Characterization of the substrate specificity of the inositol 5-phosphatase SHIP1

SHIP1 is an inositol 5-phosphatase which is well established for its tumour suppressor potential in leukaemia. Enzymatically, two SHIP1 substrates, PtdIns(3,4,5)P₃ and Ins(1,3,4,5)P₄ have been identified to date. Additional substrates were found for the homologue SHIP2. In this study, we identified new inositol phosphate (InsP) substrates of SHIP1 by metal dye detection high-performance liquid chromatography and compared the substrate profiles of SHIP1 and SHIP2. We were able to verify Ins(1,3,4,5)P₄ as a substrate of SHIP1 and interestingly found Ins(1,2,3,4,5)P₅ and Ins(2,3,4,5)P₄ to be preferably used as substrates and Ins(1,4,5,6)P₄ and Ins(2,4,5,6)P₄ to be weak substrates. All of those except Ins(2,3,4,5)P₄ are also known substrates of SHIP2 indicating a possible exclusive role of Ins(2,3,4,5)P₄ hydrolysis for SHIP1 but not SHIP2 function.