Radixin influences the changes in the small intestinal P-glycoprotein by etoposide treatment

Previously, we reported that repeated oral administration of etoposide (ETP) increases P-glycoprotein (P-gp) expression in association with activation of ezrin/radixin/moesin (ERM) in the small intestine. Radixin has recently attracted attention for its critical role in the plasma membrane localization of certain drug transporters including P-gp by working as a scaffold protein. However, there have been no report investigating that radixin really interacts with small intestinal P-gp and is involved in the mechanism by which the levels of P-gp are altered. Here, we examined whether radixin is involved in the increased P-gp expression in the small intestine after ETP treatment. Repeated oral treatment with ETP (10 mg/kg/day) for 7 d significantly increased ERM proteins bound to P-gp in the small intestine as determined by immunoprecipitation analysis. In particular, radixin but not ezrin or moesin bound to P-gp was dramatically increased in association with the up-regulation of P-gp in the small intestinal membrane, and radixin was highly co-localized with P-gp as measured by immunofluorescence analysis. In conclusion, radixin may contribute, at least in part, to an increase in the expression of the small intestinal P-gp upon induction with repeated oral treatment with ETP.