A GSK-3/TSC2/mTOR pathway regulates glucose uptake and GLUT1 glucose transporter expression

Carolyn L. Buller, Robert D. Loberg, Ming Hui Fan, Qihong Zhu, James L. Park, Eileen Vesely, Ken Inoki, Kun Liang Guan, Frank C. Brosius

Research output: Contribution to journalArticlepeer-review

168 Scopus citations

Abstract

Glucose transport is a highly regulated process and is dependent on a variety of signaling events. Glycogen synthase kinase-3 (GSK-3) has been implicated in various aspects of the regulation of glucose transport, but the mechanisms by which GSK-3 activity affects glucose uptake have not been well defined. We report that basal glycogen synthase kinase-3 (GSK-3) activity regulates glucose transport in several cell types. Chronic inhibition of basal GSK-3 activity (8-24 h) in several cell types, including vascular smooth muscle cells, resulted in an approximately twofold increase in glucose uptake due to a similar increase in protein expression of the facilitative glucose transporter 1 (GLUT1). Conversely, expression of a constitutively active form of GSK-3β resulted in at least a twofold decrease in GLUT1 expression and glucose uptake. Since GSK-3 can inhibit mammalian target of rapamycin (mTOR) signaling via phosphorylation of the tuberous sclerosis complex subunit 2 (TSC2) tumor suppressor, we investigated whether chronic GSK-3 effects on glucose uptake and GLUT1 expression depended on TSC2 phosphorylation and TSC inhibition of mTOR. We found that absence of functional TSC2 resulted in a 1.5-to 3-fold increase in glucose uptake and GLUT1 expression in multiple cell types. These increases in glucose uptake and GLUT1 levels were prevented by inhibition of mTOR with rapamycin. GSK-3 inhibition had no effect on glucose uptake or GLUT1 expression in TSC2 mutant cells, indicating that GSK-3 effects on GLUT1 and glucose uptake were mediated by a TSC2/mTOR-dependent pathway. The effect of GSK-3 inhibition on GLUT1 expression and glucose uptake was restored in TSC2 mutant cells by transfection of a wild-type TSC2 vector, but not by a TSC2 construct with mutated GSK-3 phosphorylation sites. Thus, TSC2 and rapamycin-sensitive mTOR function downstream of GSK-3 to modulate effects of GSK-3 on glucose uptake and GLUT1 expression. GSK-3 therefore suppresses glucose uptake via TSC2 and mTOR and may serve to match energy substrate utilization to cellular growth.

Original languageEnglish (US)
Pages (from-to)C836-C843
JournalAmerican Journal of Physiology - Cell Physiology
Volume295
Issue number3
DOIs
StatePublished - Sep 2008
Externally publishedYes

Keywords

  • Cell signaling
  • Glycogen synthetase kinase
  • Mammalian target of rapamycin
  • Metabolism
  • S6 kinase
  • Tuberous sclerosis complex

ASJC Scopus subject areas

  • Physiology
  • Cell Biology

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