Dysregulation of TAp63 mRNA and protein levels in psoriasis.

Psoriasis is a chronic and excessive inflammation of the skin and is currently incurable. The cause of psoriasis remains poorly understood and a central and cooperative role for keratinocytes and T-cells in triggering the disease is highlighted. The p63 gene encodes six different proteins with homology to the tumor suppressor protein p53 that are crucial for normal development of ectodermally derived structures such as skin and oral mucosa. In this study, we have analyzed levels of the different p63 isoforms using quantitative reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry in 15 patients diagnosed with psoriasis. Quantitative RT-PCR results showed downregulation of the full-length TAp63 in psoriatic lesions compared to both clinically normal skin from patients (P<0.001) and matched healthy controls (P<0.001); however, p63 protein levels detected by immunohistochemistry were similar. All psoriasis lesions also had detectable levels of activated Stat3, a protein indicated in development of the disease, whereas control tissue lacked this protein. The present data show a different regulation of TAp63 in psoriasis, where the discrepancy between mRNA levels and protein expression indicates a post-transcriptional regulation analogous to that seen in p53.

Endogenous p63 acts as a survival factor for tumour cells of SCCHN origin.

The human p63 gene encodes a series of proteins that differ in their N- and/or C-terminal sequences and have widely differing properties in promoting or repressing p53-related functions such as growth arrest and apoptosis. In addition, p63 has important roles in the maintenance and differentiation of epithelial cell populations. Squamous cell carcinomas of the head and neck (SCCHN) express high levels of DeltaNp63 and p63beta isoforms compared to normal tissue from the same patients, suggesting a role for these isoforms in the pathogenesis of this common human malignancy. Here, we explore the function of p63 in SCCHN cells by using small interfering RNA (siRNA) to silence the expression of different isoforms in two SCCHN cell lines, FaDu and SCC-25. Silencing results in statistically significant decreased survival for tumour cells when all p63 isoforms, the N-terminal truncated or the alpha isoforms are inhibited. No effect was observed on cell proliferation or on the expression of epithelial differentiation markers. We also demonstrate that inhibition of endogenous p63 expression sensitises cells to the effects of ionizing radiation and cisplatin, common treatments for SCCHN patients. The data indicate that p63 has oncogenic properties in SCCHN and is predominantly involved in maintaining cell survival, rather than acting as a directly proliferative factor or as an inhibitor of terminal differentiation. Moreover, targeted inhibition of p63 expression in SCCHN could be a useful adjunct for conventional treatments of this disease.

Function and importance of p63 in normal oral mucosa and squamous cell carcinoma of the head and neck.

BACKGROUND/AIMS: Squamous cell carcinoma of the head and neck (HNSCC) is the 6th most common malignancy worldwide with a 5-year survival that has not improved over the last 20-25 years. Factors of prognostic significance for this tumour type include the presence of regional lymph node metastasis and amplification of chromosome 3q21-29, where the p63 gene is located. This gene encodes 6 proteins and is crucial for formation of the oral mucosa, teeth, salivary glands and skin. Each of the 6 different p63 proteins has different characteristics and functions, where some resemble the tumour suppressor protein p53, whilst others have functions that oppose p53. METHODS: To understand the function and importance of p63 in oral mucosa and tumour development we have studied protein as well as mRNA expression in normal oral mucosa and tumours. RESULTS/CONCLUSION: Expression of p63 proteins differs between the cell layers in normal oral mucosa, and primary HNSCC has a high expression level of p63 isoforms normally expressed in basal cells. Data suggest that p63 expression in HNSCC influences tumour cell differentiation.

Complex p63 mRNA isoform expression patterns in squamous cell carcinoma of the head and neck.

The human p63 gene encodes a series of protein isoforms that differ in their N- and/or C-terminal sequences and possess widely varying activities in promoting or repressing p53-related functions and in regulating the proliferation and differentiation of epithelial cells. To gain further information on the role of p63 expression in human tumours, we used quantitative real-time RT-PCR to study individual p63 isoforms in squamous cell carcinomas of the head and neck (SCCHN). In keeping with previous reports, expression of the deltaN- and p63alpha-isoforms predominated and deltaNp63 mRNA was expressed at significantly higher levels in tumours compared to matched normal tissues. Some tumours also expressed the highly efficient transactivator TA- and p63beta-isoforms, and p63beta was significantly increased in tumours compared to matched normal tissue. We could not identify any correlations between different p63-isoform expression patterns and proliferation, p53 status, or telomerase expression. All p63 isoforms could be identified in normal surface epithelium, and micro-dissection showed that the high levels present in basal layers were similar to those seen in tumour tissues. Thus, high-level expression of deltaNp63 in tumour cells may represent maintained expression by the basal cells from which the tumour arose, rather than representing a true over-expression of p63 during tumourigenesis. Tobacco usage, a genotoxic predisposing factor for SCCHN, had no effect on p63 expression in oral epithelium. Taken together, our data indicate that SCCHN maintain expression of high levels of deltaNp63alpha in combination with varying levels of other p63 isoforms, some of which are highly efficient transcriptional activators. The complexity of these p63 expression patterns seen in primary SCCHN indicates that p63 has multifaceted roles in tumour biology.