Analysis of the Mechanism of Ultraviolet (UV) B Radiation – Induced Prostaglandin E2 Synthesis by Human Epidermoid Carcinoma Cells

Stimulation of cultured human keratinocytes with interleukin (IL)-1α is known to elicit prostaglandin (PG) E2 release. Ultraviolet (UV) B radiation induces keratinocyte PGE2 and cytokine production. The present study deals with the autocrine roles of UVB-induced, keratinocyte-derived cytokines IL-1 and tumor-necrosis-factor (TNF) α and their corresponding receptor molecules for UVB-induced PGE2 release. In vitro exposure of transformed human keratinocytes (KB cells) induced PGE2 production five- to eightfold. This increase was inhibited by 70%, if irradiated cells were cultured in presence of monoclonal antibody (MoAb) M4, which blocks IL-1 effects by binding to the type 1 IL-1 receptor (IL-1R). In contrast, MoAb M22, which blocks the type 2 IL-1R, had no significant effects. Addition of recombinant human TNFα to unirradiated KB cells resulted in five- to eightfold increased PGE2 synthesis, and this increase could be mimicked by stimulation of KB cells with MoAb htr-9, which exerts TNFα-like bioactivity by binding to the 55-kD TNF receptor (TNFR). UVB-induced PGE2 synthesis was blocked by 50% in the presence of neutralizing anti-TNFα-Ab, and was completely inhibited by addition of both anti- TNFα-Ab and MoAb M4. To elucidate a possible regulatory intracellular step in PGE2 synthesis, specific cyclooxygenase activity in KB cells was determined. Following UVB treatment, cyclooxygenase activity increased twofold, but remained unaltered, if irradiated KB cells were cultured in the presence of anti-TNFα-Ab plus MoAb M4. These studies indicate that keratinocyte-derived TNFα and IL-1 together mediate UVB-induced PGE2 release via specific cell surface receptors, and that one intracellular mechanism is an increased prostanoid-synthesizing capacity of irradiated cells