Expression of p63 (TA and ▴N isoforms) in human primary well differentiated buccal carcinomas

MiR-223-5p works as an oncomiR in vulvar carcinoma by TP63 suppression

MiR-223-5p has been previously mentioned to be associated with tumor metastasis in HPV negative vulvar carcinomas, such as in several other tumor types. In the present study, we hypothesized that this microRNA would be important in vulvar cancer carcinogenesis and progression. To investigate this, we artificially mimicked miR-223-5p expression in a cell line derived from lymph node metastasis of vulvar carcinoma (SW962) and performed in vitro assays. As results, lower cell proliferation (p < 0.01) and migration (p < 0.001) were observed when miR-223-5p was overexpressed. In contrast, increased invasive potential of these cells was verified (p < 0.004). In silico search indicated that miR-223-5p targets TP63, member of the TP53 family of proteins, largely described with importance in vulvar cancer. We experimentally demonstrated that this microRNA is capable to decrease levels of p63 at both mRNA and protein levels (p < 0.001, and p < 0.0001; respectively). Also, a significant inverse correlation was observed between miR-223-5p and p63 expressions in tumors from patients (p = 0.0365). Furthermore, low p63 protein expression was correlated with deeper tumor invasion (p = 0.0491) and lower patient overall survival (p = 0.0494). Our study points out miR-223-5p overexpression as a putative pathological mechanism of tumor invasion and a promising therapeutic target and highlights the importance of both miR-223-5p and p63 as prognostic factors in vulvar cancer. Also, it is plausible that the evaluation of p63 expression in vulvar cancer at the biopsy level may bring important contribution on prognostic establishment and in elaborating better surgical approaches for vulvar cancer patients.

The Regulation of Tumor Suppressor p63 by the Ubiquitin-Proteasome System

The protein p63 has been identified as a homolog of the tumor suppressor protein p53 and is capable of inducing apoptosis, cell cycle arrest, or senescence. p63 has at least six isoforms, which can be divided into two major groups: the TAp63 variants that contain the N-terminal transactivation domain and the ΔNp63 variants that lack the N-terminal transactivation domain. The TAp63 variants are generally considered to be tumor suppressors involved in activating apoptosis and suppressing metastasis. ΔNp63 variants cannot induce apoptosis but can act as dominant negative inhibitors to block the function of TAp53, TAp73, and TAp63. p63 is rarely mutated in human tumors and is predominately regulated at the post-translational level by phosphorylation and ubiquitination. This review focuses primarily on regulation of p63 by the ubiquitin E-3 ligase family of enzymes via ubiquitination and proteasome-mediated degradation, and introduces a new key regulator of the p63 protein.

Differential expression of microRNAs miR-21, miR-31, miR-203, miR-125a-5p and miR-125b and proteins PTEN and p63 in verrucous carcinoma of the head and neck

AIMS

To investigate the expression of microRNAs miR-21, miR-31, miR-203, miR-125a-5p and miR-125b and proteins phosphatase and tensin homologue (PTEN) and p63 in verrucous carcinoma (VC) of the head and neck.

METHODS AND RESULTS

Thirty cases of VC, 50 cases of conventional squamous cell carcinoma (SCC) and 30 samples of normal epithelium of the head and neck were included. Real-time polymerase chain reaction and immunohistochemistry were used to analyse the expression of microRNAs and proteins, respectively. In comparison to normal epithelium, miR-21 was overexpressed in both VC and SCC and miR-31 was overexpressed in VC and in well- and moderately differentiated SCC. Levels of miR-203 were elevated in VC but unaltered or reduced in SCC, and levels of miR-125a-5p and miR-125b were reduced in VC but unaltered in SCC. PTEN was down-regulated in both VC and SCC, whereas p63 was down-regulated in VC but up-regulated in SCC. Differential expression of p63 in VC correlated inversely with the expression of miR-21 and miR-203.

CONCLUSIONS

Differences between VC, SCC and normal epithelium in expression profiles of investigated molecules indicate their association with the pathogenesis and clinicopathological characteristics of VC. Our results suggest that some microRNAs and proteins, particularly miR-125b, miR-203 and p63, might be useful in the diagnosis of VC.

Dysregulated ΔNp63α inhibits expression of Ink4a/arf, blocks senescence, and promotes malignant conversion of keratinocytes

p63 is critical for squamous epithelial development, and elevated levels of the ΔNp63α isoform are seen in squamous cell cancers of various organ sites. However, significant controversy exists regarding the role of p63 isoforms as oncoproteins or tumor suppressors. Here, lentiviruses were developed to drive long-term overexpression of ΔNp63α in primary keratinocytes. Elevated levels of ΔNp63α in vitro promote long-term survival and block both replicative and oncogene-induced senescence in primary keratinocytes, as evidenced by the expression of SA-β-gal and the presence of nuclear foci of heterochromatin protein 1γ. The contribution of ΔNp63α to cancer development was assessed using an in vivo grafting model of experimental skin tumorigenesis that allows distinction between benign and malignant tumors. Grafted lenti-ΔNp63α keratinocytes do not form tumors, whereas lenti-GFP/v-ras^Ha keratinocytes develop well-differentiated papillomas. Lenti-ΔNp63α/v-ras^Ha keratinocytes form undifferentiated carcinomas. The average volume of lenti-ΔNp63α/v-ras^Ha tumors was significantly higher than those in the lenti-GFP/v-ras^Ha group, consistent with increased BrdU incorporation detected by immunohistochemistry. The block in oncogene-induced senescence corresponds to sustained levels of E2F1 and phosphorylated AKT, and is associated with loss of induction of p16^ink4a/p19^arf. The relevance of p16^ink4a/p19^arf loss was demonstrated in grafting studies of p19^arf-null keratinocytes, which develop malignant carcinomas in the presence of v-ras^Ha similar to those arising in wildtype keratinocytes that express lenti-ΔNp63α and v-ras^Ha. Our findings establish that ΔNp63α has oncogenic activity and its overexpression in human squamous cell carcinomas contributes to the malignant phenotype, and implicate its ability to regulate p16^ink4a/p19^arf in the process.

Expression and regulation of the ΔN and TAp63 isoforms in salivary gland tumorigenesis clinical and experimental findings

The TP63 gene, a TP53 homologue, encodes for two main isoforms by different promoters: one retains (TA) and the other lacks (ΔN) the transactivation domain. p63 plays a critical role in the maintenance of basal and myoepithelial cells in ectodermally derived tissues and is implicated in tumorigenesis of several neoplastic entities. However, the biological and regulatory roles of these isoforms in salivary gland tumorigenesis remain unknown. Our results show a reciprocal expression between TA and ΔN isoforms in both benign and malignant salivary tumors. The most dominantly expressed were the ΔN isoforms, whereas the TA isoforms showed generally low levels of expression, except in a few tumors. High ΔNp63 expression characterized tumors with aggressive behavior, whereas tumors with high TAp63 expression were significantly smaller and less aggressive. In salivary gland cells, high expression of ΔNp63 led to enhanced cell migration and invasion and suppression of cell senescence independent of TAp63 and/or TP53 gene status. We conclude the following: i) overexpression of ΔNp63 contributes to salivary tumorigenesis, ii) ΔNp63 plays a dominant negative effect on the TA isoform in the modulation of cell migration and invasion, and iii) the ΔN isoform plays an oncogenic role and may represent an attractive target for therapeutic intervention in patients with salivary carcinomas.

p53 and its mutants in tumor cell migration and invasion

In about half of all human cancers, the tumor suppressor p53 protein is either lost or mutated, frequently resulting in the expression of a transcriptionally inactive mutant p53 protein. Loss of p53 function is well known to influence cell cycle checkpoint controls and apoptosis. But it is now clear that p53 regulates other key stages of metastatic progression, such as cell migration and invasion. Moreover, recent data suggests that expression of mutant p53 is not the equivalent of p53 loss, and that mutant p53s can acquire new functions to drive cell migration, invasion, and metastasis, in part by interfering with p63 function.

Clinical relevance of the putative stem cell marker p63 in breast cancer

P63 is a member of the p53 family. This protein is crucial for the maintenance of a stem cell population in the human epithelium and necessary for the normal development of all epithelial tissues including mammary glands. In normal breast tissue, the p63 seems to be a specific myoepithelial cell marker. P63 expression has been described in highly aggressive ER negative basal-like breast tumors. The value of p63 expression in ER positive disease is less clear. The expression levels of p63 mRNA by Affymetrix microarray analysis in a combined cohort of 2,158 ER positive breast cancers and its prognostic and predictive impact were analyzed. Tumor samples containing large amounts of benign breast tissue, which will interfere with p63 measurement, were excluded prior to the analysis. Survival analysis revealed a better prognosis of ER positive breast cancer expressing p63 (n = 410; P < 0.036). No correlation of p63 with standard parameters was observed. In a subgroup analysis, endocrine-treated patients with high p63 expression showed a better prognosis than low p63 expression (P = 0.06; n = 186). In untreated patients, this effect was less clear (n = 148; P = 0.5). P63 is a positive prognostic factor in endocrine-treated ER positive breast cancer and might influence responsiveness to endocrine treatment. Thus, p63 could be helpful as a predictive factor for endocrine therapy.

P63 expression in conjunctival proliferative diseases: pterygium and laryngo-onycho-cutaneous (LOC) syndrome

PURPOSE

Compare expression of p63 in pterygium and laryngo-onycho-cutaneous (LOC) syndrome with normal conjunctiva.

METHODS

P63 immunohistochemical detection was carried out in normal, pterygium, and LOC conjunctival tissue. In vitro, growth of normal conjunctival biopsy specimens, pterygium, and LOC in growth tissue was compared.

RESULTS

In normal conjunctiva, p63 was poorly expressed in the infranasal quadrant, with 36% of cells stained vs. 55 to 59% in other quadrants (p < 0.05). In pterygium, p63 was overexpressed (59% cells stained) compared to normal supranasal (55%) and normal infranasal conjunctiva (36%, p < 0.05). In LOC, p63 was only expressed in 39% of cells vs. 58% in normal supratemporal conjunctiva (p < 0.05). Cytokeratin 19 was expressed by all cells cultured from normal conjunctival tissue.

CONCLUSIONS

This study emphasizes the importance of using control tissue explanted from the correspondent conjunctival quadrant when studying proliferative disorders. Different pathogenesis may account for the differences in p63 expression between pterygium and LOC.

p63: defining roles in morphogenesis, homeostasis, and neoplasia of the epidermis

p63 is a member of a gene family also including the p53 tumor suppressor and p73. In contrast to p53, p63 is rarely mutated in human cancers. Rather, gene amplification and dysregulated expression of p63 protein have been observed, particularly in squamous cell carcinomas. p63 is essential for development of stratified squamous epithelium, including the epidermis. The p63 gene is expressed as multiple protein isoforms with different functional capacities, and the balance of these isoforms, along with the presence or absence of the other family members, p53 and p73, can impact biological outcome. Both gene silencing and overexpression approaches have been utilized to elucidate the contributions of specific p63 isoforms to normal epidermal morphogenesis and tissue maintenance. While numerous studies have established the essential nature of p63 in the epidermis, the basis of this requirement, and the unique, as well as, overlapping functions of the individual isoforms, remain controversial. In this review, we summarize the current understanding of roles played by specific p63 isoforms within the context of epidermal morphogenesis and homeostasis of the established epidermis, and the potential impact of p63 dysregulation on cancer development.

Reverse transcription-polymerase chain reaction and western blotting analysis for detection of p63 isoforms in uterine cervical cancers

The aim of this study was to investigate the role of TAp63 and DeltaNp63 isoforms in uterine cervical cancers. The messenger RNA (mRNA) and protein expressions of TA and DeltaN forms as well as alpha, beta, and gamma isoforms of p63 were studied in seven SiHa, ME-180, SNU17, SNU902, SNU1160, SNU703, and SNU1299 human papillomavirus (HPV)-positive uterine cervical squamous cell carcinoma (SCC) cell lines, one HT3 HPV-negative SCC cell line, and one HeLa adenocarcinoma cell line using reverse transcription-polymerase chain reaction (RT-PCR) and western blotting. Fresh nonneoplastic and neoplastic tissues of uterine cervical and endometrial cancers were also studied. RT-PCR for TA and DeltaN form and three isoforms of p63 showed positive bands for both TA and DeltaN forms and for all three isoforms in cervical cancer cell lines but weak band for alpha isoform in HPV-negative HT3 SCC cell line and no band for beta isoform in HeLa adenocarcinoma cell line. RT-PCR for TA and DeltaN and three isoforms of p63 mRNA in tissue samples showed positive bands in almost all samples, except for gamma isoform, the expression was weak or absent in nonneoplastic tissues compared with neoplastic tissues. In western blotting, cancer cell lines and both nonneoplastic and neoplastic tissue samples showed expression of TA and DeltaN, and gamma isoform but beta isoform expression with or without alpha isoform was only found in cancer cell lines and neoplastic tissues. beta isoform, possibly of DeltaNp63, may be considered as an important isoform in uterine cervical squamous cell carcinogenesis.

DeltaNp63 protein expression in uterine cervical and endometrial cancers

PURPOSE

To investigate the significance of p63 expression in uterine cervical and endometrial cancers.

MATERIALS AND METHODS

DeltaNp63 protein expression was studied in a variety of 127 cases of uterine cervical lesions (20 non-neoplastic cervices, 43 cervical intraepithelial neoplasia [CIN], 54 squamous cell carcinomas (SCCs), 40 adenocarcinomas, and 13 other histologic types) and 30 endometrioid type of endometrial adenocarcinomas by using immunohistochemistry. One SCC cell line (ME-180) and one adenocarcinoma cell line (HeLa) were also included.

RESULTS

In uterine cervix, the expression of DeltaNp63 was increased with progression of CIN, and positive in all SCCs, transitional cell carcinomas, and adenoid basal carcinoma, but negative in all adenocarcinomas. Adenosquamous cell carcinoma and mixed neuroendocrine and squamous cell carcinoma were positive in squamous component, but not in adenocarcinoma and neuroendocrine carcinoma components. ME-180 cell line was positive, whereas HeLa cell line was negative. Endometrioid type of endometrial adenocarcinomas showed a positive staining in glandular (26.7%) and squamous component.

CONCLUSIONS

Immunohistochemical staining for DeltaNp63 is a powerful marker for squamous differentiation and useful in exclusion of glandular and neuroendocrine differentiation in uterine cervical cancers, but not always in endometrial cancers.

Unique domain functions of p63 isotypes that differentially regulate distinct aspects of epidermal homeostasis

p63 is critical for squamous development and exists as multiple isotypes of two subclasses, TA and DeltaN. DeltaNp63 isotypes can antagonize transcription by TAp63 and p53, and are highly expressed in squamous cell cancers. Using mouse keratinocytes as a biological model of squamous epithelium, we show that multiple p63 isotypes, DeltaN- and TA-containing, are expressed and differentially modulated during in vitro murine keratinocyte differentiation. DeltaNp63alpha declines with Ca2+-induced differentiation, while a smaller DeltaN-form, DeltaNp63s, persists, suggesting unique functions of the two DeltaN-forms. To investigate the impact of dysregulated p63 expression that is observed in cancers and to define the biological contribution of the different domains of the p63 isotypes, DeltaNp63alpha, DeltaNp63p40, TAp63alpha, TAp63gamma or beta-galactosidase were overexpressed in primary murine keratinocytes. Microarray, RT-PCR and western blot analyses revealed that overexpression of DeltaNp63p40, which lacks the entire alpha-tail present in DeltaNp63alpha, permits expression of a full panel of differentiation markers. This is in contrast to overexpression of the full-length DeltaNp63alpha, which blocks induction of keratin 10, loricrin and filaggrin. These findings support a role for the alpha-tail of DeltaNp63alpha in blocking differentiation-specific gene expression. Overexpression of either TAp63 isotype permits keratin 10 and loricrin expression, thus the alpha-terminus requires the cooperation of the DeltaN domain in blocking early differentiation. However, both TA isotypes block filaggrin induction. The DeltaN-terminus is sufficient to maintain keratinocytes in a proliferative state, as both DeltaN forms block Ca2+-mediated p21WAF1 induction and S-phase arrest, while sustaining elevated PCNA levels. No alteration in cell cycle regulation was observed in keratinocytes overexpressing TAp63alpha or TAp63gamma. Clarifying the functional distinctions between p63 isotypes and domains will help to elucidate how their dysregulation impacts tumor biology and may suggest novel therapeutic strategies for modulating behavior of tumor cells with altered expression of p53 family members.

Expression of p63 protein and mRNA in oral epithelial dysplasia

BACKGROUND

Abnormalities in the TP53 are regarded as the most consistent findings in oral squamous cell carcinoma. Two related members of the TP53 family, p73 and p63, have shown remarkable structural similarity to TP53, indicating possible functional and biological interactions. The aim of the present study was to investigate the expression of p63 protein and mRNA in oral epithelial dysplasia.

METHODS

Immunohistochemical p63 staining was compared for samples from 90 male patients with buccal epithelial dysplasias and 15 healthy individuals with normal buccal mucosa and 15 subjects with reactive epithelial hyperplasia of the oral mucosa secondary to traumatic insult. The buccal lesions consisted of mild, moderate and severe epithelial dysplasias (30 samples in each category). The mRNA expression using reverse transcription polymerase chain reaction (RT-PCR) was also included for a subset of available fresh tissue specimens (four samples in each category of mild and moderate epithelial dysplasia; five samples in severe epithelial dysplasia; five samples in each of normal and reactive epithelial hyperplasia).

RESULTS

Nuclear p63 staining was demonstrated predominantly in the basal layers of the epithelium of the normal buccal mucosa and reactive epithelial hyperplasia specimens. For epithelial dysplasia lesions, however, staining was not restricted to the basal layers, extending to the middle spinous layer for samples in the mild category, with p63 immunoexpression observed across almost the full thickness of the dysplastic epithelium for analogous moderate and severe specimens. Compared with normal/reactive hyperplastic mucosa, p63 staining in the dysplastic mucosa was significantly increased. The severity of dysplasia was increased with the increase of p63 staining. Furthermore, Delta Np63mRNA was identified in all of the fresh tissue samples whereas expression of transactivation (TA) isotype was not detected. A subset of moderate epithelial dysplasia and severe variant showing p63-positive staining has undergone malignant transformation to squamous cell carcinomas in about 5 years follow-up.

CONCLUSION

Our results indicate that impaired p63 immunoexpression (predominantly Delta N isoform) is associated with the severity of oral epithelial dysplasias and up-regulation of p63 may play a role in the early stage of human oral tumorigenesis.

Tumor predisposition in mice mutant for p63 and p73: evidence for broader tumor suppressor functions for the p53 family

p63 and p73 are functionally and structurally related to the tumor suppressor p53. However, their own role in tumor suppression is unclear. Given the p53-like properties of p63 and p73, we tested whether they are involved in tumor suppression by aging mice heterozygous for mutations in all p53 family genes and scored for spontaneous tumors. We show here that p63+/-;p73+/- mice develop spontaneous tumors. Loss of p63 and p73 can also cooperate with loss of p53 in tumor development. Mice heterozygous for mutations in both p53 and p63 or p53 and p73 displayed higher tumor burden and metastasis compared to p53+/- mice. These findings provide evidence for a broader role for the p53 family than has been previously reported.