INTERFERON-ALPHA INDUCES RAPID TYROSINE PHOSPHORYLATION OF THE VAV PROTOONCOGENE PRODUCT IN HEMATOPOIETIC-CELLS

The vav proto-oncogene product (p95vav) is specifically expressed in c ells of the hematopoietic system, contains one Src homology 2 and two Src homology 3 domains, and is a substrate for receptor and non-recept or tyrosine kinases. Immunoblotting experiments using an anti-phosphot yrosine monoclonal antibody showed that interferon alpha (IFNalpha) in duces rapid tyrosine phosphorylation of p95vav after binding to its ce ll surface receptor in the U-266 human myeloma cell line. The IFNalpha -induced tyrosine phosphorylation of p950vav was time- and dose-depend ent, confirming the specificity of the process. IFNalpha-dependent tyr osine phosphorylation of p95vav was also observed in other hematopoiet ic cell lines of B-cell origin (Daudi), T-cell origin (MOLT-4), and pr omyelocytic origin (HL-60). Immunoprecipitation experiments performed with P-32-labeled U-266 cells and phosphoaminoacid analysis of the ban ds corresponding to p95vav showed that p95vav is phosphorylated on ser ine residues prior to IFNalpha stimulation of the cells. After IFNa st imulation significant amounts of phosphorylation of p95vav on tyrosine residues were detectable. Tyrosine phosphorylation of p95vav in U-266 and HL-60 cells was also induced by two other Type I IFNs, IFNbeta an d EFNomega. Altogether these data suggest that the vav proto-oncogene product is a substrate for a Type I IFN-regulated tyrosine kinase(s) a nd may be involved in the signal transduction pathway of Type I IFNs i n hematopoietic cells.