino acids from the N-terminal of p53, which contains both the MDM2-interacting motif and the TAD and part of the DBD (Fig. 1b 1b ). Therefore, Δ133p53 imposes a more drastic effect on the p53 signal pathway. In response to both developmental and DNA damage stresses, Δ133p53 is directly transactivated by full-length p53 (Chen et al., 2009 2009 ; Marcel et al., 2010b 2010b ; Aoubala et al., 2011 2011 ). In turn, Δ133p53 inhibits p53-dependent apoptosis and G1 arrest without inhibiting p53-dependent G2 arrest by differentially modulating the expression of p53 target genes. Δ133p53 can form a complex with p53 both in vitro and in vivo. The anti-apoptotic activity of zebrafish Δ113p53, a Δ133p53 orthologue, is dependent on interacting with p53 (Ou et al., 2014 2014 ). Basal Δ133p53 expression can inhibit p53-mediated replicative senescence in normal human fibroblasts, T-lymphocytes and astrocytes by repressing miR-34a expression (Fujita et al., 2009 2009 ; Mondal et al., 2013 2013 ). Δ133p53 has been found to be overexpressed in some cancer cells. This promotes angiogenesis and tumor progression (Bernard et al., 2013 2013 ). Interestingly, under conditions of sub-toxic ROS stress, Δ133p53 does not antagonize the activity of full-length p53, but coordinates with p53 to promote cell survival by promoting antioxidant gene expression (Gong et al., 2016 2016 ). Δ133p53β can promote cancer stem cell potential by stimulating the expression of the key pluripotency factors SOX2 , OCT3/4 , and NANOG (Arsic et al., 2015 2015 ). (a) Diagram of human p53 gene structure. Alternative promoters (P1, P1', and P2) and alternative splicing sites (β, γ) are indicated. (b) p53 protein isoforms. TAD: transactivation domain; PXXP: proline-rich domain; DBD: DNA-binding domain; NLS: nuclear localization signal; OD: oligomerization domain; CTD: C-terminal regulatory domain Δ160p53 2 Like Δ133p53, Δ160p53 isoform is also translated from Δ133p53 transcript through the alternative translation start codon at Met160 (Fig. 1b 1b ) (Marcel et al., 2010a 2010a ). Δ160p53 may have a function similar to mutant p53s due to the lack of a major part of the DNA-binding domain. It has been reported that cells carrying p53 mutations, such as R175H or R248Q that are frequently found in human cancers, overexpress Δ160p53 isoform (Candeias et al., 2016 2016 ). Downregulation of Δ160p53 impairs the “gain-of-function” cancer phenotypes induced by mutant p53, suggesting that the Δ160p53 isoform possesses pro-oncogenic potential. p53 family members 1 The p53 family has three members, p53, p63, and p73. All encode a number of isoforms and share a high level of protein sequence similarity, particularly in the DNA-binding domain. Thus, p63 and p73 can transcribe p53 target genes causing cell cycle arrest and apoptosis (Bourdon, 2007 2007 ). However, p53, p63, and p73 are not entirely functionally redundant, as they exhibit promoter selectivity and have a number of unique target genes. The distinct functions of three genes have been demonstrated by studies on knockout mice. p53 knockout mice are viable and develop normally, but grow a tumor at a later stage (Donehower et al., 1992 1992 ). p63 null mice die a few days after birth and display severe developmental defects, including failure to develop limbs, skin, and other epithelial tissues (Mills et al., 1999 1999 ). Knockout of p73 results in infertility, spontaneous and carcinogen-induced tumorigenesis, as well as hippocampal dysgenesis (Yang et al., 2000 2000 ; Tomasini et al., 2008 2008 ; Wilhelm et al., 2010 2010 ). These results suggest that p53 mainly functions in DNA damage response and p63 plays a key role in development, whereas p73 is involved in both processes of DNA damage response and development. p53 in DNA DSB repair 1 An abundance of evidence has demonstrated that full-length p53 counteracts DNA DSB repair. Using three enhanced green fluorescent protein (EGFP)-based DNA DSB repair test systems, two studies showed that p53 plays a role in restraining three DNA DSB repair pathways including HR, NHEJ, and SSA (Akyüz et al., 2002 2002 ; Keimling and Wiesmuller, 2009 2009 ). More evidence revealed that p53 has direct regulatory activity in DNA DSB repair, as mutations in p53 that impair or even abolish its transcriptional activity and cell cycle regulatory capacity, and do not significantly affect its inhibition of HR (Willers et al., 2000 2000 ; Boehden et al., 2003 2003 ; Linke et al., 2003 2003 ). Protein association studies showed that p53 can form complexes with a number of HR components such as RAD51 (Buchhop et al., 1997 1997 ; Linke et al., 2003 2003 ), RPA (Romanova et al., 2004 2004 ), RAD54 (Linke et al., 2003 2003 ), BRCA1 (Zhang et al., 1998 1998 ), BRCA2 (Marmorstein et al., 1998 1998 ), BLM (Wang et al., 2001 2001 ), and WRN (Blander et al., 1999 1999 ). The interaction between p53 and either RAD51 or RAD54 inhibits HR repair by interrupting RAD51 polymerization and RAD51-mediated strand exchange (Yoon et al., 2004 2004 ). p53 modulates the helicase activities of BLM and WRN to counteract Holliday junction unwinding. The interaction of p53 with RPA mediates suppression of HR repair. p53 can also regulate HR repair at the transcription level through repressing the expression of RAD51 , RECQ4 , and WRN (Arias-Lopez et al., 2006 2006 ; Gatz and Wiesmuller, 2006 2006 ). p53 protein rapidly accumulates to a high level in response to DNA DSB stress at an early stage. However, activated p53 also activates the expression of MDM2, an E3 ligase that mediates the degradation of p53 in the later stage. Therefore, it is of great interest to understand the role of p53 signal pathway in response to DNA DSB stress in the later stage. Δ133p53 and p73 in DNA DSB repair 1 The restraining role of p53 in DNA DSB repair had remained elusive for many years until our recent discoveries demonstrated that Δ113p53/Δ133p53 functions to promote DNA DSB repair in 2015 and 2018 (Gong L et al., 2015 2015 ; Gong HJ et al., 2018 2018 ). In 2005, Δ133p53 and its zebrafish orthologous Δ113p53 were first identified in two reports, one on analysis of 5'-rapid amplification of cDNA end (RACE) polymerase chain reaction (PCR) products of p53 transcripts in human normal tissues (Bourdon et al., 2005 2005 ) and the other done by us on analysis of a zebrafish genetic mutant def hi429 (Chen et al., 2005 2005 ). Our following investigation discovered that Δ113p53 was strongly induced in response to DNA damage such as γ-irradiation and DNA damage drugs, camptothecin and roscovitine. More importantly, we found that Δ113p53 is a p53 target gene and functions to antagonize p53-mediated apoptosis (Chen et al., 2009 2009 ). As Δ113p53 is a p53 target gene, we were wondering what functions of Δ113p53 are in other stress conditions. To our surprise, both human Δ133p53 and zebrafish Δ113p53 were strongly induced by γ-irradiation, but not by ultraviolet (UV) irradiation or heat shock treatment; in contrast, full-length p53 was activated by all three treatments (Gong et al., 2015 2015 ). Protein analysis from both human cells and zebrafish showed that full-length p53 protein accumulated to the highest level as early as 4 h post irradiation (hpi), whereas Δ113p53 protein peaked later, at 24 hpi upon γ-irradiation. The result suggested that Δ113p53/Δ133p53 may play a role in DNA DSB repair. Using three EGFP-repairing-aided visual-cum-quantitative analysis reporter systems, we found that Δ113p53/Δ133p53 promoted all three DNA DSB repair pathways, including HR, NHEJ, and SSA, in a p53-independent manner. The positive role of Δ113p53/Δ133p53 on the DNA DSB repair was confirmed by analysis on DNA damage extents and repair foci of genomic DNA upon γ-irradiation. Interestingly, apoptotic activity was correlated positively with the level of p53 protein and negatively with the level of Δ113p53 protein, whereas the DNA damage repair corresponded to the level of Δ113p53 protein in γ-irradiated zebrafish embryos. Through deleting one of p53 REs in the P2 promoter, we generated a zebrafish Δ113p53 knockout mutant ( Δ113p53 M/M ). The expression of Δ113p53 was completely blocked in the mutant, but the activation of full-length p53 was not affected. In normal conditions, the mutant did not show any effects. However, the Δ113p53 M/M mutant embryos were more sensitive to γ-irradiation due to accumulating higher level of DNA damage extents and apoptotic cells. The significance of Δ113p53 in DNA DSB repair was further evaluated by blocking apoptosis with the overexpression of bcl2L (anti-apoptotic protein) in the irradiated mutant embryos. Blocking apoptosis with bcl2L significantly increased embryo viabilities in both wild type (WT) and Δ113p53 M/M upon γ-irradiation, whereas the difference of viability between WT and Δ113p53 M/M embryos still remained. The data from human cells also showed that knockdown of Δ133p53 coupled with γ-irradiation increased DNA damage and resulted in cell growth arrest at the G2 phase that in turn enhanced cell senescence at the later stage. Therefore, we demonstrated that both functions of Δ113p53/Δ133p53 in antagonizing apoptosis and promoting DNA DSB repair are important for its pro-survival characters upon DNA damage stress (Gong et al., 2015 2015 ). Unlike full-length p53, Δ113p53 does not form a complex with either Rad51 or Rpa. It promotes DNA DSB repair at the transcription level by enhancing the expression of the DNA DSB repair genes rad51 , lig4 , and rad52 , which is independent of full-length p53. Using promoter function analysis, gel shift and chromatin immunoprecipitation (ChIP) assays, we showed that Δ113p53 bound to a novel type of p53 RE in the promoters of three repair genes. Taken together, Δ113p53/Δ133p53 promotes DNA DSB repair via upregulating the expression of DNA DSB repair genes (Gong et al., 2015 2015 ). This finding raised a question on how Δ133p53, lacking the TAD, induces the transcription of these repair genes in a p53-independent manner. A previous ChIP-based analysis showed that p73 bound to the promoters of some DNA DSB repair genes, such as RAD51 , MRE11 , and BRCA2 . However, the overexpression of p73 did not greatly increase the expression of these genes (Lin et al., 2009 2009 ). These studies indicate that p73 plays a role in DNA DSB repair, which promotes us to investigate whether Δ133p53 coordinates with p73 to promote DNA DSB repair. As expected, we found that the expression of both p73 and Δ133p53 proteins increased to the highest level at 24 hpi and p73 formed a complex with Δ133p53, but not p53, after γ-irradiation (Gong et al., 2018 2018 ). Furthermore, through various methods, such as EGFP-repairing-aided visual-plus-quantitative analysis reporter systems, comet assays, and repair focal analyses, we demonstrated that Δ133p53 and p73 are interdependent in promoting all three DNA DSB repair pathways. ChIP assay showed that Δ133p53 promoted the binding of p73 to the promoters of the DNA DSB repair genes RAD51 , RAD52 , and LIG4 . This was required for p73 to transcribe the expression of the repair genes. Thus, p73 and Δ133p53 work together to ensure genomic integrity upon DNA DSBs (Gong et al., 2018 2018 ). In addition to the accumulation of p73 protein at 24 hpi, p73 also peaked as early as 4 hpi after γ-irradiation. Upon DNA damage, there are two mechanisms for p73 activation, one from protein phosphorylation by c-Ab1 tyrosine kinase (Gong et al., 1999 1999 ), and the other from upregulation of its messenger RNA (mRNA) expression by the transcription factor E2F1 (Irwin et al., 2000 2000 ; Gonzalez et al., 2003 2003 ). Our quantitative reverse-transcription PCR (qRT-PCR) results showed that p73 mRNA was upregulated at 12 hpi, but not before 4 hpi. The knockdown of c-Abl kinase resulted in a decrease of p73 protein at 4 hpi, but not at 24 hpi. More interestingly, when p73 was depleted upon γ-irradiation, apoptotic activity decreased only in the early stage (before 6 hpi), but not in the later stage (24 hpi), whereas DNA DSB accumulation was increased at 2 and 5 dpi (Gong et al., 2018 2018 ). These data illustrate that the first p73 protein peak results from protein stabilization with the aim of promoting apoptosis, whereas the second p73 protein peak is translated from increased mRNA to promote DNA damage repair. The finding suggests that both p73 functions in promoting apoptosis and DNA DSB repair are important for its tumor repressing role, which may explain the spontaneous and carcinogen-induced tumorigenesis observed in p73 knockout mice. A number of reports showed that the expression of Δ133p53 was elevated in different cancer tissues such as breast cancer, renal cell carcinoma, ovarian cancer, intrahepatic cholangiocarcinoma, colon cancer, and lung carcinoma (Bourdon et al., 2005 2005 ; Fujita et al., 2009 2009 ; Moore et al., 2010 2010 ; Nutthasirikul et al., 2013 2013 ; Kim and An, 2016 2016 ; Fragou et al., 2017 2017 ). This indicated that the upregulated Δ133p53 might be correlated with tumorigenesis because of its anti-apoptotic function or its role in promoting angiogenesis. There are a large number of somatic mutations in the promoter region of Δ133p53 in the COSMIC (Catalogue of Somatic Mutations in Cancer) cancer database. One of these mutated residues locates in exon 4. Interestingly, the mutations in this residue do not change the codon of full-length p53 protein. However, we found that the mutations attenuated the activation of Δ133p53 in response to the DNA damage (Gong et al., 2018 2018 ). Therefore, the loss of Δ133p53 function might be also associated with tumorigenesis because of its role in DNA damage repair. Model of p53 signal in DNA DSB repair 1 In summary, we propose a model to illustrate how the p53 signal protects genomic integrity upon ionizing irradiation (Fig. 2 2 ). At the early stage after irradiation, in cells with severe DNA damage, full-length p53 and p73 proteins are quickly stabilized to a high level, which inhibits DNA DSB repair and induces the expression of apoptotic genes, in turn to guide cells to undergo apoptosis. However, in cells with less and fixable DNA damage, p53 protein is activated at a relatively low level to transcribe its target genes such as MDM2 , p21 , and Δ133p53 , etc., while p73 mRNA is also transcribed by E2F1. The expression of MDM2 targets p53 protein for degradation, but not Δ133p53, due to Δ133p53 without MDM2-interacting motif. The cell cycle is arrested by the expression of negative regulators such as p21. Therefore, in the later stage, both p73 and Δ133p53 proteins can accumulate to higher levels, while p53 protein decreases to the basal level. The expression of Δ113p53 not only protects cells from death by its anti-apoptotic function, but also coordinates with p73 to transcribe repair genes to promote DNA DSB repair. Finally, genomic integrity is restored in survival cells. DSB: double-stranded break References N Akyüz , GS Boehden , S Süsse , 等 . DNA substrate dependence of p53-mediated regulation of double-strand break repair . Mol Cell Biol , 2002 . 22 ( 17 ): 6306 - 6317 . 12167722 DOI: 10.1128/MCB.22.17.6306-6317.2002 http://doi.org/10.1128/MCB.22.17.6306-6317.2002 . DNA substrate dependence of p53-mediated regulation of double-strand break repair R Amson , S Pece , A Lespagnol , 等 . Reciprocal repression between p53 and TCTP . Nat Med , 2011 . 18 ( 1 ): 91 - 99 . 22157679 DOI: 10.1038/nm.2546 http://doi.org/10.1038/nm.2546 . Reciprocal repression between p53 and TCTP N Anensen , AM Oyan , JC Bourdon , 等 . A distinct p53 protein isoform signature reflects the onset of induction chemotherapy for acute myeloid leukemia . Clin Cancer Res , 2006 . 12 ( 13 ): 3985 - 3992 . 16818696 DOI: 10.1158/1078-0432.CCR-05-1970 http://doi.org/10.1158/1078-0432.CCR-05-1970 . A distinct p53 protein isoform signature reflects the onset of induction chemotherapy for acute myeloid leukemia M Aoubala , F Murray-Zmijewski , MP Khoury , 等 . p53 directly transactivates Δ133p53 α , regulating cell fate outcome in response to DNA damage. C . ell Death Differ , 2011 . 18 ( 2 ): 248 - 258 . DOI: 10.1038/cdd.2010.91 http://doi.org/10.1038/cdd.2010.91 . p53 directly transactivates Δ133p53α, regulating cell fate outcome in response to DNA damage. C C Arias-Lopez , I Lazaro-Trueba , P Kerr , 等 . p53 modulates homologous recombination by transcriptional regulation of the RAD51 gene . EMBO Rep , 2006 . 7 ( 2 ): 219 - 224 . 16322760 DOI: 10.1038/sj.embor.7400587 http://doi.org/10.1038/sj.embor.7400587 . p53 modulates homologous recombination by transcriptional regulation of the RAD51 gene N Arsic , G Gadea , EL Lagerqvist , 等 . The p53 isoform Δ133p53β promotes cancer stem cell potential . Stem Cell Rep , 2015 . 4 ( 4 ): 531 - 540 . DOI: 10.1016/j.stemcr.2015.02.001 http://doi.org/10.1016/j.stemcr.2015.02.001 . The p53 isoform Δ133p53β promotes cancer stem cell potential H Bernard , B Garmy-Susini , N Ainaoui , 等 . The p53 isoform, Δ133p53α, stimulates angiogenesis and tumour progression . Oncogene , 2013 . 32 ( 17 ): 2150 - 2160 . 22733133 DOI: 10.1038/onc.2012.242 http://doi.org/10.1038/onc.2012.242 . The p53 isoform, Δ133p53α, stimulates angiogenesis and tumour progression G Blander , J Kipnis , JFM Leal , 等 . Physical and functional interaction between p53 and the Werner’s syndrome protein . J Biol Chem , 1999 . 274 ( 41 ): 29463 - 29469 . 10506209 DOI: 10.1074/jbc.274.41.29463 http://doi.org/10.1074/jbc.274.41.29463 . Physical and functional interaction between p53 and the Werner’s syndrome protein GS Boehden , N Akyüz , K Roemer , 等 . p53 mutated in the transactivation domain retains regulatory functions in homology-directed double-strand break repair . Oncogene , 2003 . 22 ( 26 ): 4111 - 4117 . 12821945 DOI: 10.1038/sj.onc.1206632 http://doi.org/10.1038/sj.onc.1206632 . p53 mutated in the transactivation domain retains regulatory functions in homology-directed double-strand break repair JC Bourdon . p53 family isoforms . Curr Pharm Biotechnol , 2007 . 8 ( 6 ): 332 - 336 . 18289041 DOI: 10.2174/138920107783018444 http://doi.org/10.2174/138920107783018444 . p53 family isoforms JC Bourdon , K Fernandes , F Murray-Zmijewski , 等 . p53 isoforms can regulate p53 transcriptional activity . Genes Dev , 2005 . 19 ( 18 ): 2122 - 2137 . 16131611 DOI: 10.1101/gad.1339905 http://doi.org/10.1101/gad.1339905 . p53 isoforms can regulate p53 transcriptional activity S Buchhop , MK Gibson , XW Wang , 等 . Interaction of p53 with the human Rad51 protein . Nucleic Acids Res , 1997 . 25 ( 19 ): 3868 - 3874 . 9380510 DOI: 10.1093/nar/25.19.3868 http://doi.org/10.1093/nar/25.19.3868 . Interaction of p53 with the human Rad51 protein MM Candeias , M Hagiwara , M Matsuda . Cancer-specific mutations in p53 induce the translation of Δ160p53 promoting tumorigenesis . EMBO Rep , 2016 . 17 ( 11 ): 1542 - 1551 . 27702985 . Cancer-specific mutations in p53 induce the translation of Δ160p53 promoting tumorigenesis J Chen , H Ruan , SM Ng , 等 . Loss of function of def selectively up-regulates Δ 113p53 expression to arrest expansion growth of digestive organs in zebrafish . Genes Dev , 2005 . 19 ( 23 ): 2900 - 2911 . 16322560 DOI: 10.1101/gad.1366405 http://doi.org/10.1101/gad.1366405 . Loss of function of def selectively up-regulates Δ113p53 expression to arrest expansion growth of digestive organs in zebrafish J Chen , SM Ng , CQ Chang , 等 . p53 isoform Δ113p53 is a p53 target gene that antagonizes p53 apoptotic activity via BclxL activation in zebrafish . Genes Dev , 2009 . 23 ( 3 ): 278 - 290 . 19204115 DOI: 10.1101/gad.1761609 http://doi.org/10.1101/gad.1761609 . p53 isoform Δ113p53 is a p53 target gene that antagonizes p53 apoptotic activity via BclxL activation in zebrafish JE Chipuk , L Bouchier-Hayes , T Kuwana , 等 . PUMA couples the nuclear and cytoplasmic proapoptotic function of p53 . Science , 2005 . 309 ( 5741 ): 1732 - 1735 . 16151013 DOI: 10.1126/science.1114297 http://doi.org/10.1126/science.1114297 . PUMA couples the nuclear and cytoplasmic proapoptotic function of p53 S Courtois , G Verhaegh , S North , 等 . ΔN-p53, a natural isoform of p53 lacking the first transactivation domain, counteracts growth suppression by wild-type p53 . Oncogene , 2002 . 21 ( 44 ): 6722 - 6728 . 12360399 DOI: 10.1038/sj.onc.1205874 http://doi.org/10.1038/sj.onc.1205874 . ΔN-p53, a natural isoform of p53 lacking the first transactivation domain, counteracts growth suppression by wild-type p53 C Dai , W Gu . p53 post-translational modification: deregulated in tumorigenesis . Trends Mol Med , 2010 . 16 ( 11 ): 528 - 536 . 20932800 DOI: 10.1016/j.molmed.2010.09.002 http://doi.org/10.1016/j.molmed.2010.09.002 . p53 post-translational modification: deregulated in tumorigenesis RM de Oca Luna , DS Wagner , G Lozano . Rescue of early embryonic lethality in mdm2 -deficient mice by deletion of p53 . Nature , 1995 . 378 ( 6553 ): 203 - 206 . 7477326 DOI: 10.1038/378203a0 http://doi.org/10.1038/378203a0 . Rescue of early embryonic lethality in mdm2-deficient mice by deletion of p53 LA Donehower , M Harvey , BL Slagle , 等 . Mice deficient for p53 are developmentally normal but susceptible to spontaneous tumours . Nature , 1992 . 356 ( 6366 ): 215 - 221 . 1552940 DOI: 10.1038/356215a0 http://doi.org/10.1038/356215a0 . Mice deficient for p53 are developmentally normal but susceptible to spontaneous tumours A Dudáš , M Chovanec . DNA double-strand break repair by homologous recombination . Mutat Res , 2004 . 566 ( 2 ): 131 - 167 . 15164978 DOI: 10.1016/j.mrrev.2003.07.001 http://doi.org/10.1016/j.mrrev.2003.07.001 . DNA double-strand break repair by homologous recombination A Fragou , G Tzimagiorgis , C Karageorgopoulos , 等 . Increased Δ133p53 mRNA in lung carcinoma corresponds with reduction of p21 expression . Mol Med Rep , 2017 . 15 ( 4 ): 1455 - 1460 . 28260096 DOI: 10.3892/mmr.2017.6162 http://doi.org/10.3892/mmr.2017.6162 . Increased Δ133p53 mRNA in lung carcinoma corresponds with reduction of p21 expression K Fujita , AM Mondal , I Horikawa , 等 . p53 isoforms Δ133p53 and p53β are endogenous regulators of replicative cellular senescence . Nat Cell Biol , 2009 . 11 ( 9 ): 1135 - 1142 . 19701195 DOI: 10.1038/ncb1928 http://doi.org/10.1038/ncb1928 . p53 isoforms Δ133p53 and p53β are endogenous regulators of replicative cellular senescence SA Gatz , L Wiesmuller . p53 in recombination and repair . Cell Death Differ , 2006 . 13 ( 6 ): 1003 - 1016 . 16543940 DOI: 10.1038/sj.cdd.4401903 http://doi.org/10.1038/sj.cdd.4401903 . p53 in recombination and repair HJ Gong , YX Zhang , KP Jiang , 等 . p73 coordinates with Δ133p53 to promote DNA double-strand break repair . Cell Death Differ , 2018 . 25 ( 6 ): 1063 - 1079 . 29511339 DOI: 10.1038/s41418-018-0085-8 http://doi.org/10.1038/s41418-018-0085-8 . p73 coordinates with Δ133p53 to promote DNA double-strand break repair JG Gong , A Costanzo , HQ Yang , 等 . The tyrosine kinase c-Abl regulates p73 in apoptotic response to cisplatin-induced DNA damage . Nature , 1999 . 399 ( 6738 ): 806 - 809 . 10391249 DOI: 10.1038/21690 http://doi.org/10.1038/21690 . The tyrosine kinase c-Abl regulates p73 in apoptotic response to cisplatin-induced DNA damage L Gong , HJ Gong , X Pan , 等 . p53 isoform Δ113p53/Δ133p53 promotes DNA double-strand break repair to protect cell from death and senescence in response to DNA damage . Cell Res , 2015 . 25 ( 3 ): 351 - 369 . 25698579 DOI: 10.1038/cr.2015.22 http://doi.org/10.1038/cr.2015.22 . p53 isoform Δ113p53/Δ133p53 promotes DNA double-strand break repair to protect cell from death and senescence in response to DNA damage L Gong , X Pan , ZM Yuan , 等 . p53 coordinates with Δ133p53 isoform to promote cell survival under low-level oxidative stress . J Mol Cell Biol , 2016 . 8 ( 1 ): 88 - 90 . 26705306 DOI: 10.1093/jmcb/mjv069 http://doi.org/10.1093/jmcb/mjv069 . p53 coordinates with Δ133p53 isoform to promote cell survival under low-level oxidative stress S Gonzalez , C Prives , C Cordon-Cardo . p73α regulation by Chk1 in response to DNA damage . Mol Cell Biol , 2003 . 23 ( 22 ): 8161 - 8171 . 14585975 DOI: 10.1128/MCB.23.22.8161-8171.2003 http://doi.org/10.1128/MCB.23.22.8161-8171.2003 . p73α regulation by Chk1 in response to DNA damage R Hakem . DNA-damage repair; the good, the bad, and the ugly . EMBO J , 2008 . 27 ( 4 ): 589 - 605 . 18285820 DOI: 10.1038/emboj.2008.15 http://doi.org/10.1038/emboj.2008.15 . DNA-damage repair; the good, the bad, and the ugly ES Helton , XB Chen . p53 modulation of the DNA damage response . J Cell Biochem , 2007 . 100 ( 4 ): 883 - 896 . 17031865 DOI: 10.1002/jcb.21091 http://doi.org/10.1002/jcb.21091 . p53 modulation of the DNA damage response K Hiom . Coping with DNA double strand breaks . DNA Repair , 2010 . 9 ( 12 ): 1256 - 1263 . 21115283 DOI: 10.1016/j.dnarep.2010.09.018 http://doi.org/10.1016/j.dnarep.2010.09.018 . Coping with DNA double strand breaks J Hoh , S Jin , T Parrado , 等 . The p53MH algorithm and its application in detecting p53-responsive genes . Proc Natl Acad Sci USA , 2002 . 99 ( 13 ): 8467 - 8472 . DOI: 10.1073/pnas.132268899 http://doi.org/10.1073/pnas.132268899 . The p53MH algorithm and its application in detecting p53-responsive genes M Irwin , MC Marin , AC Phillips , 等 . Role for the p53 homologue p73 in E2F-1-induced apoptosis . Nature , 2000 . 407 ( 6804 ): 645 - 648 . 11034215 DOI: 10.1038/35036614 http://doi.org/10.1038/35036614 . Role for the p53 homologue p73 in E2F-1-induced apoptosis SM Joruiz , JC Bourdon . p53 isoforms: key regulators of the cell fate decision . Cold Spring Harb Perspect Med , 2016 . 6 ( 8 ): a026039 26801896 DOI: 10.1101/cshperspect.a026039 http://doi.org/10.1101/cshperspect.a026039 . p53 isoforms: key regulators of the cell fate decision M Keimling , L Wiesmuller . DNA double-strand break repair activities in mammary epithelial cells–influence of endogenous p53 variants . Carcinogenesis , 2009 . 30 ( 7 ): 1260 - 1268 . 19429664 DOI: 10.1093/carcin/bgp117 http://doi.org/10.1093/carcin/bgp117 . DNA double-strand break repair activities in mammary epithelial cells–influence of endogenous p53 variants S Kim , SS An . Role of p53 isoforms and aggregations in cancer . Medicine (Baltimore) , 2016 . 95 ( 26 ): e3993 27368003 DOI: 10.1097/MD.0000000000003993 http://doi.org/10.1097/MD.0000000000003993 . Role of p53 isoforms and aggregations in cancer U Langheinrich , E Hennen , G Stott , 等 . Zebrafish as a model organism for the identification and characterization of drugs and genes affecting p53 signaling . Curr Biol , 2002 . 12 ( 23 ): 2023 - 2028 . 12477391 DOI: 10.1016/S0960-9822(02)01319-2 http://doi.org/10.1016/S0960-9822(02)01319-2 . Zebrafish as a model organism for the identification and characterization of drugs and genes affecting p53 signaling AJ Levine , M Oren . The first 30 years of p53: growing ever more complex . Nat Rev Cancer , 2009 . 9 ( 10 ): 749 - 758 . 19776744 DOI: 10.1038/nrc2723 http://doi.org/10.1038/nrc2723 . The first 30 years of p53: growing ever more complex AJ Levine , W Hu , Z Feng . The p53 pathway: what questions remain to be explored? . Cell Death Differ , 2006 . 13 ( 6 ): 1027 - 1036 . 16557269 DOI: 10.1038/sj.cdd.4401910 http://doi.org/10.1038/sj.cdd.4401910 . The p53 pathway: what questions remain to be explored? YL Lin , S Sengupta , K Gurdziel , 等 . p63 and p73 transcriptionally regulate genes involved in DNA repair . PLoS Genet , 2009 . 5 ( 10 ): e1000680 19816568 DOI: 10.1371/journal.pgen.1000680 http://doi.org/10.1371/journal.pgen.1000680 . p63 and p73 transcriptionally regulate genes involved in DNA repair SP Linke , S Sengupta , N Khabie , 等 . p53 interacts with hRAD51 and hRAD54, and directly modulates homologous recombination . Cancer Res , 2003 . 63 ( 10 ): 2596 - 2605 . 12750285 . p53 interacts with hRAD51 and hRAD54, and directly modulates homologous recombination V Marcel , S Perrier , M Aoubala , 等 . Δ160p53 is a novel N-terminal p53 isoform encoded by Δ133p53 transcript . FEBS Lett , 2010 . 584 ( 21 ): 4463 - 4468 . 20937277 DOI: 10.1016/j.febslet.2010.10.005 http://doi.org/10.1016/j.febslet.2010.10.005 . Δ160p53 is a novel N-terminal p53 isoform encoded by Δ133p53 transcript V Marcel , V Vijayakumar , L Fernández-Cuesta , 等 . p53 regulates the transcription of its delta133p53 isoform through specific response elements contained within the TP53 P2 internal promoter . Oncogene , 2010 . 29 ( 18 ): 2691 - 2700 . 20190805 DOI: 10.1038/onc.2010.26 http://doi.org/10.1038/onc.2010.26 . p53 regulates the transcription of its delta133p53 isoform through specific response elements contained within the TP53 P2 internal promoter LY Marmorstein , T Ouchi , SA Aaronson . The BRCA2 gene product functionally interacts with p53 and RAD51 . Proc Natl Acad Sci USA , 1998 . 95 ( 23 ): 13869 - 13874 . DOI: 10.1073/pnas.95.23.13869 http://doi.org/10.1073/pnas.95.23.13869 . The BRCA2 gene product functionally interacts with p53 and RAD51 DW Meek . Tumour suppression by p53: a role for the DNA damage response? . Nat Rev Cancer , 2009 . 9 ( 10 ): 714 - 723 . 19730431 DOI: 10.1038/nrc2716 http://doi.org/10.1038/nrc2716 . Tumour suppression by p53: a role for the DNA damage response? KL Mekeel , W Tang , LA Kachnic , 等 . Inactivation of p53 results in high rates of homologous recombination . Oncogene , 1997 . 14 ( 15 ): 1847 - 1857 . 9150391 DOI: 10.1038/sj.onc.1201143 http://doi.org/10.1038/sj.onc.1201143 . Inactivation of p53 results in high rates of homologous recombination AA Mills , BH Zheng , XJ Wang , 等 . p63 is a p53 homologue required for limb and epidermal morphogenesis . Nature , 1999 . 398 ( 6729 ): 708 - 713 . 10227293 DOI: 10.1038/19531 http://doi.org/10.1038/19531 . p63 is a p53 homologue required for limb and epidermal morphogenesis UM Moll , S Wolff , D Speidel , 等 . Transcription-independent pro-apoptotic functions of p53 . Curr Opin Cell Biol , 2005 . 17 ( 6 ): 631 - 636 . 16226451 DOI: 10.1016/j.ceb.2005.09.007 http://doi.org/10.1016/j.ceb.2005.09.007 . Transcription-independent pro-apoptotic functions of p53 AM Mondal , I Horikawa , SR Pine , 等 . p53 isoforms regulate aging-and tumor-associated replicative senescence in T lymphocytes . J Clin Invest , 2013 . 123 ( 12 ): 5247 - 5257 . 24231352 DOI: 10.1172/JCI70355 http://doi.org/10.1172/JCI70355 . p53 isoforms regulate aging-and tumor-associated replicative senescence in T lymphocytes HC Moore , LB Jordan , SE Bray , 等 . The RNA helicase p68 modulates expression and function of the Δ133 isoform(s) of p53, and is inversely associated with Δ133p53 expression in breast cancer . Oncogene , 2010 . 29 ( 49 ): 6475 - 6484 . 20818423 DOI: 10.1038/onc.2010.381 http://doi.org/10.1038/onc.2010.381 . The RNA helicase p68 modulates expression and function of the Δ133 isoform(s) of p53, and is inversely associated with Δ133p53 expression in breast cancer N Nutthasirikul , T Limpaiboon , C Leelayuwat , 等 . Ratio disruption of the Δ133p53 and TAp53 isoform equilibrium correlates with poor clinical outcome in intrahepatic cholangiocarcinoma . Int J Oncol , 2013 . 42 ( 4 ): 1181 - 1188 . 23404110 DOI: 10.3892/ijo.2013.1818 http://doi.org/10.3892/ijo.2013.1818 . Ratio disruption of the Δ133p53 and TAp53 isoform equilibrium correlates with poor clinical outcome in intrahepatic cholangiocarcinoma R Ohki , T Kawase , T Ohta , 等 . Dissecting functional roles of p53 N-terminal transactivation domains by microarray expression analysis . Cancer Sci , 2007 . 98 ( 2 ): 189 - 200 . 17233836 DOI: 10.1111/j.1349-7006.2006.00375.x http://doi.org/10.1111/j.1349-7006.2006.00375.x . Dissecting functional roles of p53 N-terminal transactivation domains by microarray expression analysis AL Okorokov , EV Orlova . Structural biology of the p53 tumour suppressor . Curr Opin Struct Biol , 2009 . 19 ( 2 ): 197 - 202 . 19286366 DOI: 10.1016/j.sbi.2009.02.003 http://doi.org/10.1016/j.sbi.2009.02.003 . Structural biology of the p53 tumour suppressor Z Ou , L Yin , CQ Chang , 等 . Protein interaction between p53 and Δ113p53 is required for the anti-apoptotic function of Δ113p53 . J Genet Genomics , 2014 . 41 ( 2 ): 53 - 62 . 24576456 DOI: 10.1016/j.jgg.2014.01.001 http://doi.org/10.1016/j.jgg.2014.01.001 . Protein interaction between p53 and Δ113p53 is required for the anti-apoptotic function of Δ113p53 EC Pietsch , SM Sykes , SB McMahon , 等 . The p53 family and programmed cell death . Oncogene , 2008 . 27 ( 50 ): 6507 - 6521 . 18955976 DOI: 10.1038/onc.2008.315 http://doi.org/10.1038/onc.2008.315 . The p53 family and programmed cell death DJ Powell , R Hrstka , M Candeias , 等 . Stress-dependent changes in the properties of p53 complexes by the alternative translation product p53/47 . Cell Cycle , 2008 . 7 ( 7 ): 950 - 959 . 18414054 DOI: 10.4161/cc.7.7.5626 http://doi.org/10.4161/cc.7.7.5626 . Stress-dependent changes in the properties of p53 complexes by the alternative translation product p53/47 LY Romanova , H Willers , MV Blagosklonny , 等 . The interaction of p53 with replication protein a mediates suppression of homologous recombination . Oncogene , 2004 . 23 ( 56 ): 9025 - 9033 . 15489903 DOI: 10.1038/sj.onc.1207982 http://doi.org/10.1038/sj.onc.1207982 . The interaction of p53 with replication protein a mediates suppression of homologous recombination R Tomasini , K Tsuchihara , M Wilhelm , 等 . TAp73 knockout shows genomic instability with infertility and tumor suppressor functions . Genes Dev , 2008 . 22 ( 19 ): 2677 - 2691 . 18805989 DOI: 10.1101/gad.1695308 http://doi.org/10.1101/gad.1695308 . TAp73 knockout shows genomic instability with infertility and tumor suppressor functions M Vieler , S Sanyal . p53 isoforms and their implications in cancer . Cancers , 2018 . 10 ( 9 ): 288 DOI: 10.3390/cancers10090288 http://doi.org/10.3390/cancers10090288 . p53 isoforms and their implications in cancer B Vogelstein , D Lane , AJ Levine . Surfing the p53 network . Nature , 2000 . 408 ( 6810 ): 307 - 310 . 11099028 DOI: 10.1038/35042675 http://doi.org/10.1038/35042675 . Surfing the p53 network XW Wang , A Tseng , NA Ellis , 等 . Functional interaction of p53 and BLM DNA helicase in apoptosis . J Biol Chem , 2001 . 276 ( 35 ): 32948 - 32955 . 11399766 DOI: 10.1074/jbc.M103298200 http://doi.org/10.1074/jbc.M103298200 . Functional interaction of p53 and BLM DNA helicase in apoptosis MT Wilhelm , A Rufini , MK Wetzel , 等 . Isoform-specific p73 knockout mice reveal a novel role for ΔNp73 in the DNA damage response pathway . Genes Dev , 2010 . 24 ( 6 ): 549 - 560 . 20194434 DOI: 10.1101/gad.1873910 http://doi.org/10.1101/gad.1873910 . Isoform-specific p73 knockout mice reveal a novel role for ΔNp73 in the DNA damage response pathway H Willers , EE McCarthy , B Wu , 等 . Dissociation of p53-mediated suppression of homologous recombination from G1/S cell cycle checkpoint control . Oncogene , 2000 . 19 ( 5 ): 632 - 639 . 10698508 DOI: 10.1038/sj.onc.1203142 http://doi.org/10.1038/sj.onc.1203142 . Dissociation of p53-mediated suppression of homologous recombination from G1/S cell cycle checkpoint control AN Yang , N Walker , R Bronson , 等 . p73-deficient mice have neurological, pheromonal and inflammatory defects but lack spontaneous tumours . Nature , 2000 . 404 ( 6773 ): 99 - 103 . 10716451 DOI: 10.1038/35003607 http://doi.org/10.1038/35003607 . p73-deficient mice have neurological, pheromonal and inflammatory defects but lack spontaneous tumours D Yoon , YZ Wang , K Stapleford , 等 . p53 inhibits strand exchange and replication fork regression promoted by human Rad51 . J Mol Biol , 2004 . 336 ( 3 ): 639 - 654 . 15095978 DOI: 10.1016/j.jmb.2003.12.050 http://doi.org/10.1016/j.jmb.2003.12.050 . p53 inhibits strand exchange and replication fork regression promoted by human Rad51 HB Zhang , K Somasundaram , Y Peng , 等 . BRCA1 physically associates with p53 and stimulates its transcriptional activity . Oncogene , 1998 . 16 ( 13 ): 1713 - 1721 . 9582019 DOI: 10.1038/sj.onc.1201932 http://doi.org/10.1038/sj.onc.1201932 . BRCA1 physically associates with p53 and stimulates its transcriptional activity Compliance with ethics guidelines Yu-xi ZHANG, Wen-ya PAN, and Jun CHEN declare that they have no conflict of interest. This article does not contain any studies with human or animal subjects performed by any of the authors. 10.1631/jzus.B1900167 Project supported by the National Natural Science Foundation of China (Nos. 31571511 and 31871500) 2019-03-31 2019-04-12 2022-01-05 Copyright © Zhejiang University and Springer-Verlag GmbH Germany, part of Springer Nature 2019 2019 Journal of Zhejiang University-SCIENCE B (Biomedicine and Biotechnology) 06 20