The involvement of PI3-K/Akt-dependent up-regulation of Mcl-1 in the prevention of apoptosis of Hep3B cells by interlenkin-6

Interleukin-6 (IL-6) is a pleitrophic cytokine that not only regulates grow th and differentiation of many cell types, but also induces production of a cute phase proteins (A4P) in hepatocytes. Our previous works have demonstra ted that both PI 3-K/Akt and STAT3 pathways mere concomitantly activated an d cooperatively mediated the anti-apoptotic effect of IL-6. This investigat ion reports that IL-6 protected cells against apoptosis induced by a variet y of agents including, TGF-beta, Uv and retinoic acid (RA) in Hep3B cells, suggesting that IL-6 is a fundamental determinant of hepatic cell survival. Mel-1, but not other Bcl-2 family members, was rapidly up-regulated by IL- 6, with a peak (approximately 3-4-fold) appearing at 4 h. Transient transfe ction of cells with a mcl-1 antisense vector, resulting in a 50-60% reducti on of the anti-apoptotic effect of IL-6, indicating that Mcl-1 is a downstr eam effector of IL-6. Which signaling pathway transduced by IL-6 responsibl e for the Mcl-1 up-regulation was further investigated. In Hep3B cells, the JAK/STAT3, ERR, and PI 3-K/Abt pathways mere activated by IL-6 stimulation . Blocking JAK/STAT3 activation with a dominant-negative mutant STAT3F or a JAK inhibitor AG490 could not influence IL-6-mediated Mcl-1 up-regulation. Similarly, PD98059 treatment, a MEK specific inhibitor, also failed to inh ibit Mcl-1 expression. However, the IL-6-induced Mcl-1 upregulation was eff ectively attenuated in the presence of PI 3-K inhibitors, LY294002 and wort mannin. Expression of dominant-negative Akt, but not Etk, could abrogate th e IL-6-induced increase of Mcl-1. In conclusion, our results suggest that t he anti-apoptotic effect of IL-6 is mediated, at least in part, bai Mcl-1 e xpression and that is mainly through the PI 3-K/Akt-dependent pathway.