A novel spliced form of SH2-containing inositol phosphatase is expressed during myeloid development

SH2-containing Inositol Phosphatase (SHIP) is a 145 kD protein expressed in hematopoietic cells. SHIP is phosphorylated on tyrosine after receptor bin ding by several cytokines and has a negative role in hematopoiesis. We clon ed a murine complementary DNA (cDNA) sequence for an isoform of SHIP with a n internal 183 nucleotide deletion, encoding a protein 61 amino acids short er than 145 kD SHIP. This deletion eliminates potential SH3-domain binding regions and a potential binding site for the p85 subunit of Phosphatidylino sitol 3-Kinase. Using polyclonal anti-SHlP antibodies, we and of hers have previously observed a 135 kD SHIP isoform that is coexpressed with 145 kD S HIP. Here, we used monoclonal antibodies raised against the region deleted in the spliced form to show that the product of the novel spliced SHIP cDNA is antigenically identical to the 135 kD SHIP isoform. Like 145 kD SHIP, 1 35 kD SHIP expression was induced on differentiation of bone marrow cells. After macrophage colony-stimulating factor (M-CSF) stimulation of FDC-P1(Fm s) myeloid cells, both 145 and 135 kD SHIP forms were tyrosine phosphorylat ed and could be coimmunoprecipitated with antibodies to Shc and Grb2. Howev er, experiments showed only a weak association of 135 kD SHIP with p85. A p otentially analogous 135 kD SHIP species also appears in human differentiat ed leukocytes. (C) 1999 by The American Society of Hematology.