Increased synthesis of high-molecular-weight cPLA(2) mediates early UV-induced PGE(2) in human skin

Ultraviolet light (UV) B-induced inflammation is characterized by dramatic increases in prostaglandin E(2) (PGE(2)) synthesis due to enhanced arachidonate deacylation from the membrane. Therefore, the effect of UV on synthesis, mass, and distribution of the high-molecular-weight phospholipase A(2) (cPLA(2)) in cultured human keratinocytes and human skin was studied. The 105-kDa cPLA(2) was demonstrated to be the critical enzyme in UV-induced PGE(2) synthesis and erythema in the first 6 h postirradiation. Immunoprecipitation of S-35-labeled protein showed cPLA(2) synthesis increased three- to fourfold 6 h after irradiation. Immunoprecipitated P-32-labeled cPLA(2) demonstrated phosphorylation of cPLA(2) was concurrently induced, suggesting that UV also activates cPLA(2). This increase in cPLA(2) synthesis and activation also closely correlated with increased PGE(2) synthesis and [H-3]arachidonic acid release and was effectively blocked by both an S-oligonucleotide antisense to cPLA(2) and methyl arachidonate fluorophosphate, a specific inhibitor of cPLA(2). Biopsy and histochemical examination of irradiated sites from human volunteers revealed that only erythematous sites expressed increased amounts of cPLA(2), whereas nonerythematous irradiated sites did not. In contrast, cyclooxygenase-1 and -2 in cultures and skin explants were unaffected 6 h post-UV, and no change in cyclooxygenase activity was observed at this time. These results suggest that increased cPLA(2) synthesis occurs only when skin is exposed to UV doses that are sufficient to cause erythema and indicate expression of cPLA(2) participates in acute UV inflammation.