Oridonin inhibited the tyrosine kinase activity and induced apoptosis in human epidermoid carcinoma A431 cells

Oridonin, an active component isolated from the plant Rabdosia rubescens, has been reported to exhibit antitumor effects, but little is known about its molecular mechanism of action. In this study, we first investigated the mechanism involved in oridonin-induced cell death in human epidermoid carcinoma A431 cells, which overexpress epidermal growth factor receptor (EGFR). After treatment with various doses of oridonin for 24 h, the majority of A431 cells underwent apoptosis in a time- and dose-dependent manner as measured by an LDH activity-based assay. Treatment with oridonin at various concentrations for 24 h caused significant inhibition on the total tyrosine kinase activities and downregulation of EGFR expression or EGFR phosphorylation. Oridonin significantly affected the localization of EGFR and phosphorylated EGFR on the cell membrane. However, genistein (a well-known tyrosine kinase inhibitor) did not induce apoptotic A431 cell death. Importantly, oridonin exhibited much stronger inhibitory effect on the total tyrosine kinase activities or EGFR tyrosine phosphorylation as well as much stronger suppression on EGFR and phosphorylated EGFR localization than genistein in A431 cells. Taken together, oridonin exerted a potential inhibitory effect on the tyrosine kinase activity of A431 cells. The decrease in the tyrosine kinase activity and the blockage of EGFR tyrosine phosphorylation might be one of the causes of oridonin-induced A431 cell death.