Involvement of ERK AND p38 MAP kinase in AAPH-induced COX-2 expression in HaCaT cells

Cyclooxygenase-2 (COX-2) appears to play an important role in inflammation and carcinogenesis, and 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) is a hydrophilic azo compound known to generate free radicals. Because reactive oxygen species (ROS) are known to elevate COX-2 expression, we evaluated the effect of AAPH on the expression of COX-2 in a human keratinocyte cell line, HaCaT. When cells were exposed to AAPH, marked COX-2 induction was observed. To clarify the signaling mechanism involved, we next investigated the effects of AAPH upon three major subfamilies of the mitogen-activated protein kinases (MAPKs). AAPH caused an increase in the phosphorylation of extracellular signal-regulated kinase (ERK), p38 and c-Jun NH(2)-terminal kinase (JNK). Furthermore, we found that PD98059, an ERK pathway inhibitor, and SB203580, a p38 MAPK inhibitor, diminished AAPH-induced COX-2 expression and PGE(2) production, whereas JNK inhibitor did not suppress COX-2 expression or PGE(2) production by AAPH. These findings suggest that the ERK and p38 MAPK pathways, but not the JNK pathway, are involved in AAPH-induced inflammatory progression. In addition, we found that both the water-soluble Vitamin E derivative, Trolox, and the green tea constituent, (-)-epigallocatechin gallate (EGCG), diminished AAPH-induced COX-2 expression and p38 activation.