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Am J Physiol Endocrinol Metab (September 27, 2005). doi:10.1152/ajpendo.00314.2005
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Submitted on July 12, 2005
Accepted on September 20, 2005

Exercise does not alter subcellular localization, but increases phosphorylation of insulin signaling proteins in human skeletal muscle

Chris Wilson1, Mark Hargreaves2, and Kirsten F Howlett1*

1 Center for Physical Activity and Nutrition (C-PAN), School of Exercise and Nutrition Sciences, Deakin University, Burwood, Victoria, Australia
2 Center for Physical Activity and Nutrition (C-PAN), School of Exercise and Nutrition Sciences, Deakin University, Burwood, Victoria, Australia; Department of Physiology, The University of Melbourne, Parkville, Victoria, Australia

* To whom correspondence should be addressed. E-mail: kirsten.howlett{at}deakin.edu.au.

The subcellular localization of insulin signaling proteins is altered by various stimuli such as insulin, IGF-1 and oxidative stress, and is thought to be an important mechanism that can influence intracellular signal transduction and cellular function. This study examined the possibility that exercise may also alter the subcellular localization of insulin signaling proteins in human skeletal muscle. Nine untrained males performed 60 min of cycling exercise (~67% VO2peak). Muscle biopsies were sampled at rest, immediately following exercise and 3 hours post-exercise. Muscle was fractionated by centrifugation into crude fractions; cytosolic, nuclear, and a high speed pellet containing membrane and cytoskeletal components. Fractions were analysed for protein content of insulin receptor, insulin receptor substrate (IRS)-1 and -2, p85 subunit of phosphatidylinositol 3-kinase, Akt and glycogen synthase kinase-3 (GSK-3). There was no significant change in the protein content of the insulin signaling proteins in any of the crude fractions following exercise or 3 hours post-exercise. Exercise had no significant effect on the phosphorylation of IRS-1 Tyr612 in any of the fractions. In contrast, exercise increased (P<0.05) the phosphorylation of Akt Ser473 and GSK-3{alpha}/{beta} Ser9/21 in the cytosolic fraction only. In conclusion, exercise can increase phosphorylation of downstream insulin signaling proteins specifically in the cytosolic fraction, but does not result in changes in the subcellular localization of insulin signaling proteins in human skeletal muscle. Change in the subcellular protein localization is therefore an unlikely mechanism to influence signal transduction pathways and cellular function in skeletal muscle following exercise.




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