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J. Biol. Chem., Vol. 280, Issue 52, 43257-43263, December 30, 2005

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RhoB Protects Human Keratinocytes from UVB-induced Apoptosis through Epidermal Growth Factor Receptor Signaling^*

Bruno Canguilhem, Anne Pradines, Caroline Baudouin, Céline Boby, Isabelle Lajoie-Mazenc, Marie Charveron, and Gilles Favre1

From the INSERM U563, Département Innovation Thérapeutique et Oncologie Moléculaire, Institut Claudius Regaud, Université Paul Sabatier, 20/24 rue du Pont Saint-Pierre, 31052 Toulouse Cedex France and the Institut de Recherche Pierre Fabre, Laboratoire de Biologie Cellulaire, 2 rue Viguerie, BP3071, 31025 Toulouse Cedex 3, France

Exposure of the skin to UVB light results in the formation of DNA photolesions that can give rise to cell death, mutations, and the onset of carcinogenic events. Specific proteins are activated by UVB and then trigger signal transduction pathways that lead to cellular responses. An alteration of these signaling molecules is thought to be a fundamental event in tumor promotion by UVB irradiation. RhoB, encoding a small GTPase has been identified as a DNA damage-inducible gene. RhoB is involved in epidermal growth factor (EGF) receptor trafficking, cytoskeletal organization, cell transformation, and survival. We have analyzed the regulation of RhoB and elucidated its role in the cellular response of HaCaT keratinocytes to relevant environmental UVB irradiation. We report here that the activated GTP-bound form of RhoB is increased rapidly within 5 min of exposure to UVB, and then RhoB protein levels increased concomitantly with EGF receptor (EGFR) activation. Inhibition of UVB-induced EGFR activation prevents RhoB protein expression and AKT phosphorylation but not the early activation of RhoB. Blocking UVB-induced RhoB expression with specific small interfering RNAs inhibits AKT and glycogen synthase kinase-3 phosphorylation through inhibition of EGFR expression. Moreover, down-regulation of RhoB potentiates UVB-induced cell apoptosis. In contrast, RhoB overexpression protects keratinocytes against UVB-induced apoptosis. These results indicated that RhoB is regulated upon UVB exposure by a two-step process consisting of an early EGFR-independent RhoB activation followed by an EGFR-dependent induction of RhoB expression. Moreover, we have demonstrated that RhoB is essential in regulating keratinocyte cell survival after UVB exposure, suggesting its potential role in photocarcinogenesis.

Received for publication, August 5, 2005 , and in revised form, November 4, 2005.

^* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains five supplemental figures.

¹ To whom correspondence should be addressed. Tel.: 33-5-61424131; Fax: 33-5-61424631; E-mail: favre{at}icr.fnclcc.fr.

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