Association of CrkL with STAT5 in hematopoietic cells stimulated by granulocyte-macrophage colony-stimulating factor or erythropoietin.

CrkL is an adapter protein comprising Src homology (SH) 2 and SH3 domains. We investigated the molecule(s) associated with CrkL in factor-dependent cell lines. In the granulocyte-macrophage colony-stimulating factor (GM-CSF)-dependent cell lines TF-1 and UT-7, an approximately 95-kDa tyrosine-phosphorylated protein was precipitated along with CrkL after GM-CSF stimulation. The same protein was also observed when we used the erythropoietin (EPO)-dependent cell line UT-7/EPO, in an EPO stimulation-dependent manner. We identified it as STAT5 (signal transducer and activator of transcription 5, 96 kDa) by STAT5-specific antibodies. The direct binding of the SH2 domain of CrkL to STAT5 was demonstrated in far Western blotting and pull-down experiments using the glutathione S-transferase (GST) fusion construct CrkL-SH2. The addition of the oligopeptide containing phosphotyrosine 694 in STAT5A impaired the association between GST-CrkL-SH2 and STAT5. Furthermore, in a gel shift assay using prolactin-inducible element (PIE) as the probe, the DNA binding activity of STAT5 was inhibited by the interaction with GST-CrkL-SH2 in vitro. Finally, we found that STAT5 associated with CrkL did not bind to PIE sequence. These results suggest that CrkL participates in the Janus kinase (JAK)-STAT pathway by direct association with STAT5.