The inositol 5-phosphatase SHIP is expressed as 145 and 135 kDa proteins in blood and bone marrow cells in vivo, whereas carboxyl-truncated forms of SHIP are generated by proteolytic cleavage in vitro

Abstract

The inositol polyphosphate 5-phosphatase SHIP plays an important role in negative signalling in B cells and mast cells and in the down-regulation of cytokine receptor-mediated signals in myeloid cells. SHIP is expressed as a 145 kDa full-length protein and an isoform of 135 kDa due to alternative splicing. Additional smaller forms of SHIP which are truncated at the carboxy terminus have been described in bone marrow and peripheral blood mononuclear cells (PBMC). Our data demonstrate that human bone marrow cells and PBMC from healthy donors and patients with acute myeloid leukemia express the 145 kDa form of SHIP and low amounts of a 135 kDa form of SHIP in vivo whereas C-terminal-truncated SHIP proteins are generated by a PMSF-sensitive protease during the preparation of cell lysates in vitro. We have further characterized this protease and identified a proteolytic cleavage site in the human SHIP protein C-terminal to tryptophan residue 941. These data support a physiological role for the 145 and 135 kDa forms of SHIP in bone marrow and peripheral blood cells from normal donors and patients with acute myeloid leukemia.

PSTPIP2, a Protein Associated with Autoinflammatory Disease, Interacts with Inhibitory Enzymes SHIP1 and Csk

“…8). The 100-kDa form of SHIP1 prevailing in these immunoprecipitates is likely the result of proteolytic cleavage and has been described previously (42). These results confirm that PSTPIP2 is also expressed in human granulocytes and that it participates in similar interactions as its murine counterpart.…”

Restoration of SHIP activity in a human leukemia cell line downregulates constitutively activated phosphatidylinositol 3-kinase/Akt/GSK-3β signaling and leads to an increased transit time through the G1 phase of the cell cycle

“…Proteolytic cleavage of SHIP in hematopoietic cell lines and in primary leukemia samples can occur during the preparation of protein extracts under nondenaturing conditions resulting in an artificial cleavage of SHIP proteins. 19 The analysis of SHIP proteins in Jurkat cell extracts prepared under denaturing conditions, that is, in boiling SDS buffer, which avoids any artificial cleavage of SHIP, confirmed the absence of SHIP proteins in Jurkat cells (data not shown).…”

“…15,16 SHIP is expressed in all hematopoietic cells analyzed so far, including CD34 þ cells derived from human bone marrow. [17][18][19] Stimulation of mast cells derived from SHIP À/À mice with granulocytemacrophage colony stimulating factor (GM-CSF) or interleukin-3 (IL-3) results in an increased and prolonged PI3K-dependent PtdIns(3,4,5)P 3 accumulation and Akt activation in these cells. 20 In addition, targeted disruption of SHIP in mice leads to a myeloproliferative disorder due to an increased sensitivity of the hematopoietic cells for several cytokines including GM-CSF and IL-3.…”

Dual-specificity phosphatase Pyst2-L is constitutively highly expressed in myeloid leukemia and other malignant cells

“…Phosphatases may downregulate biological processes by dephosphorylating inducer molecules or enhance such processes by removing an inhibitory phosphate from kinases (Biethahn et al, 1999). Phosphatases such as PP1, PP2A, PP2B, PP2C (Yamamoto et al, 1999;Ofek et al, 2003), PTPN6 (Beghini et al, 2000), PTP epsilon C (Tanuma et al, 2000;Andersen et al, 2001), SHIP (Wagers et al, 1998) and SHP-1 (Horn et al, 2001) were found to be highly expressed in human malignant cells as compared to the corresponding nonmalignant counterparts. In some cases, these enzymes seem to be involved in tumorigenesis and in tumor progression (Parsons, 1998;Gopalakrishna et al, 1999;Yamamoto et al, 1999;Hwang et al, 2001;Poetsch et al, 2001).…”