Member Of P53 Gene Family Research Articles

Drosophila p53 isoforms have overlapping and distinct functions in germline genome integrity and oocyte quality control.

p53 gene family members in humans and other organisms encode a large number of protein isoforms whose functions are largely undefined. Using Drosophila as a model, we find that a p53B isoform is expressed predominantly in the germline where it colocalizes with p53A into subnuclear bodies. It is only p53A, however, that mediates the apoptotic response to ionizing radiation in the germline and soma. In contrast, p53A and p53B are both required for the normal repair of meiotic DNA breaks, an activity that is more crucial when meiotic recombination is defective. We find that in oocytes with persistent DNA breaks p53A is also required to activate a meiotic pachytene checkpoint. Our findings indicate that Drosophila p53 isoforms have DNA lesion and cell type-specific functions, with parallels to the functions of mammalian p53 family members in the genotoxic stress response and oocyte quality control.

Oncogenic Intra-p53 Family Member Interactions in Human Cancers.

The p53 gene family members p53, p73, and p63 display several isoforms derived from the presence of internal promoters and alternative splicing events. They are structural homologs but hold peculiar functional properties. p53, p73, and p63 are tumor suppressor genes that promote differentiation, senescence, and apoptosis. p53, unlike p73 and p63, is frequently mutated in cancer often displaying oncogenic “gain of function” activities correlated with the induction of proliferation, invasion, chemoresistance, and genomic instability in cancer cells. These oncogenic functions are promoted either by the aberrant transcriptional cooperation of mutant p53 (mutp53) with transcription cofactors (e.g., NF-Y, E2F1, Vitamin D Receptor, Ets-1, NF-kB and YAP) or by the interaction with the p53 family members, p73 and p63, determining their functional inactivation. The instauration of these aberrant transcriptional networks leads to increased cell growth, low activation of DNA damage response pathways (DNA damage response and DNA double-strand breaks response), enhanced invasion, and high chemoresistance to different conventional chemotherapeutic treatments. Several studies have clearly shown that different cancers harboring mutant p53 proteins exhibit a poor prognosis when compared to those carrying wild-type p53 (wt-p53) protein. The interference of mutantp53/p73 and/or mutantp53/p63 interactions, thereby restoring p53, p73, and p63 tumor suppression functions, could be among the potential therapeutic strategies for the treatment of mutant p53 human cancers.

Hippo Component TAZ Functions as a Co-repressor and Negatively Regulates ΔNp63 Transcription through TEA Domain (TEAD) Transcription Factor

Transcriptional co-activator with a PDZ binding domain (TAZ) is a WW domain-containing transcriptional co-activator and a core component of an emerging Hippo signaling pathway that regulates organ size, tumorigenesis, metastasis, and drug resistance. TAZ regulates these biological functions by up-regulating downstream cellular genes through transactivation of transcription factors such as TEAD and TTF1. To understand the molecular mechanisms underlying TAZ-induced tumorigenesis, we have recently performed a gene expression profile analysis by overexpressing TAZ in mammary cells. In addition to the TAZ-up-regulated genes that were confirmed in our previous studies, we identified a large number of cellular genes that were down-regulated by TAZ. In this study, we have confirmed these down-regulated genes (including cytokines, chemokines, and p53 gene family members) as bona fide downstream transcriptional targets of TAZ. By using human breast and lung epithelial cells, we have further characterized ΔNp63, a p53 gene family member, and shown that TAZ suppresses ΔNp63 mRNA, protein expression, and promoter activity through interaction with the transcription factor TEAD. We also show that TEAD can inhibit ΔNp63 promoter activity and that TAZ can directly interact with ΔNp63 promoter-containing TEAD binding sites. Finally, we provide functional evidence that down-regulation of ΔNp63 by TAZ may play a role in regulating cell migration. Altogether, this study provides novel evidence that the Hippo component TAZ can function as a co-repressor and regulate biological functions by negatively regulating downstream cellular genes.

PP45 - Regulation of cell death signaling by sorafenib in hepatocellular carcinoma. role of p53 gene family members

PP45 - Regulation of cell death signaling by sorafenib in hepatocellular carcinoma. role of p53 gene family members

•Cellular functions of p53 and p53 gene family members p63 and p73

p53, hucre akibetinin belirlenmesinde onemli rol oynayan hucre dongusunun durdurulmasi veya programli hucre olumune yonlendirilmesi gibi hucresel bircok yolagin du­zenlenmesinde gorev alan bir transkripsiyon faktorudur. p53 araciligi ile programli hucre olumunun baslatilmasi veya hucre cogalmasinin durdurulmasi, hasarli DNA rep­likasyonunu ve genetik olarak normal olmayan hucrelerin cogalmasini engellemektedir. Bu nedenle p53 islevlerinin mutasyon ya da delesyon ile engellenmesi hucre home­ostasisin saglanmasinda da ayrica onemlidir. Bununla birlikte, calismalar p53\'ten yoksun farelerin ve Saos-2 gibi hucrelerin yasamlarini devam ettirebildiklerini gostermek­tedir. Bu durum, p53\'ten yoksun olan organizmalarda p53 islevini karsilayan p53-iliskili proteinlerin olabilecegini du­sundurmustur. p53 iliskili p63 ve p73 proteinlerinin kesfi, p53\'ten yoksun hucrelerde p53 bagimli genlerin transkrip­siyonlarina bir aciklama getirmistir. p63 ve p73 proteinle­rinin her ikisi de p53 proteini ile yuksek oranda benzerlik gostermekte ve p53\'un bazi islevlerini de paylasmaktadir­lar. p53\'ten farkli olarak p63 ve p73 insan kanserlerinde nadir olarak mutasyona ugramistir. Burada p53 hakkinda­ki guncel bilgilerle beraber p53-iliskili proteinler olan p63 ve p73 hakkindaki bilgileri de ozetlemeye calistik.

Identification of DeltaN Isoform and Polyadenylation Site Choice Variants in Molluscan p63/p73-Like Homologues

The p53 family of transcription factors has been implicated in many vertebrate cancers. Altered p53 and p73 protein expression observed in leukemic cells of molluscs suggests that these transcription factors might be involved in invertebrate cancers as well. Here, we fully characterize the mRNA of four novel p53-like variants in the bivalve molluscs Mytilus trossulus (bay mussel) and Mytilus edulis (blue mussel). These species, widely used for environmental assessment, develop a hemic neoplasia (leukemia) that is frequently fatal. The correlation between expression of p53 and its close relative p73 and onset of molluscan leukemia was documented previously. We report the sequences of two distinct and novel p63/p73-like mRNAs, amplified by polymerase chain reaction (PCR) from both species. One of the p63/p73-like isoforms contains a 360 nt truncation in the 5' coding region. Based on this truncation and concomitant lack of a transactivation (TA) domain, we designate this variant as a DeltaNp63/p73-like isoform: the first to be reported in an invertebrate species. In mammalian species, DeltaNp73 potently inhibits the tumor-suppressive function of p73 and p53, and its overexpression serves as a robust marker for mammalian cancer. In addition, we report on the occurrence of alternate polyadenylation sites in the molluscan p63/p73: one proximal and one distal site, which differ by 1260 nt. We hypothesize that differential expression of various molluscan p63/p73-like isoforms, controlled in part by polyadenylation site choice variation, may help to interpret the apparently opposing roles of this gene in the development of cancer. Overall, this research further illustrates the utility of the molluscan model for studies involving the molecular mechanisms of oncogenesis in naturally occurring populations. The data presented here require a revisiting of hypotheses regarding evolution of the p53 gene family. Current hypotheses indicate that (1) the protostome gene family does not contain an intronic promoter for DeltaN expression and (2) p53 gene duplication did not occur in protostomes. Our characterization of DeltaN p63/73 in mussel suggests that molluscan p53 gene family members have acquired an intronic promoter or splicing mechanism, either by invention that predates the evolutionary split of deuterostomes from protostomes, or by parallel evolution. Our data also show that Mytilus p53, p63/p73, and DeltaNp63/p73 are identical in their core regions with variation limited to their C- and N-terminals, supporting the notion that alternative splicing, intronic promoter usage, and polyadenylation site choice may lead to expression of distinct isoforms originating from one common gene.

P63 mediates survival in squamous cell carcinoma by suppression of p73-dependent apoptosis

We demonstrate that deltaNp63alpha is an essential survival factor in head and neck squamous cell carcinoma (HNSCC) through its ability to suppress p73-dependent apoptosis. Inhibition of endogenous p63 expression by RNAi induces apoptosis selectively in HNSCC cells that overexpress deltaNp63alpha. Knockdown of p63 induces the proapoptotic bcl-2 family members Puma and Noxa, and both their induction and subsequent cell death are p53 independent but require transactivating isoforms of p73. Inhibition of p73-dependent transcription by deltaNp63alpha involves both direct promoter binding and physical interaction with p73. In HNSCC cells lacking endogenous deltaNp63alpha expression, bcl-2 is instead upregulated and can suppress p73-mediated death. Together, these data define a pathway whereby deltaNp63alpha promotes survival in squamous epithelial malignancy by repressing a p73-dependent proapoptotic transcriptional program.

Different expressions of p53 gene family members and their clinical significance in human non-small cell lung cancer

To investigate the different expressions of p53 gene family members p53, p63 and p73, and their clinical significance in non small cell lung cancer (NSCLC). p53, p63 and p73 protein expressions were detected in 60 NSCLC tissues and 7 normal lung tissues by immunohistochemistry. In NSCLC, positive rate of p53, p63 and p73 protein was 61.67%(37/60), 80.00%(48/60), 73.33% (44/60) respectively. There were significant differences in positive rate of three proteins as compared to normal lung tissue ( P < 0.05). p53 protein expression was closely associated with tumor cell differentiation degree ( P =0.023), but was not associated with histological classification, lymph node metastasis and clinical stages ( P > 0.05). Expression of p63 protein was closely related to lymph node metastasis ( P =0.028) and histological classification ( P =0.001), but not to cell differentiation degree and clinical stages ( P > 0.05). There was no significant relationship between p73 protein expression and clinical characteristics of NSCLC ( P > 0.05). A positive correlation was present between p63 and p73 protein expressions ( P =0.000 1). No statistical correlation was found between p53 and p73 ( P > 0.05). p53 gene family may be related to the oncogenesis and development of NSCLC. p63 and p73 proteins may have different biological function from p53 protein, and both might play oncogenic roles.

P63/73 homologues in surf clam: novel signaling motifs and implications for control of expression

To understand the role of p53 gene family members during invertebrate embryonic development, we used polymerase chain reaction (PCR) to identify p63/73 homologues in the marine mollusc Spisula solidissima. Here, we report the sequences of two distinct p63/73-like homologues, both cloned from Spisula embryos. The first, Ssp63/73α is 2699 nucleotide (nt); the second, Spp63/73β is 3920 nt. The nucleotide sequences of the two variants are nearly identical up to their stop codons but diverge in their 3′-untranslated regions (UTRs). The deduced amino acid sequence of both Ssp63/73 variants is 597 amino acids, coding for a protein with predicted molecular weight of approximately 68 kDa. We conclude that the two unique transcripts, containing 3′ UTRs of variable lengths, represent tandem alternate polyadenylation sites for the Ssp63/73 gene. While alternative splicing has been well documented in the p63/73 gene family, this is the first report of alternate polyadenylation site choice as a control point for p63/73 gene expression in any species. In order to identify specific post-transcriptional as well as post-translational signals potentially involved in regulation of p63/73-like expression, we compared Ssp63/p73 nucleotide and Ssp63/73 deduced amino acid sequences to corresponding regions of other mammalian and nonmammalian p63 and p73 homologues. Within the Spisula 3′ UTRs we identified multiple AU-rich elements (AREs) which may control translation activation. Within the deduced amino acid sequence, we identified potential sites for sumoylation, a post-translational process that has been identified in mammalian p63 and p73 proteins. Identification of these novel signaling sites provides information about potential mechanisms controlling expression of multiple p63/73 isoforms during development.

Expression of p63 in the testis of mouse embryos.

Apoptosis of testicular germ cells during fetal development is regulated by both p53-dependent and independent mechanisms. However, its precise mechanisms are largely unknown. A member of p53 gene family, p63, is required for p53-dependent apoptosis and can induce apoptosis in the absence of p53 through the activation of p53-target genes. In this study, we examined the expression pattern of p63 in the mouse testis from embryonic day (E) 13.5 to E18.5 to clarify their possible role in the regulation of germ cell apoptosis. Immunostaining for p63 was found in the nucleus of germ cells at E13.5, and continuously observed until E18.5. The RT-PCR using specific primers for two p63 isotypes, those containing the transactivation domain and others not, showed that both transcripts were expressed in the fetal gonads. Possible roles of p63 in the embryonic testes were discussed.

Differential expression of p53 gene family members p63 and p73 in head and neck squamous tumorigenesis

p73 and p63 are recently cloned genes that share considerable structural and functional homologies with the p53 tumor suppressor gene. These genes, unlike p53, express multiple mRNA isoforms with variable biologic functions, and their suppressor nature has yet to be confirmed. To determine the interrelationship between these genes in the tumorigenesis of head and neck squamous carcinoma (HNSC), we performed immunohistochemical analyses of their protein products and compared the data with clinicopathologic parameters in 38 patients. In histologically normal epithelium, p53 and p73 showed similar basal and/or parabasal expression, but that of p53 was weaker and discontinuous. p63 staining was noted in more suprabasal cellular layers and was stronger. In dysplasias, all three markers manifested variable but gradual increase in extent and intensity of cellular expression with histologic progression. In carcinomas, p63 was the most frequently expressed (94.7%), followed by p73 (68.4%) and p53 (52.6%). Significant statistical correlation was noted only between p63 and p73 expressions (P =.04). Although no statistical correlation was found between p53 and p63 or p73, p53-negative tumors overexpressed either p63 or p73. p73 expression was associated with distant metastasis and perineural/vascular invasion. Our study indicates that (1) p63 and p73 expression may represent an early event in HNSC tumorigenesis, (2) the lack of correlation between p73 or p63 and p53 expression suggests an independent and/or compensatory functional role, (3) p73 expression may play a part in HNSC progression, and (4) p73 and p63 may function as oncogenes in the development of these tumors. HUM PATHOL 33:158-164. Copyright 2002, Elsevier Science (USA). All rights reserved.

Multiple protein differences distinguish clam leukemia cells from normal hemocytes: evidence for the involvement of p53 homologues

In coastal locations, marine invertebrates, primarily molluscs, develop fatal leukemias in their blood or hemolymph. In the clam Mya arenaria, non-adhesive, mitotic, spherical leukemia cells replace adhesive, motile, normal hemocytes as leukemia progresses. End-stage leukemia cells express a unique antigen, IE10, while normal cells express the 2A4 marker. The goals of this work were to further differentiate the normal and leukemia specific antigens relative to protein structure, determine if other protein distinctions exist, and examine p53 gene family expression in both cell types. Recognized by the monoclonal antibody 2A4, normal cells express a 185-kDa glycoprotein that may have multiple forms. Detected by the monoclonal antibody 1E10, leukemic cells express a very hydrophobic 252-kDa glycoprotein that is likely to be a transmembrane protein with spectrin/dystrophin-like characteristics. After normalization to the major cytoskeletal protein actin, sodium dodecyl sulfate-polyacrylamide gel electrophoresis reveals major distinguishing protein and glycoprotein differences between the two cell types. Most obvious is the near-absence of tubulin in the non-mitotic normal hemocytes. We have also characterized the expression of p53 gene family members in normal and end-stage leukemia cells, finding shifts in expression of the p53 gene homologues p73 and p97 coincident with leukemia-specific protein synthesis.