Regulation of the Src homology 2-containing inositol 5-phosphatase SHIP1 in HIP1/PDGF beta R-transformed cells

It has been shown previously that the Huntingtin interacting protein 1 gene (HIP1) was fused to the platelet-derived growth factor beta receptor gene (PDGF betaR) in leukemic cells of a patient with chronic myelomonocytic leu kemia. This resulted in the expression of the chimeric HIP1/PDGF betaR prot ein, which oligomerizes, is constitutively tyrosine-phosphorylated, and tra nsforms the Ba/F3 murine hematopoietic cell line to interleukin-3-independe nt growth. Tyrosine phosphorylation of a 130-kDa protein (p130) correlates with transformation by HIP1/PDGF betaR and related transforming mutants. We report here that the p130 band is immunologically related to the 125-kDa i soform of the Src homology 2-containing inositol B-phosphatase, SHIP1. We h ave found that SHIP1 associates and colocalizes with the HIP1/ PDGF betaR f usion protein and related transforming mutants, These mutants include a mut ant that has eight Src homology 2-binding phosphotyrosines mutated to pheny lalanine, In contrast, SHIP1 does not associate with WP(KI), the kinase-dea d form of HIP1/PDGF betaR. We also report that phosphorylation of SHIP1 by HIP1/PDGF betaR does not change its 5-phosphatase-specific activity. This s uggests that phosphorylation and possible PDGF betaR-mediated sequestration of SHIP1 from its substrates (PtdIns(3,4,5)P-3 and Ins(1,3,4,5)P-4) might alter the levels of these inositol-containing signal transduction molecules , resulting in activation of downstream effecters of cellular proliferation and/or survival.