Induction of stanniocalcin-1 expression in apoptotic human nasopharyngeal cancer cells by p53

There is growing evidence to suggest that altered patterns of STC1 gene expression relate to the process of human cancer development. Our previous study has demonstrated the involvement of HIF-1 in the regulation of STC1 expression in human cancer cells. Recently, STC1 has been implicated as a putative pro-apoptotic factor in regulating the cell-death mechanism. Thus it would be of interest to know if STC1 is regulated by a tumor suppressor protein, p53. In this study, we provide evidence to demonstrate that the induction of STC1 expression in apoptotic human nasopharyngeal cancer cells (CNE2) is mediated by the activation of p53. Our study indicated that the activation of STC1 and heat-shock protein (hsp70) accompanied iodoacetamide (IDAM)-induced apoptosis in CNE-2. In addition, cellular events such as GSH depletion, mitochondrial membrane depolarization, reduction of pAkt and procaspase-3, and the induction of total p53 protein, acetylated p53, and annexin V positive cells were observed. The activation of STC1 was found to be at the transcriptional level and was independent of prior protein synthesis. Co-treatment of IDAM exposed cells with N-acetyl cysteine (NAC) prevented cell death by restoring mitochondrial membrane potential and cellular levels of GSH. NAC co-treatment also suppressed STC1 expression but had no effect on IDAM-induced hsp70 expression. RNA interference studies demonstrated that endogenous p53 was involved in activating STC1 gene expression. Collectively, the present findings provide the first evidence of p53 regulation of STC1 expression in human cancer cells.