The Csk-like proteins Lsk, Hyl, and Matk represent the same Csk homologous kinase (Chk) and are regulated by stem cell factor in the megakaryoblastic cell line MO7e

Recently, the cDNAs for Lsk, Matk and Hyl, three Csk-related protein tyrosine kinases, have been cloned. We have examined the relationship of Lsk, Matk and Hyl, and found that the gene for each of these proteins is localized to the same region of human chromosome 19. Further, the proteins encoded by Lsk and Matk cDNAs are immunologically similar. These data strongly suggest that Lsk, Hyl and Matk are the same gene product. Previous reports demonstrating expression of Hyl and Matk in hematopoietic lineages led us to investigate the regulation of Lsk expression in response to stem cell factor (SCF) and granulocyte-macrophage colony stimulating factor (GM-CSF) in M07e, a human leukemic cell line. Induction of Lsk/Hyl/Matk protein and mRNA was observed after treatment with SCF but not with GM-CSF. GM-CSF and IL-3, potent mitogens, had no effect on Lsk/Hyl/Matk expression. In contrast, PMA induced Lsk/HyYMatk but did not stimulate proliferation. Therefore, induction of Lsk/ Hyl/Matk does not correlate with the capacity to stimulate proliferation. None of the stimuli examined increased Csk protein or mRNA expression. These data demonstrate differential regulation of Csk family members by cytokines and suggest a role for Lsk/ Hyl/Matk in responses mediated by SCF and PMA. Further, our data demonstrate that, as has been seen in blood monocytes, cytokine driven translational control of Lsk/Hyl/ Matk is likely a critical mode of regulation. Lastly, since our studies strongly suggest that the Lsk, Hyl and Matk kinases are related and regulated distinctly from Csk, we and several of the original authors have agreed to rename this kinase the Csk homologous kinase (Chk).