Korean J Physiol Pharmacol.  2000 Dec;4(6):497-506.

GLUT phosphorylation may be required to GLUT translocation mechanism

Affiliations
  • 1Department of Physiology, College of Medicine, Ewha Womans University, 911-1 Mok Dong, Yang Chun Gu, Seoul, South Korea. jshah@mm.ewha.ac.kr

Abstract

In this work, GLUTs phosphorylations by a downstream effector of PI3-kinase, PKC- zeta, were studied, and GLUT4 phosphorylation was compared with GLUT2 phosphorylation in relation to the translocation mechanism. Prior to phosphorylation experiment, PKC- zeta kinase activity was determined as 20.76+/-4.09 pmoles Pi/min/25 ng enzymes. GLUT4 was phosphorylated by PKC- zeta and the phosphorylation was increased on the vesicles immunoadsorpted from LDM and on GLUT4 immunoprecipitated from GLUT4-contianing vesicles of adipocytes treated with insulin. However, GLUT2 in hepatocytes was neither phosphorylated by PKC- zeta nor changed in response to insulin treatment. It was confirmed by measuring the subcellular distribution of GLUT2 based on GLUT2 immunoblot density among the four membrane fractions before and after insulin treatment. Total GLUT2 distributions at PM, LYSO, HDM and LDM were 37.7+/-12.0%, 42.4+/-12.1%, 19.2+/-5.0% and 0.7+/-1.2% in the absence of insulin. Total GLUT2 distribution in the presence of insulin was almost same as that in the absence of insulin. Present data with previous findings suggest that GLUT4 translocation may be attributed to GLUT4 phosphorylation by PKC- zeta but GLUT2 does not translocate because GLUT2 is not phosphorylated by the kinase. Therefore, GLUT phosphorylation may be required in GLUT translocation mechanism.

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