Atmospheric ozone layer loss has recently focused attention on the destructive effects of environmental UV light exposure in humans. UV light injury produces oxygen radical formation causing skin inflammation acutely. Recent work in our laboratory suggests that cytosolic phospholipase A2 (cPLA2) is an active participant in this process. cPLA2 is a recently described high molecular weight phospholipase. It has lysophospholipase activity and is linked to prostaglandin formation. It is 4 times larger than other phospholipases, suggesting it serves additional functions in the cell. However, little information on its biological role is known. Recent work in our lab shows cPLA2 is highly induced by UV irradiation and by oxidative stimuli, and is responsible for both increased PGE2 and PGE1 synthesis. While the capacity of cPLA2 to hydrolyze arachidonic acid is well described, its capacity to hydrolyze dihomo-gamma-linolenic acid (DHGLA) necessary for PGE1 synthesis has not been reported. These activities suggest that while cPLA2 contributes to UV-induced PG synthesis, it may also play a role in membrane remodeling after UV exposure. The high levels of cPLA2 expression produced by irradiated epidermis and the capacity of cPLA2 to mediate PGE1 formation suggest that study of cPLA2 in this model system will enhance knowledge about both the biological functions of cPLA2 and improve our understanding of UV injury. Using anti-cPLA2 antibody, the fluorophosphonate inhibitor of cPLA2, as well as antisense and transfection strategies, the studies described in this proposal will investigate the effects of UV exposure on signalling leading to CPLA2 synthesis and phosphorylation, document the role of cPLA2 in UV-stimulated fatty acid release. The understanding of cPLA/2 regulation and function provided by these studies will provide a backdrop for defining whether epidermis can modify its fatty acid composition in response to UV-induced oxidative stress, and whether cPLA2- mediated eicosanoid product formation can modify the viability and proliferation of irradiated cells.
Two specific aims are proposed. In the first aim, the mechanisms which regulate cPLA/2 expression and activity in epidermis will be detailed. These experiments are designed to define the key signalling pathways initiating changes in cPLA2 synthesis and phosphorylation. These studies will also define how cPLA2 participates in the formation of PGE1, by measuring its capacity to hydrolyze DHGLA-containing phospholipids and determine whether PGE1 formation is influenced by irradiation or oxidative stress.
In specific Aim B, the functional consequences of increased cPLA2 expression will be examined. Using selective inhibitors, expression and antisense strategies, these experiments will dissect the effects of increased cPLA2-mediated fatty acid release to show i) if expression of cPLA2 contributes to clinical inflammation occurring after UV exposure, ii) determine if cPLA/2 facilitates fatty acid recovery after irradiation, and iii) document its role in UV-induced epidermal cell death. Knowledge of the role of cPLA2 in UV injury will greatly increase our understanding of the biology of cPLA2 as well as the mechanisms protecting the epidermis from environmental UV and other oxidative injuries.
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