Rac-dependent anti-apoptotic signaling by the insulin receptor cytoplasmic domain

Mutations in the cytoplasmic domain of the insulin receptor that block the ability of the receptor to stimulate glucose uptake do not block the receptor's ability to inhibit apoptosis (Boehm, J. E., Chaika, O. V., and Lewis, R. E. (1998) J. Biol. Chem. 273, 7169-7176). To characterize this survival pathway we used a chimeric receptor (CSF1R/IR) consisting of the ligand-binding domain of the colony-stimulating factor-1 receptor spliced to the cytoplasmic domain of the insulin receptor and a mutated version of the chimetic receptor containing a 12-amino acid deletion of the juxtamembrane domain (CSF1R/IRΔ960). In addition to the inhibition of apoptosis, activation of either the CSF1R/IR or the CSF1R/IRΔ960 rapidly induced membrane ruffling in Rat1 fibroblasts. The small GTPase Rac mediates membrane ruffling. Activated and dominant-inhibitory mutants of Rac and other small GTPases were expressed in Rat1 fibroblasts to examine a potential link between the intracellular pathways that induce membrane ruffling and promote cell survival. The anti-apoptotic action of the CSF1R/IRΔ960 was reversed by dominant-inhibitory Rac(N17), but not by Ras(N17) or Cdc42(N17). Activated Rac(V12), but not Ras(D12) or Cdc42(V12), promoted cell survival in the absence of insulin. These data implicate Rac as a mediator of an unique anti- apoptotic signaling pathway activated by the insulin receptor cytoplasmic domain.