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The Effects of UV Irradiation
a Laboratoire de Biologie et Biochimie Cellulaire du Vieillissement, EA 3106/IFR 117, Université Paris 7-Denis Diderot, 75251 Paris Cedex 05, France b LVMH Branche Parfums et Cosmétiques, Laboratoires Recherche et Développement, 45804 Saint Jean de Braye Cedex, France
Key Words: proteasome • aging • photoaging • UV irradiation
Address for correspondence: Bertrand Friguet, Laboratoire de Biologie et Biochimie Cellulaire du Vieillissement, Université Paris 7-Denis Diderot, 2 Place Jussieu, 75251, Paris Cedex 05, France. Voice/fax: 33-1-44-27-82-34. bfriguet{at}paris7.jussieu.fr
Cellular aging is characterized by the accumulation of oxidatively modified proteins that result, at least in part, from impaired degradation of abnormal proteins. The proteasome is the major intracellular proteolytic system implicated in the removal of abnormal and oxidized proteins. In human epidermal cells, previous studies have evidenced that proteasome function is decreased during aging as well as upon UV irradiation, which is the main component of photoaging. The age-related decline of proteasome activity has been reported to be due to either or both decreased proteasome subunits expression and content, inactivation upon alteration of proteasome subunits, and accumulation of endogenous inhibitors, such as highly oxidized and cross-linked proteins. To gain further insight in the mechanisms that might be implicated in the decreased activity of the proteasome upon photoaging, purified 20S human proteasome has been exposed to UVA- and UVB-irradiation. The effect of such an irradiation on proteasome peptidase activities has been monitored and shown to promote a stimulation or an inhibition of the peptidase activities depending on whether the proteasome is under its latent or a nonphysiological active form. Analysis of the patterns of proteasome subunits by 2D gel electrophoresis has revealed modification for several subunits for UV-irradiated proteasome only in its irreversibly activated form, compared with nonirradiated and irradiated latent forms, indicating that the 20S proteasome is rather resistant to UV irradiation.
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