Differences in Prolactin Receptor (PRLR) in Mouse and Human Fallopian Tubes: Evidence for Multiple Regulatory Mechanisms Controlling PRLR Isoform Expression in Mice

BIOLOGY OF REPRODUCTION 79, 748–757 (2008) Published online before print 2 July 2008. DOI 10.1095/biolreprod.108.070003 Differences in Prolactin Receptor (PRLR) in Mouse and Human Fallopian Tubes: Evidence for Multiple Regulatory Mechanisms Controlling PRLR Isoform Expression in Mice1 Ruijin Shao,2,3,4 Magdalena Nutu,3,4 Birgitta Weijdegård,4 Emil Egecioglu,4 Julia Fernandez-Rodriguez,5 Estelle Tallet,6,7 Vincent Goffin,6,7 Charlotte Ling,8 and Håkan Billig4 comparative study provide evidence that PRLR can be regulated by an interplay of two different mechanisms, PRL or ovarian steroid hormones independently or in combination in a tissuespecific manner. Furthermore, we found that ovarian steroid hormones selectively suppress the expression of PRLR isoforms in mouse fallopian tubes. These findings may contribute to our understanding of the mechanisms controlling PRLR isoform expression in the fallopian tube (in addition to ovary and uterus), with implications for female reproduction. ABSTRACT The anterior pituitary-derived hormone prolactin (PRL) signals through the PRL receptor (PRLR) and is important for female reproductive function in mammals. In contrast to the extensive studies of PRLR expression and regulation in human and mouse ovary and uterus, the mechanisms controlling the regulation of PRLR isoform expression in the fallopian tube are poorly understood. Because dynamic interaction of hormonal signaling in gonadal tissue and the pituitary or in gonadal tissues themselves in mammals suggests endocrine or paracrine regulation of PRLR expression, we questioned whether differential regulation of PRLR isoforms by PRL ovarian-derived estrogen (E2) and progesterone (P4) exists in the fallopian tube and pituitary of prepubertal female mice. Western blot analysis showed distinct molecular separation of PRLR isoforms in mouse and human fallopian tubes, and cellular localization was found in mouse and human tubal epithelia but not in mouse tubal smooth muscle cells. These data support the concept of an isoform- and cell type-specific expression of PRLR in human and mouse fallopian tubes. Moreover, expression of the long form of PRLR decreased after PRL treatment and increased after blockage of endogenous PRL secretion by bromocriptine (an inhibitor of PRL secretion) in a time-dependent manner in mouse fallopian tube. The opposite regulation was observed in the pituitary. Treatment with exogenous E2 or P4 led to changes in PRLR expression in the fallopian tube similar to those of PRL treatment. However, E2 and P4 did not affect PRLR expression in the pituitary. Estrogen had no effect on the long form of PRLR expression, whereas P4 regulated the long form of PRLR in the fallopian tube, as did PRL. Taken together, the data from our estradiol, fallopian tube, ovarian steroid hormones, oviduct, pituitary, prolactin, prolactin receptor, prolactin receptor isoforms INTRODUCTION Prolactin (PRL), which is synthesized and secreted by the anterior pituitary gland (primarily by lactotropes [1]), participates in the regulation of female reproductive function in humans and rodents [2, 3]. The diverse biological actions of PRL are mediated through its cognate receptor, the transmembrane PRL receptor (PRLR), which is a member of the cytokine receptor superfamily that initiates signal transduction pathways and results in a series of coordinated physiological events in target endocrine tissues [4, 5]. Reported effects of PRL provide evidence for the importance of this hormone and PRLR on female fertility. For instance, hyperprolactinemia, a pathological condition, has been linked to a reduction of fertility due to disturbances in ovarian function in women [6] and inhibition of embryo implantation in mice [7]. Moreover, treatment with bromocriptine (an inhibitor of PRL secretion [8]) can reverse infertility induced by prolactinomas (lactotroph adenomas) in young women [9]. Although it has become clear that elevation of circulating PRL suppresses fertility in mice [10], targeted disruption of PRLR in female mice results in reduced fertility, uteri refractory to implantation [11, 12], and increased circulating PRL level [12, 13], highlighting that loss of function in PRL and PRLR signaling is the primary reason for the reproductive disorders seen in these animals. Prolactin binding to the PRLR leads to rapid activation of receptor-associated signal transduction pathways [4, 5]. In humans, PRLR can also be activated in a PRL-independent fashion [14]. Multiple PRLR isoforms generated by alternative exon splicing of the PRLR gene have been identified in mammals [1, 2, 4]. The different isoforms in mice (long and short forms) and humans (long, intermediate, and short forms) 1 Supported by Svenska Sällskapet för Medicinsk Forskning, Sahlgrenska Academy Research Council, Göteborgs Läkaresällskap, and Fred G. and Emma E. Kanolds Stiftelse, Hjalmar Svenssons Research Foundation to R.S.; by Rådman and Fru Colliander, Emil and Maria Palm, and Eva and Oscar Ahréns Research Foundations to M.N.; and by grant 10380 from the Swedish Medical Research Council to H.B. 2 Correspondence: FAX: 46 31 7733512; e-mail: 3 These authors contributed equally to this work. Received: 16 April 2008. First decision: 6 May 2008. Accepted: 19 June 2008. Ó 2008 by the Society for the Study of Reproduction, Inc. ISSN: 0006-3363. http://www.biolreprod.org 748 Department of Physiology/Endocrinology,4 Institute of Neuroscience and Physiology, The Sahlgrenska Academy at Gothenburg University, SE-41390 Gothenburg, Sweden Center for Cellular Imaging,5 Core Facilities, The Sahlgrenska Academy at Gothenburg University, SE-41390 Gothenburg, Sweden Institut National de la Santé et de la Récherche Médicale,6 Unité 845, Centre de Recherche ‘‘Croissance et Signalisation,’’ Equipe ‘‘PRL, GH et Tumeurs,’’ F-75015 Paris, France Faculté de Médecine,7 Université Paris Descartes, F-75015 Paris, France Department of Clinical Science,8 Lund University, CRC, University Hospital MAS, SE-20502 Malmö, Sweden PRLR ISOFORM EXPRESSION IS REGULATED BY MULTIPLE HORMONES 749 TABLE 1. Detailed antibody information. Antibodya Species Clone Usageb Dilutionc Commercial source PRLR Mouse U5 Mouse Mouse Mouse Rabbit Mouse Rabbit Rabbit Mouse C-11 1A4 AC-15 MC-20 EMR02 C-19 C-20 PC10 5 lg/ml 10 lg/ml 1:1000 1:1000 1:1000 1:200 1:500 1:250 1:250 1:500 Affinity BioReagents Inc., Golden, CO ACTA2 (pan-cytokeratin) ACTA2 (a-SM actin) ACTB (b-actin) ESR1 (ERa) ESR2 (ERb) PR PR PCNA WB IHC WB WB WB WB WB WB WB WB a b c Sigma-Aldrich, St. Louis, MO Sigma Sigma Santa Cruz Biotechnologies Inc., Santa Cruz, CA Novocastra Co., United Kingdom Santa Cruz Biotechnologies Inc. Santa Cruz Biotechnologies Inc. Novocastra Co. have identical extracellular ligand-binding and transmembrane domains but varying intracellular domains [2], suggesting that the maintenance of cellular responsiveness to PRL signals may differ between mice an (...truncated)