SHIP1, an SH2 domain containing polyinositol-5-phosphatase, regulates migration through two critical tyrosine residues and forms a novel signaling complex with DOK1 and CRKL

SHIP1 is an SH2 domain containing inositol-5-phosphatase that appears to be a negative regulator of hematopoiesis, The tyrosine kinase oncogene BCR/AB L drastically reduces expression of SHIP1. The major effect of re-expressin g SHIP1 in BCR/ABL-transformed cells is reduction of hypermotility, To inve stigate the potential signaling pathways involving SHIP1 in hematopoietic c ells, we overexpressed SHIP1 in a murine BCR/ABL-transformed Ba/F3 cell lin e and identified SHIP1-associated proteins. SHIP1 was found to form a novel signaling complex with BCR/ABL that includes DOK1 (p62(DOK)), phosphatidyl inositol 3-kinase (PI3K), and CRKL, each of which has been previously shown to regulate migration in diverse cell types. We found that DOK1 binds dire ctly through its PTB domain to SHIP1. Direct interaction of SHIP1 with CRKL was mediated through the CRKL-SH2 domain. Go-precipitation experiments sug gest that Tyr(917) and Tyr(1020) in SHIP1 are likely to mediate interaction s with DOK1, In contrast to wild type SHIP1, expression of tyrosine mutant SHIP1 by transient transfection did not alter migration. PI3K was likely li nked to this complex by CRKL, Thus, this complex may serve to generate a ve ry specific set of phosphoinositol products, possibly involved in regulatin g migration. Overall, these data suggest that proteins that interact with S HIP1 through Tyr(917) and Tr-1020, such as DOK1 and SHC, are likely to be i nvolved in the regulation of SHIP1 dependent migration.