Insulin resistance is associated with abnormal dephosphorylation of a synthetic phosphopeptide corresponding to the major autophosphorylation sites of the insulin receptor.
Insulin resistance in the ob/ob mouse model is associated with a reduction in insulin-induced protein-tyrosine phosphorylation in tissues such as liver. To ascertain whether this decrease in phosphorylation may be due to increased phosphatase activity, protein-tyrosine phosphatase (PTPase) activity was determined in particulate and soluble fractions from livers of 5- to 23-week-old ob/ob mice and age-matched lean littermates. PTPase activity was measured using a synthetic phosphopeptide, TRDIY(P)ETDY(P)Y(P)RK, as the substrate, corresponding to residues 1142 to 1153 of the insulin receptor and containing the major autophosphorylation sites of the regulatory domain. The ob/ob mice were hyperinsulinemic across all age groups, but only the youngest mice (aged 5 to 7 weeks) were hyperglycemic. Most PTPase activity was present in the liver particulate fraction and was 19% to 114% greater in ob/ob mice as compared with controls. PTPase activity in the liver soluble fraction was 26% less than control values in the youngest ob/ob mice (5 to 7 weeks), but increased with age and was 41% and 131% above control values at 21 to 23 and 25 to 27 weeks of age, respectively. Oral administration of the PTPase inhibitor sodium orthovanadate (0.6 mg/mL in drinking water for 2 weeks) to young ob/ob mice caused a significant reduction in the elevated particulate PTPase activity, with concomitant decreases in plasma insulin and plasma glucose. Assessment of PTPase activity with a monophosphate form of the same synthetic peptide, TRDIY(P)ETDYYRK, showed lower PTPase activities as compared with the triphosphate form and no significant differences between ob/ob and control preparations.(ABSTRACT TRUNCATED AT 250 WORDS)
Sredy
J
J
Wyeth-Ayerst Research, Princeton, NJ 08543-8000, USA.
Sawicki
D R
DR
Flam
B R
BR
Sullivan
D
D
D000595:Amino Acid Sequence; D000818:Animals; D001786:Blood Glucose / Q000032:analysis; D004195:Disease Models, Animal; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance / Q000502:physiology*; D008099:Liver / Q000201:enzymology; D008137:Longitudinal Studies; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008820:Mice, Obese; D008969:Molecular Sequence Data; D009765:Obesity / Q000378:metabolism*; D010748:Phosphopeptides / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D017027:Protein Tyrosine Phosphatases / Q000032:analysis / Q000378:metabolism / Q000502:physiology; D011972:Receptor, Insulin / Q000378:metabolism*; D014638:Vanadates / Q000494:pharmacology
D001786:Blood Glucose; D007328:Insulin; D010748:Phosphopeptides; D014638:Vanadates; D011972:Receptor, Insulin; D017027:Protein Tyrosine Phosphatases