In addition to the IKK kinase activation, LPS-induced IRAK-1 activation triggers cascades of intracellular signaling events including the MAPK such as the ERK, the JNK, and the p38 kinase (27). In this study, we determined the effect of acute and chronic alcohol exposure on activation of MAPKs: ERK, JNK, and p38. Using Western blotting and phospho-specific MAPK Abs we observed that acute alcohol exposure decreased LPS-induced phospho-ERK kinase levels whereas chronic alcohol exposure significantly increased LPS-induced phospho-ERK kinase activity without any change in total ERK levels (Fig. 5, A and B). Furthermore, a minimal increase in LPS-induced phospho-p38 MAPK was noted in monocytes exposed to acute alcohol whereas chronic alcohol exposure did not have any effect on LPS-induced phospho-p38 MAPK (Fig. 5A). The JNK MAPK was not significantly affected by alcohol exposure in human monocytes. Importantly, inhibition of the ERK MAPK, using a specific inhibitor PD98059, in chronic alcohol exposed monocytes resulted in inhibition of chronic alcohol induced increase in LPS-induced TNF-α production (Fig. 5C) indicating an important role for ERK MAPK in inflammatory cytokine production after chronic alcohol exposure in human monocytes.
