Cytokine-inducible SH2 protein (CIS3) and JAK2 binding protein (JAB) abolish prolactin receptor-mediated STAT5 signaling

The ability of five members of the cytokine-inducible SH2 protein family (C IS1-4) and JAK2 binding (JAB) protein to affect prolactin receptor (PRLR)-m ediated activity was tested in human 293 embryonic kidney fibroblasts trans iently transfected with rat PRLR, five concentrations of CIS/JAB Myc-tagged cDNAs and a STAT5-responsive reporter gene encoding luciferase, The protei n expressions of CIS1, CIS2, CIS3 and JAB were comparable, whereas the leve l of CIS4 was slightly lon er. PRLR-mediated luciferase activity was abolis hed in a dose-dependent manner in cells transfected with cDNA of CIS3 or JA B, even at concentrations below the level of protein detection by anti-Myc antibody, In contrast, CIS1, CIS2 and CIS4 had little or no effect, despite similar levels of expression, CIS1 expression in postpartum mouse mammary glands was high and changed little in the course of 3 days, CIS2 and CIS3 e xpression was also high and increased further, whereas JAB expression was v ery low. These results hint that at least in mammary gland CIS3 is likely t he main physiological negative regulator of the PRLR-mediated JAK2/STAT5 pa thway. (C) 1998 Federation of European Biochemical Societies.