TY - JOUR T1 - Receptor for Activated C-Kinase 1 Regulates the Cell Surface Expression and Function of ATP Binding Cassette G2 JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 2320 LP - 2328 DO - 10.1124/dmd.110.034603 VL - 38 IS - 12 AU - Yuki Ikebuchi AU - Kousei Ito AU - Tappei Takada AU - Naohiko Anzai AU - Yoshikatsu Kanai AU - Hiroshi Suzuki Y1 - 2010/12/01 UR - http://dmd.aspetjournals.org/content/38/12/2320.abstract N2 - In a previous report, we identified the receptor for activated C-kinase 1 (RACK1) as a positive regulator of the cellular localization and expression of ATP-binding cassette B4, a phosphatidylcholine translocator expressed on the bile canalicular membrane. In the present study, we focused on the role of RACK1 on ATP-binding cassette G2 (ABCG2), which is responsible for the cellular extrusion of compounds including antitumor drugs. Protein expression of ABCG2 was up-regulated by RACK1 overexpression, although mRNA expression of ABCG2 was not dependent on RACK1. The effect of RACK1 on the expression of ABCG2 on the cell surface was confirmed by the uptake of [3H]estrone sulfate, an ABCG2 substrate, into isolated membrane vesicles. The expression of RACK1 affected cellular resistance to mitoxantrone, an anticancer drug excreted by ABCG2, and this effect of RACK1 was abolished in the presence of fumitremorgin C, a selective ABCG2 inhibitor. These results suggest that RACK1 has functional significance as a regulatory cofactor of ABCG2 and is indispensable for the cell surface expression and excretion function of ABCG2. The precise mechanism for RACK1-dependent expression of ABCG2 remains to be clarified, because the results of N-benzoyloxycarbonyl (Z)-Leu-Leu-leucinal (MG132) and chloroquine treatment and those of metabolic labeling experiments did not give us clear evidence whether the reduction of ABCG2 expression in RACK1-knocked down cells may be caused by the suppression of ABCG2 protein synthesis or by acceleration of its degradation. ER -