Overexpression of ΔNp63 in a Human Nasopharyngeal Carcinoma Cell Line Downregulates CKIs and Enhances Cell Proliferation

p63 belongs to a member of the tumor suppressor protein p53 family. Due to alternative promoter usage, two types of p63 proteins are produced. The Delta Np63 isoform lacks the N-terminal transactivation domain and is thought to antagonize TAp63 and p53 in target gene regulation. Delta Np63 has been found to be overexpressed in numerous human squamous cell carcinomas, including nasopharyngeal carcinoma (NPC). However, the role of Delta Np63 overexpression in NPC pathogenesis has not been clear. In this study, we use a Delta Np63 overexpressing human NPC cell line (NPC-076) to explore the possible roles of Delta Np63 in cell proliferation and cell-cycle regulation. We found that the proliferation of NPC-076 cell is greatly suppressed when the overexpressed Delta Np63 is silenced by specific Delta Np63 siRNA. Further studies show that Delta Np63 silencing results in the upregulation of CKIs, including p27(kip1) and p57(kip2) in both mRNA and protein levels. Cell-cycle analysis shows that Delta Np63 silencing also results in an increased G I phase cell and apoptotic cell population. Our findings indicate that Delta Np63 plays important roles in the regulation of NPC-076 cell-cycle progression, and may play a role in the maintenance of NPC-076 tumor cell phenotype.