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Inhibition of glucokinase translocation by AMP-activated protein kinase is associated with phosphorylation of both GKRP and 6-phosphofructo-2-kinase/ fructose-2,6-bisphosphatase

Lookup NU author(s): Mohammed Mukhtar, Victoria Payne, Dr Catherine Arden, Dr Andrew Harbottle, Professor Loranne Agius

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Abstract

The rate of glucose phosphorylation in hepatocytes is determined by the subcellular location of glucokinase and by its association with its regulatory protein (GKRP) in the nucleus. Elevated glucose concentrations and precursors of fructose 1-phosphate (e.g., sorbitol) cause dissociation of glucokinase from GKRP and translocation to the cytoplasm. In this study, we investigated the counter-regulation of substrate-induced translocation by AICAR (5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside), which is metabolized by hepatocytes to an AMP analog, and causes activation of AMP-activated protein kinase (AMPK) and depletion of ATP. During incubation of hepatocytes with 25 mM glucose, AICAR concentrations below 200 μM activated AMPK without depleting ATP and inhibited glucose phosphorylation and glucokinase translocation with half-maximal effect at 100-140 μM. Glucose phosphorylation and glucokinase translocation correlated inversely with AMPK activity. AICAR also counteracted translocation induced by a glucokinase activator and partially counteracted translocation by sorbitol. However, AICAR did not block the reversal of translocation (from cytoplasm to nucleus) after substrate withdrawal. Inhibition of glucose-induced translocation by AICAR was greater than inhibition by glucagon and was associated with phosphorylation of both GKRP and the cytoplasmic glucokinase binding protein, 6-phosphofructo-2-kinase/fructose-2,6- bisphosphatase (PFK2) on ser-32. Expression of a kinase-active PFK2 variant lacking ser-32 partially reversed the inhibition of translocation by AICAR. Phosphorylation of GKRP by AMPK partially counteracted its inhibitory effect on glucokinase activity, suggesting altered interaction of glucokinase and GKRP. In summary, mechanisms downstream of AMPK activation, involving phosphorylation of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase and GKRP are involved in the ATP-independent inhibition of glucose-induced glucokinase translocation by AICAR in hepatocytes. Copyright © 2008 the American Physiological Society.


Publication metadata

Author(s): Mukhtar MH, Payne VA, Arden C, Harbottle A, Khan S, Lange AJ, Agius L

Publication type: Article

Publication status: Published

Journal: American Journal of Physiology: Regulatory, Integrative and Comparative Physiology

Year: 2008

Volume: 294

Issue: 3

Pages: R766-R774

ISSN (print): 0363-6119

ISSN (electronic): 1522-1490

Publisher: American Physiological Society

URL: http://dx.doi.org/10.1152/ajpregu.00593.2007

DOI: 10.1152/ajpregu.00593.2007


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