Regulation and function of protein kinase B and MAP kinase activation by the IL-5/GM-CSF/IL-3 receptor

Interleukin (IL)-3, IL-5 and granulocyte-macrophage colony-stimulating fact or (GM-CSF) regulate proliferation, differentiation and apoptosis of target cells. Receptors for these cytokines consist of a cytokine-specific alpha subunit and a common shared beta c subunit, Tyrosine phosphorylation of the beta c is thought to play a critical role in mediating signal transduction events. We have examined the effect of mutation of beta c tyrosines on the activation of multiple signal transduction pathways. Activation of protein kinase B (PKB) required JAK2 and was inhibited by dominant-negative phosph atidylinositol 3-kinase (P13K). Overexpression of JAK2 was sufficient to ac tivate both protein kinase B (PKB) and extracellular regulated kinase-1 (ER K1). Tyrosine 577 and 612 were found to be critical for the activation of P KB and ERK1, but not activation of STAT transcription factors, Activation o f both PKB and ERK have been implicated in the regulation of proliferation and apoptosis. We generated GM-CSFR stable cell lines expressing receptor m utants to evaluate their effect on these processes. Activation of both PKB and ERK was perturbed, while STAT activation remained unaffected. Tyrosines 577 and 612 were necessary for optimal proliferation, however, mutation of these tyrosine residues did not affect GM-CSF mediated rescue from apoptos is. These data demonstrate that while phosphorylation of beta c tyrosine re sidues 577 and 612 are important for optimal cell proliferation, rescue fro m apoptosis can be mediated bg alternative signalling routes apparently ind ependent of PKB or ERK activation.