Monoclonal antibodies to the insulin receptor mimic metabolic effects of insulin but do not stimulate receptor autophosphorylation in transfected NIH 3T3 fibroblasts

Transcriptional stimulation of the delta 1-crystallin gene by insulin-like growth factor I and insulin requires DNA cis elements in chicken

Insulin-like growth factor I (IGF-I) and insulin regulate expression of the endogenous delta 1-crystallin gene in embryonic lens cells that express receptors for both peptides. To further analyze the transcriptional component of this hormonal effect, transient transfections of lens cells were prepared with DNA constructs containing deletions of the delta 1-crystallin promoter and the chloramphenicol acetyltransferase reporter gene. A 77-nucleotide DNA segment of the delta 1-crystallin promoter from nucleotide positions-120 to -43 confers sensitivity to insulin and IGF-I. The hormonal effect is dose-dependent, and maximal stimulation of promoter activity (2- to 2.5-fold induction) is obtained with 10(-8) M IGF-I and 10(-7) M insulin. Mobility-shift DNA-binding analysis shows specific binding of nuclear protein(s) to the delta 1-crystallin promoter DNA between positions -120 and +23, which appears to be regulated by IGF-I. An SP1-binding motif is involved in this DNA-protein interaction. The bivalent IgG fraction of an anti-insulin receptor antiserum (B-10), known to mimic insulin action in other systems, stimulates promoter activity to the same extent as insulin.

Wheat-germ agglutinin mimics metabolic effects of insulin without increasing receptor autophosphorylation

Expression of insulin metabolic effects can be obtained by anti-receptor antibodies without activation of the tyrosine kinase activity [O'Brien R. M., Soos M. A. and Siddle K. (1987) EMBO J. 6, 4003-4010; Forsayeth J. R., Caro J. F., Sinha M. K., Maddux B. A. and Goldfine I. D. (1987) Proc. natn. Acad. Sci. U.S.A. 84, 34,448-34,514; Ponzio G., Contreres J. O., Debant A., Baron V., Gautier N., Dolais-Kitabgi J. and Rossi B. (1988) EMBO J. 7, 4111-4117; Hawley D. M., Maddux B. A., Patel R. G., Wong K. Y., Mamula P. W., Firestone G. L., Brunetti A., Verspohl E. and Goldfine I. D. (1989) J. biol. Chem. 264, 2438-2444; Soos M. A., O'Brien R. M., Brindle N. P. J., Stigter J. M., Okamoto A. K., Whittaker J. and Siddle K. (1989) Proc. natn. Acad. Sci. U.S.A. 86, 5217-5221.]. Recently, we have proposed that receptor cross-linking is sufficient in itself to stimulate glycogen synthesis, even if aggregation was performed on receptors mutated on Tyr 1162 and Tyr 1163 and thus devoid of tyrosine kinase activity [Debant A., Ponzio G., Clauser E., Contreres J. O. and Rossi B. (1989) Biochemistry 28, 14-17]. The aim of this study was to gain information on the involvement of receptor clustering in the expression of the different insulin biological effects. To this end, we studied the mimetic effects of wheat-germ agglutinin, which is likely to induce receptor aggregation without interacting with the receptor protein moiety. Wheat-germ agglutinin failed to promote DNA synthesis, whereas the lectin behaved as a potent mimicker of insulin on tyrosine aminotransferase activity and amino-acid transport. However, this stimulatory effect did not parallel the activation of receptor autophosphorylation. Our data reinforce the idea that the expression of the metabolic effects of insulin are not strictly dependent on a general tyrosine kinase activation.