SHC MEDIATES IL-6 SIGNALING BY INTERACTING WITH GP130 AND JAK2 KINASE

IL-6 is a multifunctional cytokine involved in hemopoiesis, immune reg ulation, inflammation, neural development, and infection. IL-6 belongs to a family of related cytokines that includes leukemia inhibitory fa ctor, oncostatin M, IL-11, ciliary neurotropic factor, and cardiotropi n-1, all of which initiate signaling through a receptor-associated gp1 30. IL-6 induces homodimerization of gp130 and activates the Jak/STAT pathway of signal transduction. In addition, IL-6 stimulates the mitog en-activated protein kinases designated ERK (extracellular signal-regu lated kinase)-1 and -2. Activation of ERK-1 and -2 may involve the Src homology-2 containing proteins Shc and Grb2. Here we provide evidence that Shc could function as signaling molecules for IL-6 in DeFew-IL-6 R/gp130 cells, a human B lymphoma cell line engineered to express high levels of both the IL-6R (p80) and the gp130 subunit. IL-6 was shown to promote the rapid tyrosine phosphorylation of gp130, Jak2, and Shc proteins. Moreover, Shc associated both in vivo and in vitro with phos phorylated gp130 through the Shc-Src homology-2 domain. We also report that Shc bound to activated Jak2 by using the Shc amino terminal phos photyrosine interaction domain. Following IL-6 stimulation, Shc physic ally associated with Grb2. Thus, the data point to Shc proteins as a f unctional link between the Jak2 and Ras pathways of IL-6 signal transd uction.