Cytokine signal transduction in P19 embryonal carcinoma cells: Regulation of Stat3-mediated transactivation occurs independently of p21ras-Erk signaling

Ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF) are members of a subfamily of related cytokines that share gp130 as common sig nal-transducing receptor component. CNTF has recently been demonstrated to induce increased survival and neuronal differentiation of P19 embryonal car cinoma (EC) cells; however, the molecular mechanisms underlying these effec ts are still elusive. Here we report that CNTF and LIF, but not interleukin -6, activated signal transducers and activators of transcription (STAT)repo rter constructs in P19 EC cells. Supershift analysis revealed that the STAT -element binding complex contained the transcription factor Stat3. Binding of Stat3 was inhibited by protein tyrosine kinase inhibitors, but not by th e broad serine/threonine protein kinase inhibitor, H7, However, H7 inhibite d CNTF-induced Stat3 transactivation, Using a dominant-negative p21ras cons truct and a specific inhibitor of mitogen-activated protein kinase kinase ( MEK; PD098059) we demonstrated that CNTF-induced Stat3 transactivation was independent of the p21ras-mitogen-activated protein kinase (MAPK) pathway, while CNTF-induced MAPK activation was p21ras- and MEK-dependent. Taken tog ether, our results demonstrate the activation of the p21ras-MAPK and STAT s ignal transduction pathways in response to CNTF and LIF in P19 EC cells and reveal that there is no modulating crosstalk between these pathways. Furth ermore, our data suggest that CNTF- and LIF-induced Stat3 activation in P19 EC cells involves an H7-sensitive p21ras/MAPK- and Ca2+-independent kinase , (C) 1999 Academic Press.