Localization of interferon regulatory factor-1 (IRF-1) in nonpregnant human endometrium: Expression of IRF-1 is up-regulated by prolactin during the secretory phase of the menstrual cycle

PRL expression in the human uterus is up-regulated during the mid to late s ecretory phase of the menstrual cycle. This coincides with up-regulation of the expression of the PRL receptor, which is localized primarily to the en dometrial glandular epithelial cells. Recent data have demonstrated activat ion of the Jab (Janus kinase)/Stat (signal transducer and activator of tran scription) signaling pathway in the secretory endometrium after stimulation with exogenous PRL. However, the target genes for the action of PRL on the endometrial epithelial cells have not been elucidated. In this study we ha ve investigated the pattern/site of expression of the transcription factor interferon regulatory factor-1 (IRF-1) as well as the effect of exogenous P RL on the transcription of IRF-1 in the human endometrium during the mid to late secretory phase of the menstrual cycle. Expression of the IRF-1 gene was confirmed by RNase protection assays using a 260-bp homologous [alpha-P -32]UTP-labeled IRF-1 complementary ribonucleic acid (RNA) probe and 10 mu g total RNA extracted from human endometrium (n = 5) collected between days 19 and 26 of the menstrual cycle. Northern and Western blot analyses were conducted on secretory phase human endometrium (n = 3) using human [alpha-P -32]dCTP-labded IRF-1 complementary DNA and antihuman IRF-1 antibody. Expre ssion of the IRF-1 gene in the secretory phase endometrium was encoded by a RNA transcript of approximately 2.1 kb and a protein of 48 kDa. Furthermor e, expression of the IRF-1 gene in the secretory phase endometrium was loca lized by immunohistochemistry predominantly to the glandular epithelial cel ls as has been shown previously for the PRL receptor. To investigate the ef fect of PRL on expression of IRF-1, human endometrial biopsies (n = 3) coll ected between days 24-26 of the menstrual cycle were cultured in the presen ce of cycloheximide with or without 100 ng/mL human PRL for 2 and 4 h. Cult ure of endometrial tissue with PRL for 2 and 4 h resulted in 2.9 +/- 0.3-fo ld (P < 0.01) and 1.7 +/- 0.1-fold induction of expression of the IRF-1 gen e, respectively. These data demonstrate the expression of the transcription factor IRF-1 in the glandular epithelium of the endometrium and its regula tion by PRL during the secretory phase of the menstrual cycle. Previous obs ervations of the temporal up-regulation of expression of both PRL and PRL r eceptors in the secretory human endometrium and their localization to the s tromal and glandular compartments, respectively, suggest that endometrial P RL mediates transcription of the IRF-1 gene in a paracrine fashion.