EXPRESSION OF CYCLOOXYGENASE IN THE EPIDERM™ HUMAN SKIN MODEL: REGULATION BY ULTRAVIOLET RADIATION AND CYTOKINES.

Cyclooxygenase-2 (COX-2) appears to play an important role in skin carcinogenesis caused by solar ultraviolet radiation (UVR): UVR induces COX-2 expression in human skin, COX-2 activity is upregulated in skin cancers and COX inhibitors reduce UVR-induced tumor formation. In this report, we use RT-PCR, Western blotting and ELISA to study the effect of UVR on COX message, protein and metabolites, respectively, in the EpiDerm in vitro human skin equivalent. There are two isoforms of COX, COX-1 (constitutive) and COX-2 (inducible). COX enzymes metabolize arachadonic acid (AA) to eicosanoid products including prostaglandin E2 (PGE-2) thromboxane A2 and PGI-2, which are thought to contribute to skin carcinogenesis. COX may also metabolize AA to 8-isoprostane (8IP), a novel mitogenic prostaglandin previously thought to be formed only via free radical pathways. EpiDerm tissues expressed COX-1 message and protein constitutively, and secreted PGE-2 and 8IP into the culture medium. COX-2 message and protein were also detectable. UVR enhanced COX-2 expression without effecting COX-1, and increased production of both PGE2 and 8IP. COX inhibitors reduced production of PGE2 and 8IP to below baseline levels, indicating a metabolic rather than free radical mechanism of formation. Additional experiments were conducted to study regulation of COX expression by cytokines in the absence of UVR. IL-1α, IL-1β or TNFα induced expression of COX-2 without effect on COX-1, and in-creased production of PGE-2 and 8IP. Combinations of IL-1α or IL-1β with TNFα produced additive PGE-2 and 8IP production. Thus, EpiDerm tissues behave similarly to in vivo human skin with respect to regulation of COX-2 by solar UVR and cytokines. COX-dependent production of 8IP by human skin equivalents is demonstrated for the first time, suggesting a potential role for this mitogenic metabolite in skin carcinogenesis. Finally, the results indicate that in vitro human skin equivalents are useful models for study of COX regulation by UVR, and related aspects of human skin carcinogenesis.

8-IP, AA, Arachidonic acid, COX-2, Carcinogenesis, Cyclooxygenase, Cytokines, Eicosanoid, EpiDerm, Gene expression, IL-1a, Inflammation, PGE-2, PGI-2, Prostaglandin E-2, Skin, UVR, Ultraviolet