Rescuing 3T3-L1 adipocytes from insulin resistance induced by stimulation of Akt-mammalian target of rapamycin/p70 S6 kinase (S6K1) pathway and serine phosphorylation of insulin receptor substrate-1: effect of reduced expression of p85alpha subunit of phosphatidylinositol 3-kinase and S6K1 kinase.

Abstract

Phosphorylation of insulin receptor substrate-1 (IRS-1) on serine residues has been recognized as a mechanism responsible for a diminution of insulin action and insulin resistance. Potential approaches to improve insulin sensitivity may include interference with and/or reduction in expression of certain signaling intermediates that participate in the pathogenesis of insulin resistance. In this study, we transduced fully differentiated 3T3-L1 adipocytes with a constitutively active myristoylated Akt that led to hyperactivation of mammalian target of rapamycin and p70 S6 kinase (S6K1), increased serine phosphorylation of IRS-1, and reduction in insulin-stimulated phosphatidylinositol (PI) 3-kinase activity and glucose transport. We then reduced expression of the PI 3-kinase regulatory subunit, p85alpha, or expression of S6K1 kinase using small interfering RNA transfections, which led to a reduction in p85alpha expression of 70% at 48 h (P < 0.05) and S6K1 of 49% (P < 0.05). Reduction in expression of either p85alpha or S6K1 achieved with small interfering RNA in the presence of myristoylated Akt rescued 3T3-L1 adipocytes from the insulin resistance induced by serine phosphorylation of IRS-1 and completely restored insulin-stimulated activation of PI 3-kinase and glucose uptake. We conclude that reduction in expression of p85alpha or S6K1 could represent therapeutic targets to mitigate insulin resistance.

• Authors: Rebecca Adochio, J Wayne Leitner, Reed Hedlund, Boris Draznin
• Journal: Endocrinology (Endocrinology) Vol. 150 Issue 3 Pg. 1165-73 (Mar 2009) ISSN: 1945-7170 [Electronic] United States
• PMID: 18948408 (Publication Type: Evaluation Study, Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.)

Chemical References

• Insulin Receptor Substrate Proteins
• Irs1 protein, mouse
• Phosphoinositide-3 Kinase Inhibitors
• Protein Subunits
• RNA, Small Interfering
• Serine
• Protein Kinases
• mTOR protein, mouse
• Oncogene Protein v-akt
• Ribosomal Protein S6 Kinases, 90-kDa
• Rps6ka1 protein, mouse
• TOR Serine-Threonine Kinases

Topics

• 3T3-L1 Cells
• Adipocytes (drug effects, metabolism, pathology)
• Animals
• Genetic Therapy (methods)
• Insulin Receptor Substrate Proteins (metabolism)
• Insulin Resistance (genetics, physiology)
• Mice
• Oncogene Protein v-akt (genetics, metabolism)
• Phosphatidylinositol 3-Kinases (metabolism, physiology)
• Phosphoinositide-3 Kinase Inhibitors
• Phosphorylation (genetics)
• Protein Kinases (metabolism)
• Protein Subunits (metabolism, physiology)
• RNA, Small Interfering (pharmacology)
• Ribosomal Protein S6 Kinases, 90-kDa (antagonists & inhibitors, metabolism)
• Serine (metabolism)
• Signal Transduction (genetics)
• TOR Serine-Threonine Kinases
• Transfection