UDP‐glucuronosyltransferase 1 (UGT1) knockdown in colon epithelial cells causes inactivation of P53 mediated apoptosis and increases colon tumorigenesis (LB599)

Abstract

Significant evidence demonstrates a pattern of down‐regulation of UGT expression in tumor tissue when compared to surrounding healthy tissue. This indicates the loss of UGT expression may be an early marker in the process of tissue neoplastic transformation. Although the UGTs are usually considered to be a metabolic defense against chemical carcinogens through glucuronidation, the underlying mechanism is still unclear. Here we show that UGT1 silenced by UGT1A siRNA in HT29 and LS180 colon epithelial cells decreases actinomycin D and etoposide‐induced P53 protein expression. Also observed is a reduction in P21, BAX, and caspase‐3, with a lowering of the cytotoxicity of these two chemicals, indicating inactivation of P53 mediated apoptosis. To identify this phenomenon in vivo, intestinal epithelial cell (IEC)‐specific Ugt1 knockout (Ugt1ΔIEC) and control (Ugt1F/F) mice are treated with dextran sulfate sodium (DSS) to induce acute colon inflammation and cell apoptosis. Corresponding with the in vitro data, western blot and TUNEL stain show lower protein expressions of P53, P21, BAX, caspase‐3 and less apoptotic cells in the colon of Ugt1ΔIEC mice. However, there is no difference in inflammatory response between Ugt1ΔIEC and Ugt1F/F samples. Moreover, the treatment of azoxymethane plus DSS causes higher tumor incidence and larger tumor size in the colon of Ugt1ΔIEC mice, suggesting that the inactivation of P53 mediated apoptosis increases colon tumorigenesis. In summary, our experiments verify that the presence of UGT1 in colon epithelial cells is important in the activation of P53 mediated apoptosis and protects normal tissue from neoplastic transformation.Grant Funding Source: Supported by US Public Health Service Grants R21CA171008, ES010337 and GM100481, Natural Science Foundation of China (Grants 91029746), and Chiha Scholarship Funding