Decreased in situ insulin receptor dephosphorylation in hyperglycemia-induced insulin resistance in rat adipocytes.

Abstract

The regulation of insulin receptor (IR) tyrosine (tyr) phosphorylation is a key step in the control of insulin signaling. Augmented IR tyr dephosphorylation by protein tyrosine phosphatases (PTPs) may contribute to insulin resistance. To investigate this possibility in hyperglycemia-induced insulin resistance, primary cultured rat adipocytes were rendered insulin-resistant by chronic exposure (18 h) to 15 mmo/l glucose combined with 10(-7) mol/l insulin. Insulin-resistant adipocytes showed a decrease in insulin sensitivity and a maximum response of 2-deoxyglucose uptake, which was associated with a decrease in maximum insulin-stimulated IR tyr phosphorylation in situ. To assess tyr dephosphorylation, IRs of insulin-stimulated permeabilized adipocytes were labeled with [gamma-32P]ATP and chased for 2 min with unlabeled ATP in the presence of EDTA. In a nonradioactive protocol, insulin-stimulated adipocytes were permeabilized and exposed to EDTA and erbstatin for 2 min, and IRs were immunoblotted with anti-phosphotyrosine (pY) antibodies. Both methods showed a similar diminished extent of IR tyr dephosphorylation in resistant cells. Immunoblotting of four candidate IR-PTPs demonstrated no change in PTP1B or the SH2 domain containing phosphatase-2 (SHP-2), whereas a significant decrease in leukocyte antigen-related phosphatase (LAR) (51 +/- 3% of control) and an increase in PTP-alpha (165 +/- 16%) were found. Activity of immunoprecipitated PTPs toward a triple tyr phosphorylated IR peptide revealed a correlation with protein content for PTP1B, SHP-2, and LAR but a decrease in apparent specific activity of PTP-alpha. The data indicate that decreased IR tyr phosphorylation in hyperglycemia-induced insulin resistance is not due to enhanced dephosphorylation. The diminished IR tyr dephosphorylation observed in this model is associated with decreased LAR protein content and activity.

• Authors: S Tang, H Le-Tien, B J Goldstein, P Shin, R Lai, I G Fantus
• Journal: Diabetes (Diabetes) Vol. 50 Issue 1 Pg. 83-90 (Jan 2001) ISSN: 0012-1797 [Print] United States
• PMID: 11147799 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Phosphotyrosine
• Tyrosine
• Deoxyglucose
• Receptor, Insulin
• Protein Phosphatase 2
• Protein Tyrosine Phosphatases

Topics

• Adipocytes (metabolism)
• Animals
• Deoxyglucose (pharmacokinetics)
• Hyperglycemia (metabolism, physiopathology)
• Immunoblotting
• Insulin Resistance (physiology)
• Male
• Phosphorylation (drug effects)
• Phosphotyrosine (metabolism)
• Protein Phosphatase 2
• Protein Tyrosine Phosphatases (metabolism)
• Rats
• Rats, Sprague-Dawley
• Receptor, Insulin (metabolism)
• Tyrosine (metabolism)