Induction of C-X-C chemokines, growth-related oncogene alpha expression, and epithelial cell-derived neutrophil-activating protein-78 by ML-1 (interleukin-17F) involves activation of Raf1-mitogen-activated protein kinase kinase-extracellular signal-regulated kinase 1/2 pathway.

Neutrophil recruitment into the airway typifies pulmonary inflammation and is regulated through chemokine network, in which two C-X-C chemokines play a critical role. Airway epithelial cells and vein endothelial cells are major cell sources of chemokines. ML-1 (interleukin-17F) is a recently discovered cytokine and its function still remains elusive. In this report, we investigated the functional effect of ML-1 in the expression of growth-related oncogene (GRO)alpha and epithelial cell-derived neutrophil activating protein (ENA)-78. The results showed first that ML-1 induces, in time- and dose-dependent manners, the gene and protein expressions for both chemokines in normal human bronchial epithelial cells and human umbilical vein endothelial cells. Furthermore, selective mitogen-activated protein kinase kinase (MEK) inhibitors 2'-amino-3'-methoxyflavone (PD98059), 1,4-diamino-2,3-dicyano-1,4-bis(o-aminophenylmercapto) butadiene (U0126), and Raf1 kinase inhibitor I partially inhibited Ml-1-induced GROalpha and ENA-78 production. In contrast, the combination of PD98059 and Raf1 kinase inhibitor I completely abrogated the chemokine production, whereas a protein kinase C inhibitor, 2-(1-(3-aminopropyl) indol-3-yl)-3-(1-methylindol-3-yl) maleimide, acetate (Ro-31-7549), and a phosphatidylinositol 3-kinase inhibitor, 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002), did not affect their production. Together, these data indicates a role for Raf1-MEK-extracellular signal-regulated kinase 1/2 pathway in ML-1 induced C-X-C chemokine expression, suggesting potential pharmacological targets for modulation.