Mutation of tyrosine 960 within the insulin receptor juxtamembrane domain impairs glucose transport but does not inhibit ligand-mediated phosphorylation of insulin receptor substrate-2 in 3T3-L1 adipocytes

CSF-1 is equipotent to insulin in its ability to stimulate 2[H-3]deoxygluco se uptake in 3T3-L1 adipocytes expressing the colony stimulating factor-1 r eceptor/insulin receptor chimera (CSF1R/IR), However, CSF-1-stimulated gluc ose uptake and glycogen synthesis is reduced by 50% in comparison to insuli n in 3T3-L1 cells expressing a CSF1R/IR mutated at Tyr(960) (CSF1R/IRA960), CSF-1-treated adipocytes expressing the CSF1R/IRA960 were impaired in thei r ability to phosphorylate insulin receptor substrate 1 (IRS-1) but not in their ability to phosphorylate IRS-2, Immunoprecipitation of IRS proteins f ollowed by Western blotting revealed that the intact CSF1R/IR co-precipitat es with IRS-2 from CSF-1-treated cells. In contrast, the CSF1R/IRA960 co-pr ecipitates poorly with IRS-S, These observations suggest that Tyr(960) is i mportant for interaction of the insulin receptor cytoplasmic domain with IR S-2, but it is not essential to the ability of the insulin receptor tyrosin e kinase to use IRS-2 as a substrate. These observations also suggest that in 3T3-L1 adipocytes, tyrosine phosphorylation of IRS-2 by the insulin rece ptor tyrosine kinase is not sufficient for maximal stimulation of receptor- regulated glucose transport or glycogen synthesis.