Interleukin-6 (IL-6) has been identified as an important growth regulator of lung cancer cells. Elevation of serum levels of IL-6 has been found in a subpopulation of lung cancer patients, but rarely in patients with benign lung diseases. Approximately 15 % of non-small cell lung cancer (NSCLC) tumors exhibit neuroendocrine (NE) properties (NSCLC-NE) and have been suggested to have the biological characteristics similar to small cell lung cancer (SCLC) with early metastasis and initial responsiveness to chemotherapy. We recently showed that IL-6 promotes cell proliferation and downregulates the expression of neuron-specific enolase (NSE, one of the major NE markers) in NSCLC-NE cells. In this study, we show that IL-6 stimulates a transient increase of tyrosine phosphorylation of STAT3 in a dose-dependent fashion. Inhibition of STAT3 signaling pathway by either AG-490 (JAK2-specific inhibitor) or overexpression of STAT3Y705F (a dominant-negative STAT3) reverses NSE expression in IL-6treated NSCLC-NE cells. In addition, IL- 6 induces phosphorylation and activation of p38 MAPK. SB-203580, a p38 MAPK- specific inhibitor, inhibits IL-6-induced p38 MAPK phosphorylating activity and suppresses IL-6-stimulated cell proliferation. Together, our results indicate that STAT3 signaling pathway is involved in IL-6-induced NE differentiation and that p38 MAPK is associated with IL-6-stimulated growth regulation in NSCLC-NE cells. These data suggest that both kinase pathways play critical roles in the pathogenesis of NSCLC-NE malignancies, providing new molecular targets for future therapeutic approaches.
