Differential contributions of Akt, Src and ERK signaling in regulating MUC4 expression. (A) ChIP assay conducted on CD18 cells stimulated with nicotine, IFN-γ or RA in the presence of chemical inhibitors of LY294002, PD98059 and PP2 showed ERK and Src-family kinases may be involved in the upregulation of MUC4 upon nicotine stimulation. At the same time, in the case of IFN-γ LY294002, PD98059 and PP2 showed significant decreased expression of MUC4, whereas with RA stimulation LY294002 and PD98059 showed decreased expression of MUC4 but PP2 did not show significant inhibition in the expression of MUC4. (B) Real time-PCR supported the ChIP assay results where ERK and Src-family kinases were involved in the upregulation of MUC4 upon nicotine stimulation. In the case of IFN-γ, PI3K, MEK and Src family kinases are involved in the expression of MUC4, whereas with RA stimulation PI3K and MEK kinases are involved in the expression but Src-family kinases had a lesser role. (C) Real time-PCR showing combination of nicotine and IFN-γ involves ERK as well as Src in the induction of the MUC4 promoter whereas (D) Src seemed to have only a minimal effect when RA was combined with nicotine (*p ≤ 0.01, **p ≤ 0.03).