S100A14 inhibits proliferation of oral carcinoma derived cells through G1-arrest

Summary

Altered expression of S100A14 has been reported in various human cancers including oral squamous cell carcinomas (OSCCs). Its biological functions in carcinogenesis, however, are largely unknown. This study aimed to investigate the functional role of S100A14 in tumor cell proliferation and its possible functional association with p53. S100A14 protein was found to be gradually down-regulated during the transition from normal to dysplastic and carcinoma cells in an in vitro human OSCC progression model. When over-expressed by employing retroviral expression vector, S100A14 inhibited proliferation of CaLH3 and OSCC1, OSCC cell-lines harboring wild type (wt) p53, by inducing G1-arrest. This G1-arrest correlated with up-regulation of p21 both in the CaLH3 and OSCC1 cell-lines. shRNA mediated silencing of p53 led to partial suppression of p21 in S100A14 over-expressing CaLH3 cells, indicating that p21 up-regulation was, at least, partly dependent on p53. We further demonstrated that nuclear accumulation of p53 occurred with over-expression of S100A14 in CaLH3 cells. Our data suggest a novel role of S100A14 in OSCC cell proliferation by inducing G1-arrest and also indicate a functional link between S100A14 and the tumor suppressor protein p53.

Introduction

The S100 protein family represents the largest subgroup of calcium binding EF-hand type proteins. These proteins have been reported to be involved in a range of biological functions such as cell proliferation, cell motility, signal transduction, transcription, apoptosis and cell survival that are related both to normal development and tumorigenesis.[1], [2] Several S100 proteins, namely S100A2³, S100A4⁴, S100A6⁵ and S100B[6], [7] have been shown to interact with the tumor suppressor protein p53 with different functional consequences. In addition, p53-dependent transcriptional regulation has been suggested for members of the S100 genes such as S100A2,⁸ S100A6⁹ and S100A9.¹⁰ p53 is a transcriptional activator of many genes involved in important cellular functions such as cell cycle arrest, apoptosis and DNA repair.¹¹ p21^WAF1/CIP1 (p21) is a key transcriptional target of p53 and its transcriptional activation and subsequent G1-phase cell cycle arrest is critical for tumor suppressive functions.¹²

S100A14 is a recently identified member of the S100 protein family.[13], [14] Differential expression of S100A14 has been reported in a number of different human malignancies like ovary, breast, uterus, kidney, rectum and colon cancers, and esophageal and oral squamous cell carcinomas (OSCCs).[13], [15], [16], [17] Recently, we have demonstrated that S100A14 is involved in the regulation of OSCC cell invasion by modulating expression and activity of MMP1 and MMP9.¹⁸ In addition, Chen et al. have shown that p53 is a transcriptional regulator of S100A14 gene.¹⁹ Based on their findings, the authors have suggested that S100A14 might function as a tumor suppressor in a p53 mediated pathway.¹⁹ However, whether S100A14 has any functional effects on p53 and p53 mediated tumor suppressor functions are currently unknown. Given the differential expression of S100A14 in many tumors types and its possible involvement in p53 mediated tumor suppressor pathway, we hypothesized that similar to other members of the S100 proteins, S100A14 might be involved in biological functions relevant for human carcinogenesis. In this study, we investigated the role of S100A14 in tumor cell proliferation and its possible functional association with p53.

Here we demonstrate that over-expression of S100A14 inhibits proliferation of CaLH3 and OSCC1 cells due to G1-phase cell cycle arrest and is associated with up-regulation of cyclin dependent kinase inhibitor (CDKi) p21.