The transactivating isoforms of p63 are overexpressed in high-grade follicular lymphomas independent of the occurrence ofp63 gene amplification

Identification of a novel MEF2C::SS18L1 fusion in childhood acute B-lymphoblastic leukemia

PURPOSE

Leukemia-associated fusion genes are closely related to the occurrence, development, diagnosis, and treatment of leukemia. DNA microarrays and second-generation sequencing have discovered multiple B-ALL fusion genes. We identified a novel MEF2C::SS18L1 fusion gene in a child diagnosed with B-ALL. This study investigates the oncogenicity and prognosis of this fusion gene in B-ALL.

METHODS

A child with B-ALL who has a MEF2C::SS18L1 fusion is reported as a newly discovered case. Compared the breakpoints, structural domains, clinical phenotypes, and differential expression genes of MEF2C::SS18L1 and MEF2D::SS18.Using "ONCOFUSE" software, the carcinogenicity of MEF2C::SS18L1 is predicted. Using whole transcriptome sequencing, we analyze the breakpoints and the secondary structure of the fusion protein. Further, we compared the structures, differentially expressed genes, and clinical phenotypes of MEF2D and MEF2C fusion genes by DESeq, GO functional enrichment, and flow cytometry immunophenotyping analysis.

RESULTS

Whole transcriptome sequencing identified a MEF2C::SS18L1 fusion transcript in a 3-year-old child with B-ALL. The MADS box, MEF structural domain, HJURP_C structural domain, and TAD I structural domain of MEF2C, and the QPGY structural domain of SS18L1, make up the fusion protein. "Oncofuse" found a 0.99 Bayesian probability that the fusion gene drives cancer. The breakpoint positions, fusion protein secondary structures, differentially expressed genes, and clinical characteristics of this patient were identical to those with MEF2D::SS18 fusion gene.

CONCLUSION

We identified a novel MEF2C::SS18L1 fusion gene in childhood ALL, which shares similar structural and clinical characteristics with MEF2D::SS18. Further studies with more samples should be conducted in future.

DNA Demethylation Switches Oncogenic ΔNp63 to Tumor Suppressive TAp63 in Squamous Cell Carcinoma

The TP63 gene encodes two major protein variants; TAp63 contains a p53-like transcription domain and consequently has tumor suppressor activities whereas ΔNp63 lacks this domain and acts as an oncogene. The two variants show distinct expression patterns in normal tissues and tumors, with lymphocytes and lymphomas/leukemias expressing TAp63, and basal epithelial cells and some carcinomas expressing high levels of ΔNp63, most notably squamous cell carcinomas (SCC). Whilst the transcriptional functions of TAp63 and ΔNp63 isoforms are known, the mechanisms involved in their regulation are poorly understood. Using squamous epithelial cells that contain high levels of ΔNp63 and low/undetectable TAp63, the DNA demethylating agent decitabine (5-aza-2’-deoxycytidine, 5-dAza) caused a dose-dependent increase in TAp63, with a simultaneous reduction in ΔNp63, indicating DNA methylation-dependent regulation at the isoform-specific promoters. The basal cytokeratin KRT5, a direct ΔNp63 transcriptional target, was also reduced, confirming functional alteration of p63 activity after DNA demethylation. We also showed high level methylation of three CpG sites in the TAP63 promoter in these cells, which was reduced by decitabine. DNMT1 depletion using inducible shRNAs partially replicated these effects, including an increase in the ratio of TAP63:ΔNP63 mRNAs, a reduction in ΔNp63 protein and reduced KRT5 mRNA levels. Finally, high DNA methylation levels were found at the TAP63 promoter in clinical SCC samples and matched normal tissues. We conclude that DNA methylation at the TAP63 promoter normally silences transcription in squamous epithelial cells, indicating DNA methylation as a therapeutic approach to induce this tumor suppressor in cancer. That decitabine simultaneously reduced the oncogenic activity of ΔNp63 provides a “double whammy” for SCC and other p63-positive carcinomas. Whilst a variety of mechanisms may be involved in producing the opposite effects of DNA demethylation on TAp63 and ΔNp63, we propose an “either or” mechanism in which TAP63 transcription physically interferes with the ability to initiate transcription from the downstream ΔNP63 promoter on the same DNA strand. This mechanism can explain the observed inverse expression of p63 isoforms in normal cells and cancer.

The TΑp63/BCL2 Axis Represents A Novel Mechanism Of Clinical Aggressiveness In Chronic Lymphocytic Leukemia

High expression of TAp63 is linked to adverse clinical outcomes in CLL.

TAp63 contributes to the antiapoptotic phenotype of CLL cells, likely through modulating BCL2 protein expression.

The TA-isoform of the p63 transcription factor (TAp63) has been reported to contribute to clinical aggressiveness in chronic lymphocytic leukemia (CLL) in a hitherto elusive way. Here, we sought to further understand and define the role of TAp63 in the pathophysiology of CLL. First, we found that elevated TAp63 expression levels are linked with adverse clinical outcomes, including disease relapse and shorter time-to-first treatment and overall survival. Next, prompted by the fact that TAp63 participates in an NF-κB/TAp63/BCL2 antiapoptotic axis in activated mature, normal B cells, we explored molecular links between TAp63 and BCL2 also in CLL. We documented a strong correlation at both the protein and the messenger RNA (mRNA) levels, alluding to the potential prosurvival role of TAp63. This claim was supported by inducible downregulation of TAp63 expression in the MEC1 CLL cell line using clustered regularly interspaced short palindromic repeats (CRISPR) system, which resulted in downregulation of BCL2 expression. Next, using chromatin immunoprecipitation (ChIP) sequencing, we examined whether BCL2 might constitute a transcriptional target of TAp63 and identified a significant binding profile of TAp63 in the BCL2 gene locus, across a genomic region previously characterized as a super enhancer in CLL. Moreover, we identified high-confidence TAp63 binding regions in genes mainly implicated in immune response and DNA-damage procedures. Finally, we found that upregulated TAp63 expression levels render CLL cells less responsive to apoptosis induction with the BCL2 inhibitor venetoclax. On these grounds, TAp63 appears to act as a positive modulator of BCL2, hence contributing to the antiapoptotic phenotype that underlies clinical aggressiveness and treatment resistance in CLL.

p63 expression in human tumors and normal tissues: a tissue microarray study on 10,200 tumors

Background

Tumor protein 63 (p63) is a transcription factor of the p53 gene family involved in differentiation of several tissues including squamous epithelium. p63 immunohistochemistry is broadly used for tumor classification but published data on its expression in cancer is conflicting.

Methods

To comprehensively catalogue p63 expression, tissue microarrays (TMAs) containing 12,620 tissue samples from 115 tumor entities and 76 normal tissue types were analyzed.

Results

p63 expression was seen in various normal tissues including squamous epithelium and urothelium. At least occasional weak p63 positivity could be detected in 61 (53%) of 115 different tumor types. The frequencies of p63 positivity was highest in squamous cell carcinomas irrespective of their origin (96–100%), thymic tumors (100%), urothelial carcinomas (81–100%), basal type tumors such as basal cell carcinomas (100%), and various salivary gland neoplasias (81–100%). As a rule, p63 was mostly expressed in cancers derived from p63 positive normal tissues and mostly not detectable in tumors derived from p63 negative cancers. However, exceptions from this rule occurred. A positive p63 immunostaining in cancers derived from p63 negative tissues was unrelated to aggressive phenotype in 422 pancreatic cancers, 160 endometrium cancers and 374 ovarian cancers and might be caused by aberrant squamous differentiation or represent stem cell properties. In 355 gastric cancers, aberrant p63 expression occurred in 4% and was linked to lymph node metastasis (p = 0.0208). Loss of p63 in urothelial carcinomas - derived from p63 positive urothelium - was significantly linked to advanced stage, high grade (p < 0.0001 each) and poor survival (p < 0.0001) and might reflect clinically relevant tumor dedifferentiation.

Conclusion

The high prevalence of p63 expression in specific tumor types makes p63 immunohistochemistry a suitable diagnostic tool. Loss of p63 expression might constitute a feature of aggressive cancers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40364-021-00260-5.

An Algorithmic Immunohistochemical Approach to Define Tumor Type and Assign Site of Origin

Immunohistochemistry represents an indispensable complement to an epidemiology and morphology-driven approach to tumor diagnosis and site of origin assignment. This review reflects the state of my current practice, based on 15-years' experience in Pathology and a deep-dive into the literature, always striving to be better equipped to answer the age old questions, "What is it, and where is it from?" The tables and figures in this manuscript are the ones I "pull up on the computer" when I am teaching at the microscope and turn to myself when I am (frequently) stuck. This field is so exciting because I firmly believe that, through the application of next-generation immunohistochemistry, we can provide better answers than ever before. Specific topics covered in this review include (1) broad tumor classification and associated screening markers; (2) the role of cancer epidemiology in determining pretest probability; (3) broad-spectrum epithelial markers; (4) noncanonical expression of broad tumor class screening markers; (5) a morphologic pattern-based approach to poorly to undifferentiated malignant neoplasms; (6) a morphologic and immunohistochemical approach to define 4 main carcinoma types; (7) CK7/CK20 coordinate expression; (8) added value of semiquantitative immunohistochemical stain assessment; algorithmic immunohistochemical approaches to (9) "garden variety" adenocarcinomas presenting in the liver, (10) large polygonal cell adenocarcinomas, (11) the distinction of primary surface ovarian epithelial tumors with mucinous features from metastasis, (12) tumors presenting at alternative anatomic sites, (13) squamous cell carcinoma versus urothelial carcinoma, and neuroendocrine neoplasms, including (14) the distinction of pheochromocytoma/paraganglioma from well-differentiated neuroendocrine tumor, site of origin assignment in (15) well-differentiated neuroendocrine tumor and (16) poorly differentiated neuroendocrine carcinoma, and (17) the distinction of well-differentiated neuroendocrine tumor G3 from poorly differentiated neuroendocrine carcinoma; it concludes with (18) a discussion of diagnostic considerations in the broad-spectrum keratin/CD45/S-100-"triple-negative" neoplasm.

p63 expression in Merkel cell carcinoma: comparative immunohistochemistry invokes TAp63 as the dominant isoform involved

The literature suggests that p63 expression in Merkel cell carcinoma (MCC) is associated with a poor prognosis. p63 immunohistochemistry marks the 2 main isoforms of this transcriptional protein: TAp63 (tumor suppressor-like properties) and ∆Np63 (oncogenic properties). Little information about the isoform of relevance in MCC exists. p40 immunohistochemistry specifically marks ∆Np63, and using comparative, semiquantitative expression of p63 and p40, we sought to clarify the issue. Our cohort of 53 cases (28 men and 25 women, median age 79 years, interquartile range 71-88) was stratified by morphology and viral status. Immunohistochemistry (p63, p40, and cytokeratin 5/6) was performed, H-scores for nuclear expression of p63 and p40 were derived (2 observers; positivity ≥ 10), and interobserver agreement was evaluated. Clinical, pathological, and outcome data were documented. The results were analyzed statistically. Mortality amounted to 57% (median follow-up 686 days, interquartile range 292-1599). Positivity for Merkel cell polyomavirus was observed in 29 (55%) of cases. Expression of p63 and p40 was present in 36 (69%) and 4 (8%) of cases, respectively. Increased age (P = .0241), negative Merkel cell polyomavirus status (P = .0185), and p63 positivity (P = .0012) were significantly associated with mortality. The latter 2 variables were highly correlated (P = .004). The interclass correlation between the 2 sets of H-scores was 0.95. Our findings support an association between p63 expression and reduced overall survival in MCC and show consistency in scoring this prognostic parameter. TAp63 is the dominant isoform of the protein involved. The paradoxical tumor suppressor-like activity of this isoform in p63-positive MCCs with reduced overall survival requires further study.

A double dealing tale of p63: an oncogene or a tumor suppressor

As a member of tumor suppressor p53 family, p63, a gene encoding versatile protein variant, has been documented to correlate with cancer formation and progression, though it is rarely mutated in cancer patients. However, it has long been controversial on whether p63 is an oncogene or a tumor suppressor. Here, we comprehensively reviewed reports on roles of p63 in development, tumorigenesis and tumor progression. According to data from molecular cell biology, genetic models and clinic research, we conclude that p63 may act as either an oncogene or a tumor suppressor gene in different scenarios: TA isoforms of p63 gene are generally tumor-suppressive through repressing cell proliferation, survival and metastasis; ΔN isoforms, however, may initiate tumorigenesis via promoting cell proliferation and survival, but inhibit tumor metastasis and progression; effects of p63 on tumor formation and progression depend on the context of the whole p53 family, and either amplification or loss of p63 gene locus can break the balance to cause tumorigenesis.

p63 isoforms in triple-negative breast cancer: ΔNp63 associates with the basal phenotype whereas TAp63 associates with androgen receptor, lack of BRCA mutation, PTEN and improved survival

The TP63 gene encodes two major protein variants that differ in their N-terminal sequences and have opposing effects. In breast, ΔNp63 is expressed by immature stem/progenitor cells and mature myoepithelial/basal cells and is a characteristic feature of basal-like triple-negative breast cancers (TNBCs). The expression and potential role of TAp63 in the mammary gland and breast cancers is less clear, partly due to the lack of studies that employ p63 isoform-specific antibodies. We used immunohistochemistry with ΔNp63-specific or TAp63-specific monoclonal antibodies to investigate p63 isoforms in 236 TNBCs. TAp63, but not ΔNp63, was seen in tumour-associated lymphocytes and other stromal cells. Tumour cells showed nuclear staining for ΔNp63 in 17% of TNBCs compared to 7.3% that were positive for TAp63. Whilst most TAp63⁺ tumours also contained ΔNp63⁺ cells, the levels of the two isoforms were independent of each other. ΔNp63 associated with metaplastic and medullary cancers, and with a basal phenotype, whereas TAp63 associated with androgen receptor, BRCA1/2 wild-type status and PTEN positivity. Despite the proposed effects of p63 on proliferation, Ki67 did not correlate with either p63 isoform, nor did they associate with p53 mutation status. ΔNp63 showed no association with patient outcomes, whereas TAp63⁺ patients showed fewer recurrences and improved overall survival. These findings indicate that both major p63 protein isoforms are expressed in TNBCs with different tumour characteristics, indicating distinct functional activities of p63 variants in breast cancer. Analysis of individual p63 isoforms provides additional information into TNBC biology, with TAp63 expression indicating improved prognosis.

Acquired CYP19A1 amplification is an early specific mechanism of aromatase inhibitor resistance in ERα metastatic breast cancer

Tumor evolution is shaped by many variables, potentially involving external selective pressures induced by therapies. After surgery, patients with estrogen receptor (ERα)-positive breast cancer are treated with adjuvant endocrine therapy, including selective estrogen receptor modulators (SERMs) and/or aromatase inhibitors (AIs). However, more than 20% of patients relapse within 10 years and eventually progress to incurable metastatic disease. Here we demonstrate that the choice of therapy has a fundamental influence on the genetic landscape of relapsed diseases. We found that 21.5% of AI-treated, relapsed patients had acquired CYP19A1 (encoding aromatase) amplification (CYP19A1amp). Relapsed patients also developed numerous mutations targeting key breast cancer-associated genes, including ESR1 and CYP19A1. Notably, CYP19A1amp cells also emerged in vitro, but only in AI-resistant models. CYP19A1 amplification caused increased aromatase activity and estrogen-independent ERα binding to target genes, resulting in CYP19A1amp cells showing decreased sensitivity to AI treatment. These data suggest that AI treatment itself selects for acquired CYP19A1amp and promotes local autocrine estrogen signaling in AI-resistant metastatic patients.

Expression of p63 protein in anaplastic large cell lymphoma: implications for genetic subtyping

Anaplastic large cell lymphomas (ALCLs) are CD30-positive T-cell non-Hodgkin lymphomas that bear chromosomal rearrangements of the TP53 homologue TP63 in a subset of cases that demonstrate aggressive clinical behavior. In the present study, we examined the relationship between p63 protein expression by immunohistochemistry and the results of fluorescence in situ hybridization using TP63 probes in 116 ALCLs. We also determined the relative expression of full-length TAp63 and truncated ΔNp63 isoforms (eg, p40) in ALCL cell lines and a subset of clinical cases. Overall, 35.3% of ALCLs were positive for p63 protein. Primary cutaneous and anaplastic lymphoma kinase-negative ALCLs were positive more frequently than anaplastic lymphoma kinase-positive ALCLs (P=.0034). As previously reported, cases with TP63 gene rearrangements expressed p63 uniformly. p63 expression in nonrearranged cases was associated with extra copies of TP63 on 3q28 (P<.0001). Extra copies of TP63 correlated with extra copies of the DUSP22 locus on 6p25.3 (P<.0001). Results of immunohistochemistry, Western blotting, and RNA sequencing indicated that p63 expression in nonrearranged cases was entirely attributable to TAp63 isoforms. Taken together, these findings indicate that ALCLs without TP63 rearrangements may express TAp63 isoforms of p63 and that this expression is associated with extra copies of TP63, probably due to widespread genomic copy number abnormalities rather than focal gains. Immunohistochemistry for p63 in ALCL is not specific for TP63 rearrangements but is useful clinically as a screening test to select cases for further testing by fluorescence in situ hybridization. Immunohistochemistry for ΔNp63 (p40) is not informative in the evaluation of ALCL.

Immunocytochemical p63 expression discriminates between primary cutaneous follicle centre cell and diffuse large B cell lymphoma-leg type, and is of the TAp63 isoform

AIMS

The p63 gene shares structural and functional homologies with the p53 family of transcriptional activators, but differs in exhibiting a consistent expression pattern in normal tissues. Although p63 is rarely mutated in malignancy studies of primary human tumours and cell lines suggest that p63 may promote tumour development. In non-Hodgkin's nodal lymphoma, TAp63 expression in follicular lymphoma (54%) and diffuse large B cell lymphoma (34%) has been described and correlated with the proliferative index. In this study, we analysed a series of primary cutaneous B cell lymphomas for immunohistochemical expression of p63.

METHODS AND RESULTS

Thirty cases of diffuse large B cell lymphoma leg type (pcDLBCLL) and 34 cases of follicle centre cell lymphoma (pcFCCL) were stained using a generic antibody to p63, and a subset of these with an antibody specific for delta-Np63 isoform. The results indicate a significant difference between pcDLBCLL (21 of 30) and pcFCCL (four of 34) in p63 expression (P = 0.000); expression correlated strongly with the proliferation rate as assessed by Ki-67 (P = 0.015). None of the p63((+)) cases tested expressed the delta-Np63 isoform, suggesting that expression is of the TAp63 isoform.

CONCLUSIONS

Functional studies are required to clarify the significance of p63 overexpression in primary cutaneous B cell lymphoma.

p53 Family and Cellular Stress Responses in Cancer

p53 is an important tumor suppressor gene, which is stimulated by cellular stress like ionizing radiation, hypoxia, carcinogens, and oxidative stress. Upon activation, p53 leads to cell-cycle arrest and promotes DNA repair or induces apoptosis via several pathways. p63 and p73 are structural homologs of p53 that can act similarly to the protein and also hold functions distinct from p53. Today more than 40 different isoforms of the p53 family members are known. They result from transcription via different promoters and alternative splicing. Some isoforms have carcinogenic properties and mediate resistance to chemotherapy. Therefore, expression patterns of the p53 family genes can offer prognostic information in several malignant tumors. Furthermore, the p53 family constitutes a potential target for cancer therapy. Small molecules (e.g., Nutlins, RITA, PRIMA-1, and MIRA-1 among others) have been objects of intense research interest in recent years. They restore pro-apoptotic wild-type p53 function and were shown to break chemotherapeutic resistance. Due to p53 family interactions small molecules also influence p63 and p73 activity. Thus, the members of the p53 family are key players in the cellular stress response in cancer and are expected to grow in importance as therapeutic targets.

Characterization of specific p63 and p63-N-terminal isoform antibodies and their application for immunohistochemistry

The TP63 gene gives rise to protein isoforms with different properties and functions due to the presence (TAp63) or absence (ΔNp63) of an N-terminal p53-like transactivation domain. Immunohistochemistry for p63 has clinical value for certain tumour types, but investigations have been hampered by a lack of well characterized antibodies and the inability to discriminate between these N-terminal isoforms with opposite functional properties. We have extensively characterized a series of monoclonal antibodies to recombinant human TAp63 and two commercial p63 monoclonals by Western blot, immunostaining and phage display epitope mapping. Twenty-eight of 29 (96.6 %) novel monoclonals that recognized all p63 isoforms showed substantial cross-reactivity with p73, as did the commercial antibody, 4A4. One novel clone, PANp63-6.1, showed slight cross-reaction with p73 by Western blotting but not immunohistochemistry and the SFI-6 monoclonal did not cross-react with p73 or p53. Phage display revealed that the PANp63-6.1 epitope has one amino acid difference between p63 and p73, the 4A4 epitope is identical in both, whereas the SFI-6 epitope is unique to p63, accounting for these findings. We also produced and characterized a TAp63-specific clone that does not recognize p53 or p73, and we prepared polyclonal sera specific for ΔNp63 isoforms. Immunohistochemistry demonstrated that TAp63 is expressed in a variety of epithelial and other cell types during development, often in a converse pattern to ΔNp63, but has a very limited expression in normal adult tissues and is independent of ΔNp63. TAp63 was expressed in 17.6 % of squamous cancers of cervix that expressed p63, unlike normal cervix where TAp63 was not expressed. TAp63 did not associate with proliferative index, but cervical carcinomas with TAp63 expression showed improved survival. These data highlight the need for rigorous antibody characterization and indicate that p63-isoform identification may improve the clinical value of p63 expression analyses.

p63 and p53 expression in extranodal NK/T cell lymphoma, nasal type

OBJECTIVES

To investigate the pathological and clinical meaning of p63 in extranodal nasal type NK/T cell lymphoma (NKTCL).

METHODS

We detected p63 and p53 expression using immunohistochemistry staining in 84 cases of NKTCL from Southern of China, an area with a well known high incidence of nasopharyngeal carcinoma, which is closely associated with Epstein-Barr virus infection. Moreover, we analysed the relationship between p63 and p53 expression and the clinicopathological features of NKTCL.

RESULTS

Our results first showed that p63 expression was found in 14.3% (12/84) of NKTCL compared with 6.6% (2/30) in reactive lymphoid hyperplasia of nasopharynx. p63 Expression rate in NKTCL was significantly higher than that in reactive lymphoid hyperplasia of nasopharynx (p=0.016). NKTCL patients with p63 positivity had poorer 5-year overall survival rate (29.2%) than that (49.9%) of p63 negativity. p53 expression was found in 33.3% (28/84) of NKTCL. Our data showed that p53 expression was significantly associated with tumour stage (p=0.016) and international prognostic index (p=0.026) in patients with NKTCL. Cox regression test showed that p53 expression rate and international prognostic index score were statistically independent prognostic factors for NKTCL patients (p=0.002 and p=0.016, respectively). Our results suggest that p63 and p53 might play a role in pathogenesis of NKTCL.

Fludarabine nucleoside induces accumulations of p53, p63 and p73 in the nuclei of human B-lymphoid cell lines, with cytosolic and mitochondrial increases in p53

PURPOSE

Human Raji cells treated with fludarabine nucleoside (2-FaraA, 3 μM) undergo apoptosis with accumulation of p53 in the nuclei as multiple phosphorylated isoforms and C-terminal truncated derivatives. Changes induced by 2-FaraA in the levels of p53, p63 and p73 in the nuclear, cytosolic and mitochondrial fractions have been determined in four human B-lymphoid cell lines that are TP53-functional (Raji and IM9) and TP53-mutated (MEC1 and U266).

EXPERIMENTAL DESIGN

The B-lymphoid cell lines were treated with 2-FaraA (3 μM, 24 h, 48 h) and viability determined. Protein extracts of subcellular fractions from 2-FaraA-treated cells were analysed by 1D and 2D electrophoresis; multiple phosphorylated isoforms and truncated derivatives were identified by Western blots for p53, p63 and p73.

RESULTS

p53 and p63 were present in all three fractions, while p73 was only detected in nuclei. After treatment with 2-FaraA, nuclear p53, p63 and p73 accumulated as multiple phosphorylated isoforms and truncated derivatives. The association of p63 with mitochondria in human cells is novel.

CONCLUSIONS AND CLINICAL RELEVANCE

Comprehensive information on the subcellular distributions and responses of p53, p63 and p73 to 2-FaraA provides additional insight into mechanisms for induction of apoptosis in the treatment of B-lymphoproliferative disorders with fludarabine.

Role of p63 in Development, Tumorigenesis and Cancer Progression

The p53-related protein p63 has pleiotropic functions, including cell proliferation, survival, apoptosis, differentiation, senescence, and aging. The p63 gene is expressed as multiple isoforms that either contain an N-terminal p53-homologous transactivation domain (TAp63) or that lack this domain (ΔNp63). Multiple studies have demonstrated that p63 plays a crucial role in stratified epithelial development, and have shown the importance of p63 for maintaining proliferation potential, inducing differentiation, and preventing senescence. Additionally, much research focuses on the role of p63 in cancer progression. Clinical evidence suggests that p63 may play a role in inhibiting metastasis. Similarly, genetic mice models together with cell culture data strongly indicate that p63 deficiency may be a causative factor for metastatic spread. Moreover, the role of p63 in cancer metastasis has been shown to be greatly related to the ability of mutant p53 to promote cancer malignancy. However, there is still much confusion as to what the role of each specific isoform is. In this review, we highlight some of the major findings in the current literature regarding the role of specific p63 isoforms in development, tumorigenesis, and particularly in cancer metastasis.

Role of p53 family members p73 and p63 in human hematological malignancies

p53, mutated in over half of human cancers and about 13% of all hematological malignancies, maintains genomic integrity and triggers cellular senescence and apoptosis of damaged cells. In contrast to p53, the homologs p73 and p63 play critical roles in development of the central nervous system and skin/limbs, respectively. Moreover, dependent on the context they can exert tumor suppressor activities that cooperate with p53. Unlike p53, p73 and p63 are rarely mutated in cancers. Instead, up-regulation of the anti-apoptotic dominant-negative ΔNp73 and ΔNp63 isoforms is the most frequent abnormality in solid cancers. In hematological malignancies the most frequent p73 defect is promoter methylation and loss of expression, associated with unfavorable clinical outcomes. This suggests an essential tumor suppressor role of p73 in blood cells, also supported by genetic mouse models. Many therapeutic approaches aiming to restore p73 activity are currently being investigated. In contrast, the most frequent p63 abnormality is protein overexpression, associated with higher disease grade and poorer prognosis. Surprisingly, although available data are still scarce, the emerging picture is up-regulation of transactivation-competent TAp63 isoforms, suggesting a tumor-promoting role in this context.

Overexpression and ratio disruption of ΔNp63 and TAp63 isoform equilibrium in endometrial adenocarcinoma: correlation with obesity, menopause, and grade I/II tumors

PURPOSE

p63 plays an important role in several intracellular processes such as transcription activation and apoptosis. p63 has two N-terminal isoforms, TAp63 and ΔNp63. TAp63 isoform has p53-like functions, while ΔNp63 acts as a dominant negative inhibitor of the p53 family and is considered oncogenic. Although p63 and its isoforms are overexpressed in a wide variety of human malignancies such as cervical, head and neck, and lung cancer, their role in endometrial carcinoma has not been investigated.

METHODS

We measured by quantitative real-time polymerase chain reaction the mRNA expression of TAp63 and ΔNp63 in a series of 20 endometrioid adenocarcinomas paired with adjacent normal tissue.

RESULTS

TAp63 isoform exhibited 1.8-fold overexpression in malignant samples, while ΔNp63 was 4.3-fold overexpressed in cancer specimens. Further analysis revealed that the ΔN/TA isoform ratio shifted from 0.5 in normal samples to 1.2 in tumor specimens. Statistical analysis also revealed an association of TAp63 expression with high body mass index (p = 0.034), late menopause (p = 0.020), and lower tumor grade (p = 0.034). ΔNp63 was also correlated with grade I/II tumors (p = 0.044).

CONCLUSIONS

These results indicate that both p63 isoforms and especially ΔNp63 play an important role in the development and progression of grade I/II endometrial adenocarcinoma, especially in obese and late-menopause women.

p40 (ΔNp63) is superior to p63 for the diagnosis of pulmonary squamous cell carcinoma

Immunohistochemistry has recently emerged as a powerful ancillary tool for differentiating lung adenocarcinoma and squamous cell carcinoma-a distinction with important therapeutic implications. Although the most frequently recommended squamous marker p63 is extremely sensitive, it suffers from low specificity due to its reactivity in a substantial proportion of lung adenocarcinomas and other tumor types, particularly lymphomas. p40 is a relatively unknown antibody that recognizes ΔNp63-a p63 isoform suggested to be highly specific for squamous/basal cells. Here we compared the standard p63 antibody (4A4) and p40 in a series of 470 tumors from the archives of Memorial Sloan-Kettering Cancer Center and The Johns Hopkins Hospital, which included lung squamous cell carcinomas (n=81), adenocarcinomas (n=237), and large cell lymphomas (n=152). The p63 was positive in 100% of squamous cell carcinomas, 31% of adenocarcinomas, and 54% of large cell lymphomas (sensitivity 100%, specificity 60%). In contrast, although p40 was also positive in 100% of squamous cell carcinomas, only 3% of adenocarcinomas, and none of large cell lymphomas had p40 labeling (sensitivity 100%, specificity 98%). The mean percentage of p63 versus p40-immunoreactive cells in squamous cell carcinomas was equivalent (97 vs 96%, respectively, P=0.73). Rare adenocarcinomas with p40 labeling had reactivity in no more than 5% of tumor cells, whereas the mean (range) of p63-positive cells in adenocarcinomas and lymphomas was 26% (1-90%) and 48% (2-100%), respectively. In summary, p40 is equivalent to p63 in sensitivity for squamous cell carcinoma, but it is markedly superior to p63 in specificity, which eliminates a potential pitfall of misinterpreting a p63-positive adenocarcinoma or unsuspected lymphoma as squamous cell carcinoma. These findings strongly support the routine use of p40 in place of p63 for the diagnosis of pulmonary squamous cell carcinoma.

p63 is a suppressor of tumorigenesis and metastasis interacting with mutant p53

p53 mutations, occurring in two-thirds of all human cancers, confer a gain of function phenotype, including the ability to form metastasis, the determining feature in the prognosis of most human cancer. This effect seems mediated at least partially by its ability to physically interact with p63, thus affecting a cell invasion pathway, and accordingly, p63 is deregulated in human cancers. In addition, p63, as an 'epithelial organizer', directly impinges on epidermal mesenchimal transition, stemness, senescence, cell death and cell cycle arrest, all determinant in cancer, and thus p63 affects chemosensitivity and chemoresistance. This demonstrates an important role for p63 in cancer development and its progression, and the aim of this review is to set this new evidence that links p63 to metastasis within the context of the long conserved other functions of p63.

Role of p63 in cancer development

Since their initial identification p53 homologues p63 and p73 have been expected to play a role in cancer development due to their close homology to p53, notoriously one of the most mutated genes in cancer. However soon after their discovery the awareness that these genes were rarely mutated in cancer seemed to indicate that they did not play a role in its development. However a large number of data collected in the following years indicated that altered expression rather than mutation could be found in different neoplasia and play a role in its biology. In particular p63 due to its fundamental role in epithelial development seems to play a role in a number of tumors of epithelial origin. In this review we summarize some of the evidence linking p63 to carcinogenesis.

Apoptosis induced by genipin in human leukemia K562 cells: involvement of c-Jun N-terminal kinase in G₂/M arrest

AIM

To investigate the effect of genipin on apoptosis in human leukemia K562 cells in vitro and elucidate the underlying mechanisms.

METHODS

The effect of genipin on K562 cell viability was measured using trypan blue dye exclusion and cell counting. Morphological changes were detected using phase-contrast microscopy. Apoptosis was analyzed using DNA ladder, propidium iodide (PI)-labeled flow cytometry (FCM) and Hoechst 33258 staining. The influence of genipin on cell cycle distribution was determined using PI staining. Caspase 3 activity was analyzed to detect apoptosis at different time points. Protein levels of phospho-c-Jun, phosphor-c-Jun N-terminal kinase (p-JNK), phosphor-p38, Fas-L, p63, and Bax and the release of cytochrome c were detected using Western blot analysis.

RESULTS

Genipin reduced the viability of K562 cells with an IC(50) value of approximately 250 μmol/L. Genipin 200-400 μmol/L induced formation of typical apoptotic bodies and DNA fragmentation. Additionally, genipin 400 μmol/L significantly increased the caspase 3 activity from 8-24 h and arrested the cells in the G₂/M phase. After stimulation with genipin 500 μmol/L, the levels of p-JNK, p-c-Jun, Fas-L, Bax, and cytochrome c were remarkably upregulated, but there were no obvious changes of p-p38. Genipin 200-500 μmol/L significantly upregulated the Fas-L expression and downregulated p63 expression. Dicoumarol 100 μmol/L, a JNK1/2 inhibitor, markedly suppressed the formation of apoptotic bodies and JNK activation induced by genipin 400 μmol/L.

CONCLUSION

These results suggest that genipin inhibits the proliferation of K562 cells and induces apoptosis through the activation of JNK and induction of the Fas ligand.

The guardians of the genome (p53, TA-p73, and TA-p63) are regulators of tumor suppressor miRNAs network

The tumor suppressor p53 homologues, TA-p73, and p63 have been shown to function as tumor suppressors. However, how they function as tumor suppressors remains elusive. Here, I propose a number of tumor suppressor pathways that illustrate how the TA-p73 and p63 could function as negative regulators of invasion, metastasis, and cancer stem cells (CSCs) proliferation. Furthermore, I provide molecular insights into how TA-p73 and p63 could function as tumor suppressors. Remarkably, the guardians--p53, p73, and p63--of the genome are in control of most of the known tumor suppressor miRNAs, tumor suppressor genes, and metastasis suppressors by suppressing c-myc through miR-145/let-7/miR-34/TRIM32/PTEN/FBXW7. In particular, p53 and TA-p73/p63 appear to upregulate the expression of (1) tumor suppressor miRNAs, such as let-7, miR-34, miR-15/16a, miR-145, miR-29, miR-26, miR-30, and miR-146a; (2) tumor suppressor genes, such as PTEN, RBs, CDKN1a/b/c, and CDKN2a/b/c/d; (3) metastasis suppressors, such as Raf kinase inhibitory protein, CycG2, and DEC2, and thereby they enlarge their tumor suppressor network to inhibit tumorigenesis, invasion, angiogenesis, migration, metastasis, and CSCs proliferation.

TAp63 suppresses metastasis through coordinate regulation of Dicer and miRNAs

Aberrant expression of microRNAs (miRNAs) and the enzymes that control their processing have been reported in multiple biological processes including primary and metastatic tumours, but the mechanisms governing this are not clearly understood. Here we show that TAp63, a p53 family member, suppresses tumorigenesis and metastasis, and coordinately regulates Dicer and miR-130b to suppress metastasis. Metastatic mouse and human tumours deficient in TAp63 express Dicer at very low levels, and we found that modulation of expression of Dicer and miR-130b markedly affected the metastatic potential of cells lacking TAp63. TAp63 binds to and transactivates the Dicer promoter, demonstrating direct transcriptional regulation of Dicer by TAp63. These data provide a novel understanding of the roles of TAp63 in tumour and metastasis suppression through the coordinate transcriptional regulation of Dicer and miR-130b and may have implications for the many processes regulated by miRNAs.

NIR, an inhibitor of histone acetyltransferases, regulates transcription factor TAp63 and is controlled by the cell cycle

p63 is a sequence-specific transcription factor that regulates epithelial stem cell maintenance and epithelial differentiation. In addition, the TAp63 isoform with an N-terminal transactivation domain functions as an inducer of apoptosis during the development of sympathetic neurons. Previous work has indicated that the co-activator and histone acetyltransferase (HAT), p300, can bind to TAp63 and stimulate TAp63-dependent transcription of the p21Cip1 gene. Novel INHAT Repressor (NIR) is an inhibitor of HAT. Here, we report that the central portion of NIR binds to the transactivation domain and the C-terminal oligomerization domain of TAp63. NIR is highly expressed in G2/M phase of the cell cycle and only weakly expressed in G1/S. Furthermore, except during mitosis, NIR is predominantly localized in the nucleolus; only a small portion co-localizes with TAp63 in the nucleoplasm and at the p21 gene promoter. Consistent with NIR acting as a repressor, the induced translocation of NIR from the nucleolus into the nucleoplasm resulted in the inhibition of TAp63-dependent transactivation of p21. Conversely, knockdown of NIR by RNAi stimulated p21 transcription in the presence of TAp63. Thus, NIR is a cell-cycle-controlled, novel negative regulator of TAp63. The low levels of nucleoplasmic NIR might act as a buffer toward potentially toxic TAp63.

A rare association of B cell lymphoma and ectodermal dysplasia presenting with protein-losing enteropathy

This patient, known to have ectodermal dysplasia, was referred to the hospital to investigate the cause for his significant pedal oedema and hypoproteinaemia. Investigations ruled out protein loss from the kidney and there was no evidence of chronic liver disease. Protein-losing enteropathy became a diagnosis of exclusion. To investigate it further, he underwent an oral gastroduodenoscopy and a computed tomography scan of the abdomen, which showed an abnormal duodenal mucosa and extensive retroperitoneal lymphadenopathy. Biopsies confirmed this to be grade II follicular non-Hodgkin lymphoma. The lymphadenopathy was causing obstructive hydronephrosis, which required a nephrostomy. He received a course of steroids and chemotherapy. His condition, however, deteriorated and he died.

CD74 induces TAp63 expression leading to B-cell survival

Most mature follicular B cells circulate within the periphery in a quiescent state, without actively contributing to an acute immune response. Lasting B-cell persistence in the periphery is dependent on survival signals that are transduced by cell surface receptors. We recently demonstrated that cell surface CD74 controls mature B-cell survival. Stimulation of cell surface CD74 leads to NF-kappaB activation, which enables entry of the stimulated B cells into the S phase, induction of DNA synthesis, and cell division, and augments the expression of survival genes. In the present study, we investigated CD74 target genes to determine the identities of the molecules whose expression is modulated by CD74, thereby regulating B-cell survival. We report that CD74 activates the p65 member of the NF-kappaB family, which in turn up-regulates the expression of p53-related TAp63 proteins. TAp63 then binds and transactivates the Bcl-2gene and induces the production of Bcl-2 protein, thereby providing the cells with increased survival capacity. Thus, the CD74/NF-kappaB/TAp63 axis defines a novel antiapoptotic pathway in mature B cells, resulting in the shaping of both the B-cell repertoire and the immune response.

p53/p63/p73 isoforms: an orchestra of isoforms to harmonise cell differentiation and response to stress

p63, p73 and p53 compose a family of transcription factors involved in cell response to stress and development. p53 is the most frequently mutated gene in cancer (50%) and loss of p53 activity is considered to be ubiquitous to all cancers. Recent publications may have a profound impact on our understanding of p53 tumour suppressor activity. p63, p73 and p53 genes have a dual gene structure conserved in drosophila, zebrafish and man. They encode for multiple p63, p73 or p53 proteins containing different protein domains (isoforms) due to multiple splicing, alternative promoter and alternative initiation of translation. In this review, we describe the different isoforms of p63, p73, p53 and their roles in development and cancer. The changes in the interactions between p53, p63 and p73 isoforms are likely to be fundamental to our understanding in the transition between normal cell cycling and the onset of tumour formation.

Cleavage of the transactivation-inhibitory domain of p63 by caspases enhances apoptosis

p63 is a p53-related transcription factor. Utilization of two different promoters and alternative splicing at the C terminus lead to generation of six isoforms. The alpha isoforms of TAp63 and DeltaNp63 contain a transactivation-inhibitory (TI) domain at the C termini, which can bind to the transactivation (TA) domain and inhibit its transcriptional activity. Consequently, TAp63alpha can directly inhibit its activity through an intramolecular interaction; similarly, DeltaNp63alpha can inhibit the activity of the active TAp63 isoforms through an intermolecular interaction. In this work, we demonstrate that after induction of apoptosis, the TI domain of the p63alpha isoforms is cleaved by activated caspases. Cleavage of DeltaNp63alpha relieves its inhibitory effect on the transcriptionally active p63 proteins, and the cleavage of TAp63alpha results in production of a TAp63 protein with enhanced transcriptional activity. In agreement with these data, generation of the N-terminal TAp63 fragment has a role in apoptosis because stable cell lines expressing wild-type TAp63 are more sensitive to apoptosis compared with cells expressing the noncleavable mutant. We also used a model system in which TAp63 expression was induced by trichostatin-A treatment in HCT116 cells. Trichostatin-A sensitized these cells to apoptosis, and this sensitization was associated with cleavage of up-regulated p63.

Clinico-pathological characteristics of p63 expression in B-cell lymphoma

A member of the family of p53-related genes, p63 plays a role in regulating epithelial proliferation and differentiation programs, but the pathological and clinical meaning of p63 in B-cell lymphoma has not been elucidated. We investigated the expression pattern of p63 in B-cell malignancies, and evaluated the correlation between the expression of p63 and other germinal center markers. Ninety-eight B-cell lymphomas (28 FCL, 5 MCL, and 65 DLBCL) were analyzed by immunohistochemical examination for p63, bcl-6, CD10 and MUM-1 proteins, and for rearrangement of bcl-2/IgH. Expression of p63 was observed in the nuclei of tumor cells obtained from 15 of 28 (54%) FCL, 22 of 65 (34%) DLBCL, but none of 5 MCL. In DLBCL, the expression of p63 and bcl-6 showed a significant correlation (P < 0.02), but no correlation was observed between p63 and expression of CD10, MUM-1, or bcl-2/IgH rearrangement. RT-PCR revealed that TAp63alpha-type transcripts, a possible negative regulator of transcriptional activation of p21 promoter, were major transcripts in B-cell lymphoma tissues. As for prognostic significance, only patients in the p63 positive group of FCL died, and in the non-germinal center group, the p63 positive cases appeared to have inferior overall survival than other groups in DLBCL. Our preliminary results suggested that p63 expression is a disadvantageous factor for prognosis in this subgroup of B-cell lymphomas.

The role of p73 in hematological malignancies

The P73 gene is a homologue of the P53 tumor suppressor. Owing to its structural similarity with p53, p73 was originally considered to have tumor suppressor function. However, the discovery of N-terminal truncated isoforms with oncogenic properties showed a 'two in one' structure of its product, p73 protein. The full-length variants are strong inducers of apoptosis, whereas the truncated isoforms inhibit proapoptotic activity of p53 and the full-length p73. Thus, p73 is involved in the regulation of cell cycle, cell death and development. Moreover, it plays a role in carcinogenesis and controls tumor sensitivity to treatment. p73 is commonly expressed in tumor cells in hematological malignancies. Overexpression of p73 protein and aberrant expression of its particular isoforms, with very low frequency of P73 hypermethylation or mutations, were found in malignant myeloproliferations, including acute myeloblastic leukemia. In contrast, hypermethylation and subsequent inactivation of the P73 gene are the most common findings in malignant lymphoproliferative disorders, especially acute lymphoblastic leukemia (ALL) and non-Hodgkin's lymphomas. Assessment of P73 methylation may provide important prognostic information, as was confirmed in patients with ALL. This review summarizes some aspects of p73 biology with particular reference to its possible pathogenetic role and prognostic significance in hematological malignancies.

p63 heterozygous mutant mice are not prone to spontaneous or chemically induced tumors

Homology between p63 and p53 has suggested that these proteins might function similarly. However, the majority of data from human tumors have not supported a similar role for p63 in tumor suppression. To investigate this issue, we studied spontaneous tumorigenesis in p63+/- mice in both WT and p53-compromised backgrounds. We found that p63+/- mice were not tumor prone and mice heterozygous for both p63 and p53 had fewer tumors than p53+/- mice. The rare tumors that developed in mice with compromised p63 were also distinct from those of p53+/- mice. Furthermore, p63+/- mice were not prone to chemically induced tumorigenesis, and p63 expression was maintained in carcinomas. These findings demonstrate that, in agreement with data from human tumors, p63 plays a markedly different biological role in cancer than p53.