Insulin resistance is characteristic of many patients with
polycystic ovary syndrome (PCOS). Several studies have suggested that a decrease in
insulin receptor (IR) autophosphorylation is a significant component of this resistance. In this study, we have used a highly sensitive ELISA to measure IR
tyrosine phosphorylation in fibroblasts from patients with PCOS and healthy control women. After the stimulation of intact fibroblasts with
insulin, IR
tyrosine phosphorylation in cells from the PCOS patients was decreased by approximately 40% when compared with controls. However, when IR were first immunocaptured from fibroblasts and then stimulated with
insulin, neither basal nor
insulin-stimulated IR autophosphorylation was different between the two groups, suggesting that
a factor independent of the IR was involved. To examine the role of increased
serine kinase activity in decreased IR autophosphorylation in PCOS, fibroblasts from PCOS patients were pretreated with inhibitors of
serine kinases before
insulin stimulation. Pretreatment with H7, a nonspecific
protein kinase inhibitor, completely reversed the decrease in
insulin-stimulated IR autophosphorylation. Pretreatment with
H89, an inhibitor of
protein kinase A, partially reversed this function, whereas pretreatment with
Gö6983, an inhibitor of
protein kinase C, was without effect. We next studied the effects of two small molecule activators of the IR
tyrosine kinase: TLK16998 and Merck L7. Both TLK16998 and Merck L7 were able to reverse the impaired
insulin-stimulated IR autophosphorylation. In summary,
a factor(s) extrinsic to the IR cause impaired IR signaling in fibroblasts from patients with PCOS. Reversal of the impaired IR signaling by inhibitors of
serine kinase activity suggests that
serine kinase-mediated pathways may be involved in the
insulin resistance. Moreover, the observation that TLK16998 and Merck L7 improved IR
tyrosine phosphorylation in fibroblasts from patients with PCOS suggests that specific pharmacological
therapies might be developed to treat the
insulin resistance in PCOS.