Identification of a novel immunoreceptor tyrosine-based activation motif-containing molecule, STAM2, by mass spectrometry and its involvement in growth factor and cytokine receptor signaling pathways

In an effort to clone novel tyrosine-phosphorylated substrates of the epide rmal growth factor receptor, we have initiated an approach coupling affinit y purification using anti-phosphotyrosine antibodies to mass spectrometry-b ased identification, Here, we report the identification of a signaling mole cule containing a Src homology 3 domain as well as an immunoreceptor tyrosi ne-based activation motif (ITAM). This molecule is 55% identical to a previ ously isolated molecule designated signal transducing adaptor molecule (STA M) that was identified as an interleukin (IL)-2-induced phosphoprotein and is therefore designated STAM2, Tyrosine phosphorylation of STAM2 is induced by growth factors such as epidermal growth factor and platelet-derived gro wth factor as well as by cytokines like IL-3. Several of the deletion mutan ts tested except the one containing only the amino-terminal region underwen t tyrosine phosphorylation upon growth factor stimulation, implying that ST AM2 is phosphorylated on several tyrosine residues, STAM2 is downstream of the Jak family of kinases since coexpression of STAM2 with Jak1 or Jak2 but not an unrelated Tec family kinase, Etk, resulted in its tyrosine phosphor ylation, In contrast to epidermal growth factor receptor-induced phosphoryl ation, this required the ITAM domain since mutants lacking this region did not undergo tyrosine phosphorylation, Finally, overexpression of wild type STAM2 led to an increase in IL-8-mediated induction of c-Myc promoter activ ation indicating that it potentiates cytokine receptor signaling.