Farnesoid X receptor induces GLUT4 expression through FXR response element in the GLUT4 promoter.

GLUT4, the main insulin-responsive glucose transporter, plays a critical role in maintaining systemic glucose homeostasis and is subject to complicated metabolic regulation. GLUT4 expression disorder might cause insulin resistance, and over-expression of GLUT4 has been confirmed to ameliorate diabetes. Here, we reported that farnesoid X receptor (FXR) and its agonist chenodeoxycholic acid (CDCA) could induce GLUT4 transcription in 3T3-L1 and HepG2 cells. Furthermore, CDCA could increase the GLUT4 protein amount in C57BL/6J mice sex-dependently. The following progressive 5'-deletion analysis and site-mutation investigation further suggested that FXR could induce GLUT4 expression through FXR response element (FXRE) in the GLUT4 promoter. EMSA and knock-down of retinoid X receptor (RXR) indicated that FXR binds to the GLUT4-FXRE as a monomer and RXR does not participate in the FXR stimulation of GLUT4 expression. In addition, we demonstrated that FXR does not interfere with insulin-induced GLUT4 translocation to plasma membrane. All these data thereby implied that FXR is a new transcription factor of GLUT4, further elucidating the potential role for FXR in glucose metabolism. Copyright 2008 S. Karger AG, Basel.