ULTRAVIOLET-RADIATION STIMULATES A BIPHASIC PATTERN OF 1,2-DIACYLGLYCEROL FORMATION IN CULTURED HUMAN MELANOCYTES AND KERATINOCYTES BY ACTIVATION OF PHOSPHOLIPASE-C AND PHOSPHOLIPASE-D

Ultraviolet radiation (UVR) induces melanin synthesis by human epidermal melanocytes, and phospholipid-derived 1,2-diacylglycerols (DAGs) have been implicated in mediating this response. In previous experiments, addition of the synthetic DAG 1-oleoyl-2-acetylglycerol to cultured pigment cells stimulated melanogenesis. The purpose of the present study was to analyse the effects of UVR on the endogenous generation of DAGs. It was found that in a number of cultured cell types, including human melanocytes and B16 mouse melanoma cells, but also human keratinocytes and Swiss 3T3 fibroblasts, exposure to a single dose of UVR stimulated a biphasic increase in endogenous DAG formation. An early transient rise, over seconds, was followed by a more sustained delayed rise over minutes. The early rise in DAG levels was accompanied by a transient rise in inositol trisphosphate formation, indicating activation of phosphatidylinositol-specific phospholipase C. The delayed rise was accompanied by activation of phospholipase D. This endogenous DAG formation by pigment cells is further evidence for the involvement of DAGs in UVR-induced epidermal melanin synthesis. Since DAG formation is also seen in other cells types, it is possible that DAGs may be involved in an array of UVR-induced responses.