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Regulation of Transcription Factors and Repression of Sp1 by Prolactin Signaling Through the Short Isoform of Its Cognate Receptor

Department of Physiology and Biophysics (Y.S.D., A.S., C.S., J.H., J.L., A.M.S., M.L., G.G.), College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612; and Unité Mixte de Recherche S845 (N.B.), Faculté de Médecine René Descartes, Université Paris-Descartes, Site Necker, Paris F-75015, France

Address all correspondence and requests for reprints to: Geula Gibori, Ph.D., Department of Physiology and Biophysics, College of Medicine, University of Illinois at Chicago, 835 South Wolcott, M/C 901, Chicago, Illinois 60612. E-mail: ggibori{at}uic.edu.

Prolactin (PRL) affects the development and function of the reproductive system by binding to two types of receptors, which differ by the size of their intracellular domain in rodents. Whereas the signaling pathway through the long form of the receptor (PRL-RL) is well characterized, signaling through the short form (PRL-RS) remains obscure. In this investigation, we examined transcription factors regulated by PRL in the ovary and decidua of mice expressing only PRL-RS in a PRL receptor null background. These mice provide a powerful in vivo model to study the selective signaling mechanism of PRL through PRL-RS independent of PRL-RL. We also examined the regulation of transcription factors in ovarian and uterine cell lines stably transfected with PRL-RS or PRL-RL. We focused our investigation on transcription factors similarly regulated in both these tissues and clearly established that signaling through PRL-RS does not activate the JaK/Stat in vivo but leads to severe down-regulation of Sp1 expression, DNA binding activity, and nuclear localization, events that appear to involve the calmodulin-dependent protein kinase pathway. Our in vivo and in culture data demonstrate that the PRL-RS activates a signaling pathway distinct from that of the PRL-RL.