CIS, A CYTOKINE INDUCIBLE SH2 PROTEIN, IS A TARGET OF THE JAK-STAT5 PATHWAY AND MODULATES STAT5 ACTIVATION

We searched for immediate early cytokine responsive genes and isolated a novel gene, CIS (Cytokine Inducible SH2 containing protein) that is induced in hematopoietic cells by a subset of cytokines including int erleukin-2 (IL-2), IL-3, and erythropoietin (EPO), The mutant IL-2 rec eptor that fails to activate STAT5 could not induce CIS, suggesting th at STAT5 is involved in the cytokine-inducible expression of CIS. We c loned the 5'-fllanking region of the CIS gene and found that about 200 bases upstream of the transcription-initiation site contain four pote ntial STAT5 binding sites (MGF boxes). Luciferase reporter assays show ed that these MGF boxes were essential for EPO-dependent promoter acti vity. Expression of STAT5 and the EPO receptor in HEK293 cells conferr ed EPO-dependent activation of the CIS promoter. These data indicate t hat CIS is-a target of the JAK-STAT5 pathway of cytokine receptors. CI S contains an SH2 domain and binds to tyrosine-phosphorylated EPO and IL-3 receptors. In HEK293 cells expressing STAT5 and the EPO receptor, EPO-dependent tyrosine phosphorylation of STAT5, as well as EPO-depen dent CIS-promoter activation, was suppressed when CIS was coexpressed. Moreover, the induction of oncostatin M-r another STAT5 target, as we ll as the tyrosine-phosphorylation of STAT5, were Partially suppressed by CIS expression in Ba/F3 cells. Thus, CIS is a feedback modulator o f STAT5; its expression is induced by STAT5 and it negatively modulate s STAT5 activation. (C) 1997 by The American Society of Hematology.