Expression of inducible membrane-anchored insulin receptor kinase enhances deoxyglucose uptake

We have transfected mouse L cells with a recombinant membrane-anchored insulin receptor kinase (called MARK), under the transcriptional control of a glucocorticoid-responsive element. The transfected construct includes only 15 extracellular residues, with the transmembrane and intracellular kinase domains of the human insulin receptor cDNA (amino acid residues -27 to 12 and 915 to 1343 (see Ullrich, A., Bell, J. R., Chen, E. Y., Herrera, R., Petruzzelli, L. M., Dull, T. J., Gray, A., Coussens, L., Liao, Y. C., Tsubokawa, M., Mason, A., Seeburg, P. H., Grunfeld, C., Rosen, O. M., and Ramachandran, J. (1985) Nature 313, 756-761), predicted Mr = 56,000 with signal sequence, 53,000 without). Transfected cells which are exposed to dexamethasone express two proteins of approximate Mr = 54,000 which (a) react with anti-peptide antisera raised to human insulin receptor sequences, (b) localize to the membrane fraction, and (c) possess ligand (insulin)-independent tyrosine kinase activity. In extracts of steroid-treated MARK cells, a phosphotyrosine-containing protein of Mr = 185,000 is detected, which corresponds in size to a known endogenous substrate for the insulin receptor. Control studies were performed with the nontransfected parent line, and with L cells transfected with an inactive human insulin receptor protein tyrosine kinase. Dexamethasone induced no change in the proteins detected by an anti-phosphotyrosine antibody in the two control lines. In studies of deoxyglucose uptake, dexamethasone stimulated increase in deoxyglucose uptake 2-fold in the MARK cells compared to the same cells studied in the absence of dexamethasone. Dexamethasone had no effect in the control cell lines. These studies demonstrate that a membrane-anchored insulin receptor kinase, devoid of virtually the entire extracellular domain of the insulin receptor, is sufficient to induce enhanced deoxyglucose uptake.