EGF-induced inhibition of glucose transport is mediated by PKC and MAPK signal pathways in primary cultured chicken hepatocytes

Abstract

EGF is a regulator of a wide variety of processes in various cell systems. Hepatocytes are important sites in the body's metabolism and function. Glucose transporter 2 (GLUT2) is a major transporter that is expressed strongly in hepatocytes. Therefore, this study examined the effect of EGF on GLUT2 and its related signal cascades in primary cultured chicken hepatocytes. EGF decreased [(3)H]deoxyglucose uptake in a dose- and time-dependent manner (>10 ng/ml, 2 h). AG-1478 (an EGF receptor antagonist) and genistein and herbimycin A (tyrosine kinase inhibitors) blocked the EGF-induced decrease in [(3)H]deoxyglucose uptake, which correlated with the GLUT2 expression level. In addition, the EGF-induced decrease in GLUT2 protein expression was inhibited by staurosporine, H-7, or bisindolylmaleimide I (PKC inhibitors), PD-98059 (a MEK inhibitor), SB-203580 (a p38 MAPK inhibitor), and SP-600125 (a JNK inhibitor), suggesting a role of both PKC and MAPKs (p44/42 MAPK, p38 MAPK, and JNK). In particular, EGF increased the translocation of PKC isoforms (PKC-alpha, -beta(1), -gamma, -delta, and -zeta) from the cytosol to the membrane fraction and increased the activation of p44/42 MAPK, p38 MAPK, and JNK. Moreover, PKC inhibitors blocked the EGF-induced phosphorylation of three MAPKs. In conclusion, EGF decreases the GLUT2 expression level via the PKC-MAPK signal cascade in chicken hepatocytes.