The PRB-dependent FOXO1/IGFBP-1 axis is essential for progestin to inhibit endometrial epithelial growth

• Published in: Cancer letters Vol. 336; no. 1; pp. 68 - 75
• Main Authors: Nakamura, Mitsuhiro, Takakura, Masahiro, Fujii, Reina, Maida, Yoshiko, Bono, Yukiko, Mizumoto, Yasunari, Zhang, Xian, Kiyono, Tohru, Kyo, Satoru
• Format: Journal Article
• Language: English
• Published: Ireland Elsevier Ireland Ltd 09.08.2013; Elsevier Limited
• Subjects: Annealing; Binding Sites; Cell growth; Cell Line; Endometrial cancer; Endometrial epithelial cell; Endometrium - cytology; Endometrium - drug effects; Endometrium - pathology; Epithelial Cells - metabolism; Female; Forkhead Box Protein O1; Forkhead Transcription Factors - metabolism; FOXO1; Gene expression; Gene Expression Regulation; Growth inhibition; Hematology, Oncology and Palliative Medicine; Humans; IGFBP-1; Medroxyprogesterone Acetate - pharmacology; Oligonucleotide Array Sequence Analysis; Progestin; Progestins - metabolism; Promoter Regions, Genetic; Protein Binding; Receptors, Progesterone - metabolism; RNA, Small Interfering - metabolism; Studies; Up-Regulation; Women; Endometrial epithelial cell; IGFBP-1; Growth inhibition; Progestin; FOXO1
• ISSN: 0304-3835; 1872-7980
• DOI: 10.1016/j.canlet.2013.04.010

Abstract Progestin inhibits the growth of normal and cancerous endometria via the progesterone receptor (PR), but the distinct functions and signalings of PR subtypes have not been fully understood. The aim of the present study was to dissect the key pathways of progestin to inhibit endometrial epithelial growth. Immortalized endometrial epithelial cells (EM-E6/E7/TERT) with stable PRA or PRB expression were established and used for the experiments. In vitro growth inhibition by progestin was mainly observed in EM-E6/E7/TERT cells with PRB rather than those with PRA. RT-PCR assay confirmed that FOXO1 , a key gene for progestin action, was up-regulated by progestin in a PRB-dependent manner. cDNA microarray analysis identified IGFBP-1, which contains FOXO1 binding sites on its promoter, to be induced by medroxyprogesterone acetate (MPA) in EM-E6/E7/TERT cells with PRB but not with PRA. siRNA knockdown of FOXO1 disturbed the induction of IGFBP-1 by MPA, while IGFBP-1 knockdown showed no effect on MPA-induced FOXO1 expression, indicating that FOXO1 is an upstream regulator of IGFBP-1 . Luciferase reporter assays showed that MPA activated the IGFBP-1 promoter, which was cancelled by FOXO1 knockdown. Chromatin immunoprecipitation assay confirmed the in vivo binding of FOXO1 to the core promoter of IGFBP-1. IGFBP-1 knockdown significantly attenuated the growth inhibitory effects of MPA. The FOXO1/IGFBP-1 axis is essential for PRB-dependent growth inhibition of endometrial epithelial cells, offering a potential therapeutic clue to enhance the progestin effect.