CLONING AND CHARACTERIZATION OF NOVEL CIS FAMILY GENES

We have reported two JAK-signaling modulators, CIS (cytokine-inducible SH2 protein) and JAB (JAK2 binding protein), which are structurally r elated. Here we cloned three additional CIS family genes (CIS2, CIS3, and CIS4) on the basis of an expression sequence tag (EST) database se arch. We also found at least two additional candidates of this gene fa mily in the database. These genes were induced by erythropoietin and g ranulocyte-macrophage colony stimulating factor in certain hematopoiet ic cell lines. The SH2 domain and a C-terminal 40 amino acid region, d esignated the CIS homology domain (CH domain), are highly conserved in this family, while the N-terminal regions of these proteins share lit tle similarity. A yeast two hybrid assay and in vitro and in vivo bind ing assays revealed that in addition to JAB, CIS3 bound to the JAK2 ty rosine kinase domain (JH1), although the interaction of CIS3 with the JAK2-JH1 domain was much weaker than that of JAB. Transient expression of JAB and CIS3, but not other CISs, strongly inhibited leukemia inhi bitory factor (LIF)-induced STAT3-reporter gene activation in 293 cell s. Furthermore, constitutive overexpression of JAB and CIS3 in M1 leuk emia cells prevented LIF-induced differentiation and growth arrest. Al though the physiological function remains to be investigated, CIS fami ly genes could play a role in the negative regulation of cytokine sign aling by interacting with specific targets. (C) 1997 Academic Press.