Up-regulation of the tumor suppressor gene p53 and WAF1 gene expression by IP6 in HT-29 human colon carcinoma cell line

Abstract

Inositol hexaphosphate (InsP6 or IP6) ubiquitous in various cells has a novel anti-cancer action both in vivo and in vitro. IP6 inhibits cell growth, decreases cell proliferation and also causes differentiation of various cell lines, including HT-29 human colon carcinoma cell. We hypothesize that the tumor suppressor genes such as p53 and WAF1/CIP1 may be involved in mediating the anti-neoplastic action of IP6 p53 acts as a molecular policeman prevention of genetically damaged cells; it causes the cells to arrest in the G1 phase of cell cycle, and regulates the level of p21waf1/cip1 which acts as a growth inhibitor. We therefore investigated the effects of IP6 on the expression of p53 and WAF1/p21 in HT-29 human colon carcinoma by immunocytochemistry and quantitative ELISA. Our immunocytochemical studies with anti p53 antibodies (wild type-PAb246 and PAb1620) and anti p21waf1/cip1 (EA10) antibodies demonstrated an increased level of p53 and p21waf1/cip1 after 3 and 6 days of treatment with 3.3 and 5 mM IP6. Quantitative assay for p53 and p21waf1/cip1 by ELISA did not show detectable levels in untreated control cells, while strong expression of p53 and p21waf1/cip1 protein by 3.3 and 5 mM IP6 was seen on day 3 and day 6 of treatment. This increase was dose-dependent; however, a definite time-dependent increase was not observed. These data demonstrate that IP6 up-regulates the expression of the tumor suppressor gene p53 and p21WAF1/CIP1 gene and their modulation may be one of the mechanisms of the anti-neoplastic action of IP6. Since loss of p53 function enhances cancer cells' resistance to chemotherapeutic agents, the stimulating function of IP6 on p53 makes it an attractive adjuvant chemotherapeutic agent as well.