The effect of radixin knockdown on the expression and efflux function of MRP2 in SGC-7901 cells

Abstract

Multidrug resistance-associated protein 2 (MRP2, ABCC2) is the second member of the MRP transporter family and functions physiologically as an organic anion transporter. Earlier studies have confirmed that radixin, which is a member of the ERM (ezrin/radixin/moesin) family, modulates MRP2 localization at the canalicular membrane in hepatocytes. The relationship between radixin and MRP2 – particularly, the effect of radixin on the expression and function of MRP2 in cells or tissues that co-express all three ERM proteins – has not been well studied. To examine the role of radixin in the expression and function of MRP2 and other MRPs, we chose human gastric carcinoma SGC-7901 cells that express all three ERM proteins rather than hepatocytes, which predominantly express radixin. Radixin stable knockdown SGC-7901 cells, which were constructed by RNAi, exhibited no compensatory up-regulation of ezrin or moesin. The mRNA expression profiles of MRPs in the radixin knockdown cells were primarily evaluated by RT-PCR. Real time quantitative RT-PCR and western blot analysis revealed that the radixin deficiency caused the mRNA and protein expression levels of MRP2 to be reduced by about 50%, respectively. Accordingly, efflux and MTT assays showed that the radixin knockdown cells exhibited lower efflux ability with respect to calcein but no significant change in cell viability. In conclusion, among the MRP1–6 family members, radixin selectively modulates the expression and function of MRP2 in a system co-expressing all three ERM proteins.