SUBSTITUTION OF THE ERBB-2 ONCOPROTEIN TRANSMEMBRANE DOMAIN ACTIVATESTHE INSULIN-RECEPTOR AND MODULATES THE ACTION OF INSULIN AND INSULIN-RECEPTOR SUBSTRATE-1

The mechanism through which insulin binding to the extracellular domai n of the insulin receptor activates the intrinsic tyrosine kinase in t he intracellular domain of the protein is unknown. For the c-neu/erbB- 2 (c-erbB-2) protooncogene, a single point mutation within the transme mbrane (TM) domain converting Val-664 to Glu (erbB-2V-->E) results in elevated levels of tyrosine kinase activity and cellular transformatio n. We report the construction of a chimeric insulin receptor in which the TM domain of the receptor has been substituted with that encoded b y erbB-2V-->E. When expressed in Chinese hamster ovary cells this chim eric receptor displays maximal levels of autophosphorylation and kinas e activity in the absence of insulin. This activity results in an incr ease in the level of insulin-receptor substrate 1 phosphorylation but a down-regulation in insulin-receptor substrate 1 protein and desensit ization to insulin stimulation of glycogen synthesis. By contrast, bas al levels of DNA synthesis are elevated to levels almost-equal-to 60% of those observed in serum-stimulated cells. Over-expression of chimer ic insulin receptors containing the c-erbB-2 TM domain or a single poi nt mutation in the insulin receptor TM domain of Val-938-->Asp, on the other hand, shows none of these alterations. Thus, the TM domain enco ded by erbB-2V-->E contains structural features that can confer ligand -independent activation in a heterologous protein. Constitutive activa tion of the insulin receptor results in a relative increase in basal l evels of DNA synthesis, but an apparent resistance to the metabolic ef fects of insulin.