ROLE OF THE VAV PROTOONCOGENE PRODUCT (VAV) IN ERYTHROPOIETIN-MEDIATED CELL-PROLIFERATION AND PHOSPHATIDYLINOSITOL 3-KINASE ACTIVITY

The vav proto-oncogene product (Vav), which is specifically expressed in hematopoietic cells, contains multiple structural motifs commonly u sed by intracellular signaling molecules, Although a variety of stimul i including erythropoietin (Epo) have been shown to tyrosine phosphory late Vav, little is known about the Vav signal transduction pathway. H ere, we have investigated the role of Vav in the Epo signaling pathway by characterizing its interaction with other proteins, using the huma n Epo-responsive cell line, F-36P, Immunoprecipitation and immunoblot analyses have demonstrated that Vav was associated with the Epo recept or (EpoR) in an Epo-independent manner and was tyrosine-phospho rylate d after Epo stimulation, Furthermore, two phosphotyrosine proteins (pp 70 and pp100) co-immunoprecipitated with the regulatory subunit of pho sphatidylinositol 3-kinase (PI3-kinase) (p85) were identified as EpoR and Vav, respectively. The interaction between Vav and p85 was shown t o be mediated through the SH2 domains of p85 by an in vitro binding as say and confirmed by the presence of in vitro PI3-kinase activity asso ciated with Vav, Treatment of the cells with antisense-vav and -p85 ab rogated Epo induced cell proliferation and PI3-kinase activity, Finall y, we found that JAK2 was associated with Vav in vivo and that Vav cou ld be tyrosine-phosphorylated by activated JAK2 in vitro, These result s suggest the possible role of JAK2 for tyro sine phosphorylation of V av and involvement of Vav and PI3-kinase in Epo-induced proliferative signals.