Submission Number: JON-4-11-40

Abstract Number: 432

TRANSCRIPTIONAL REGULATION OF ESTROGEN RECEPTOR BY PROLACTIN.

J Frasor* ¹, T Kitamura* ³, O-K Park-Sarge ² and Geula Gibori* ¹

Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois, USA ¹
Department of Physiology, University of Kentucky, Lexington, Kentucky, USA ²
Department of Hematopoietic Factors, Institute of Medical Science, University of Tokyo, Tokyo, Japan ³

Abstract:
The rat corpus luteum is dependent on prolactin (PRL) and estradiol for its increased lifespan during pregnancy and its capacity to synthesize progesterone. These two luteotropic hormones act synergistically to stimulate progesterone production by increasing cholesterol mobilization and preventing progesterone catabolism. It has been well established that PRL or PRL-like hormones are required for the luteotropic effect of estradiol since PRL is necessary to stimulate luteal estradiol binding sites. Previously our laboratory has shown in vivo and in vitro that PRL stimulates both estrogen receptor and (ER and ER) mRNA and protein levels. Furthermore, we have reported that PRL regulates ER at the level of transcription through the Jak2/Stat5 signal transduction pathway. The purpose of this study was to examine whether PRL is able to regulate ER in a similar manner. A 1089 bp fragment of the ER promoter, subcloned into a luciferase reporter plasmid, was transfected into COS cells. In addition, COS cells were co-transfected with expression vectors for either PRL receptor long form (PRL-RL) or a constitutively active form of PRL receptor (PRL-RCA) and a Stat5b expression vector. PRL treatment of COS cells transfected with PRL-RL resulted in a two-fold stimulation of ER promoter activity. Co-transfection with PRL-RCA stimulated ER promoter activity similarly. A putative Stat5 response element located 330 bp upstream of the transcription start site was identified. Deletion of the promoter to 244 bp or 117 bp abolished PRL-RCA up-regulation of promoter activity. Regulation of ER promoter activity by PRL-RCA was specific for Stat5b since PRL-RCA had little or no effect on the promoter activity when either empty vector or an expression vector for Stat5a was co-transfected in place of Stat5b. Furthermore, co-transfection of ER promoter with a constitutively active form of Stat5b up-regulated promoter activity in the absence of PRL. In summary, we have demonstrated that PRL regulates ER at the level of transcription, through the long form of the PRL-R, and requires Stat5b. The results of this investigation indicate that PRL maintains luteal responsiveness to estradiol by stimulating transcription of both ER and ER. Supported by NIH grant HD11119 and HD12356 (GG).

Keywords: Corpus luteum, Prolactin, Estrogen Receptor

This abstract is being presented at: 2:45 PM in session:
SESSION 16: GENE EXPRESSION: TISSUE SPECIFICITY AND REGULATION OF STEROIDOGENESIS