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Génétique des Eucaryotes et Endocrinologie Moléculaire, UMR 6547 CNRS, Equipe Physiologie Comparée et Endocrinologie Moléculaire, Université Blaise Pascal, Campus Universitaire des Cézeaux, 24 Avenue des Landais, 63177 Aubière Cedex, France
¹ UMR 8161 Institut de Biologie de Lille/CNRS/Université de Lille 1/Université Lille2/Institut Pasteur de Lille, 1 rue Calmette, BP 447, 59021 Lille Cedex, France
² Laboratoire d’Immunologie, Centre Jean Perrin, 58 rue Montalembert, BP 392, 63011 Clermont-Ferrand, France

(Requests for offprints should be addressed to L Morel; Email: laurent.morel{at}univ-bpclermont.fr)

In the male, androgens promote growth and differentiation of sex reproductive organs through ligand activation of the androgen receptor (AR). Here, we show that androgens are not major actors of the cell cycle arrest associated with the differentiation process, and that the epidermal growth factor (EGF)-mediated signalling interferes with AR activities to regulate androgen response when epithelial cells are differentiated. Higher AR expression and enhanced androgen responsiveness correlate with reduction of phosphorylated ERK1/2 over differentiation. These modifications are associated with recruitment of cells in phase G₀/G₁, up-regulation of p27^kip1, down-regulation of p21^Cip1 and p53 proteins, and accumulation of hypo-phosphorylated Rb. Exposure to EGF reduces AR expression levels and blocks androgen-dependent transcription in differentiated cells. It also restores p53 and p21^Cip1 levels, Rb hyper-phosphorylation, ERK1/2 activation and promotes cell cycle re-entry as p27^kip1 protein levels are decreased. Treatment with a MEK inhibitor reverses the EGF-mediated AR down-regulation in differentiated cells, thus suggesting the existence of an inverse correlation between EGF and androgen signalling in non-tumoural epithelia. Interestingly, when androgen signalling is set in differentiated cells, dihydrotestosterone exerts an inhibitory effect on ERK activity but paradoxically does not modify EGFR (ErbB1) phosphorylation, indicating that androgens are able to disrupt the EGFR–ERK cascade. Overall, our data demonstrate the existence of a balance between AR and mitogen-activated protein kinase activities that favours either the maintenance of differentiated conditions or the enhancement of cell proliferation capacities.

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