Ultraviolet (UV) irradiation is a major environmental factor responsible for a high incidence of premature skin aging, referred to as photoaging, as well as skin cancer and melanoma. UVA irradiation represents 90% of the solar UV light reaching the earth's surface, and yet the mechanisms by which it exerts its biological effects are not clear. UVA penetrates into the skin tissue, reaching the basal layers of the active dividing cells and, therefore, the contribution of UVA to skin damage may be significant. The majority of UVA energy is absorbed by unidentified photosensitizers in the cells which are postulated to generate reactive oxygen species (ROS). It has been believed that both chronological aging and photoaging share the same molecular features and, as such, it is very common to utilize UV irradiation for induction of skin aging. To determine the involvement of protein kinase isoforms in chronological aging and photoaging, we utilized in vitro aging model systems of primary murine fibroblasts and primary fibroblasts isolated from PKC null mice. We show for the first time distinct involvement of PKC isoforms PKCdelta and PKCalpha in photoaging versus cellular senescence. While chronological aging is accompanied by overexpression and activation of PKCalpha, UV irradiation and ROS production are associated with photoaging accompanied by PKCdelta downregulation and nuclear translocation.
(c) 2008 Wiley-Liss, Inc.