A novel pathway from phosphorylation of tyrosine residues 239/240 of Shc, contributing to suppress apoptosis by IL-3

Interleukin 3 (IL-3) not only induces DNA synthesis of haematopoietic cells but also maintains their viability by suppressing apoptosis. IL-3 stimulates tyrosine phosphorylation of the She adaptor protein and thereby formation of a complex of She with Grb2 at phosphorylated tyrosine (Y) residue 317-Shc. This pathway is implicated in Ras/mitogen-activated protein kinase (MAPK) activation towards c-fos gene expression. We examined the possible involvement of She in the anti-apoptotic activity of IL-3. Conditional overexpression of the She SH2 domain, a dominant-negative mutant of Shc, was found to induce apoptosis of IL-3-dependent Ba/F3 cells along with a reduction of c-myc gene expression. Apoptosis was rescued by the exogenously introduced c-myc gene. Since we identify novel tyrosine phosphorylation sites of She: Y239 and Y240, their role on cell survival was tested by mutational analysis. Ba/F3 cells expressing mutant She Y317F, which is unable to stimulate efficiently the Ras pathway, still showed resistance to apoptosis. However, cells expressing She Y239/240F, which is able to stimulate the Ras pathway, were sensitive to apoptosis. In these cells, induction of the c-myc gene was reduced. These findings suggest that a new signalling pathway for cell survival is generated from Y239/240 of She to the nuclei involving c-myc gene expression.