ERYTHROPOIETIN AND IL-3 INDUCE TYROSINE PHOSPHORYLATION OF CRKL AND ITS ASSOCIATION WITH SHC, SHP-2, AND CBL IN HEMATOPOIETIC-CELLS

The present study demonstrates that erythropoietin (Epo) and IL-3 indu ce tyrosine phosphorylation of the SH2/SH3-containing adapter protein CrkL and its transient association with tyrosine-phosphorylated SHP-2, Shc, and Cbl in a murine IL-3-dependent cell line, 32D, expressing th e Epo receptor (EpoR). In these cells, CrkL was constitutively complex ed with the guanine nucleotide exchange factor C3G, which was found to coimmunoprecipitate with Shc from Epo- or IL-3-stimulated cells. Stud ies using cells expressing mutant EpoRs showed that the Epo-induced ty rosine phosphorylation of CrkL is dependent on the membrane-proximal E poR cytoplasmic region involved in the activation of Jak2 as well as t he C-terminal 145 amino acid region which is required for tyrosine pho sphorylation of SHP-2 and Shc. It was further revealed that CrkL is re cruited to the tyrosin-phosphorylated EpoR, most likely through its in teraction with tyrosine-phosphorylated Shc and SHP-2. These results su ggest that CrkL is involved in the signaling pathways from the recepto rs for Epo and IL-3, most likely by modulating the activity of the Ras family GTPases through its interaction with C3G. (C) 1997 Academic Pr ess.