Oncostatin M (OSM) is an IL-6/LIF cytokine family member whose role has been identified in a range of biological activities in vitro, including upregulation of inflammatory gene expression and regulation of connective tissue metabolism. Previously, we identified murine OSM (mOSM) as an inducer of the eosinophil-chemoattractant protein eotaxin-1, both in vitro using fibroblast cell lines and in vivo from mouse lung tissues. Using the NIH 3T3 cell line, we demonstrate the requirement of PI3'K activation for mOSM induction of eotaxin-1 through inhibition of both mOSM-stimulated mRNA and protein expression using the PI3'K antagonist LY294002. By assessment of phosphorylation of the downstream mediator Akt, we show mOSM to be differentially capable of activating PI3'K relative to the related gp130-utilizing cytokine IL-6. Assessment of eotaxin-1 gene expression utilizing PKB/Akt mutant-transfected NIH 3T3 cell lines demonstrated Akt is not involved in upstream regulation of eotaxin-1 through mOSM, indicating an alternate kinase pathway downstream of PI3'K may be involved. We demonstrate that mOSM stimulation of expression of eotaxin-1 is reduced by PD98059, a MAPK kinase inhibitor selective for MEK1. Both LY294002 and PD98059 attenuated mOSM-induced phosphorylation of ERK1/2 MAP kinase and also reduced binding of an AP-1 responsive promoter element, a transcriptional complex known to be MAPK-sensitive. Further, LY294002 pretreatment reduced mOSM-stimulated expression of the downstream AP-1 co-factor JunB, while PD98059 reduced levels of JunB as well as c-Fos. These results provide evidence for a previously unidentified signaling mechanism utilized by mOSM for the induction of eotaxin-1.