The two SH2-domain-containing inositol 5-phosphatases SHIP1 and SHIP2 are coexpressed in human T lymphocytes

The activation of many hematopoietic cells via cytokine receptors, as well as B and T cell receptors, leads to the tyrosine phosphorylation of Shc and its association with both Grb2-Sos1 complexes and with a 145 kDa protein r eferred to as the SH2 containing inositol 5-phosphatase (SHIP1). In a searc h of putative 5-phosphatase isoenzymes, we have isolated a second SH2 domai n containing inositol 5-phosphatase, referred to as (SHIP2). Both SHIP1 and SHIPS are coexpressed in human T lymphocytes. This was shown at the protei n level by Western blot analysis in transformed T cell lines and in periphe ral blood T lymphocytes either unstimulated or after in vitro activation th rough TCR-CD3 complex. SHIP1 protein level was not modulated after activati on of T lymphocytes, in contrast to SHIP2, which was increased after longte rm stimulation. SHIP1 was tyrosine phosphorylated in resting naive T cells. This was not observed in the transformed T cell lines. T lymphocyte is the refore a model of coexpression of the two SHP-containing inositol 5-phospha tases SHIP1 and SHIP2.