The Prostate 68:610 ^ 619 (2008) Triiodothyronine Modulates Cell Proliferation of Human Prostatic Carcinoma Cells by Downregulation of the B-Cell Translocation Gene 2 Ke-Hung Tsui, 1,2 Wen-Chi Hsieh, 3 Mei-Hsien Lin, 3 Phei-Lang Chang, 1 and Horng-Heng Juang 2,3 * 1 Department of Urology,Chang Gung Memorial Hospital, Kwei-Shan,Tao-Yuan,Taiwan, R.O.C. 2 Molecular Image Center,Chang Gung Memorial Hospital, Kwei-Shan,Tao-Yuan,Taiwan, R.O.C. 3 Department of Anatomy,Chang Gung University, Kwei-Shan,Tao-Yuan,Taiwan, R.O.C. BACKGROUND. Studies suggest that triiodothyronine (T3) and cognate nuclear receptors (hTR) are involved in regulation of prostatic cell growth and differentiation. To probe mechanisms for T3 effects, we studied prostate carcinoma cells, investigating the effect of T3 on expression of the B-cell translocation gene 2 (BTG2), which regulates the G1/S transition of the cell cycle. METHODS. Effects of T3 on cell proliferation were determined by 3 H-thymidine incorpo- ration. T3 modulation of BTG2 expression was investigated using immunoblots, Northern blots, and transient gene expression assays. The putative T3 response element was determined by electrophoretic mobility shift assay. RESULTS. T3 (0.1 – 1,000 nM) enhanced threefold the proliferation of prostate carcinoma cells and human androgen-dependent prostate carcinoma cells (LNCaP), but not PC-3 cells. T3 also inhibited BTG2 gene expression in LNCaP cells. Reporter assays showed that T3 downregulates by 50% promoter activity of the BTG2 gene in LNCaP cells but not PC-3 cells or thyroid-hormone receptor (TRb1)-overexpression PC-3 cells. Deleting the putative thyroid hormone response element (TRE; AGCGATGACCTCAGCG) blocked the inhibitory effect of T3 on BTG2 promoter activity. Electrophoretic mobility shift assays with purified TRb1 from in vitro translation, or with nuclear extracts from LNCaP cells and PC-3 cells, demonstrated the presence of T3 receptor binding sites in the TRE region. CONCLUSIONS. These results suggested that the T3 upregulates proliferation of LNCaP cells by downregulating BTG2 gene expression through the consensus TRE pathway. Prostate 68: 610–619, 2008. # 2008 Wiley-Liss, Inc. KEY WORDS: BTG2; LNCaP; proliferation; triiodothyronine; TRE; PC-3 INTRODUCTION Although thyroid hormone is an important regulator of growth and differentiation in many cell types, the critical influence of thyroid hormone on the growth and development of the reproductive system are, as yet, not well understood [1]. An early study suggested that thyroid hormone contributes to the regulation of benign prostatic hyperplasia (BPH) and prostate cancer [2]. A recent study indicates that men with BPH or prostate cancer have significantly elevated serum triiodothyro- nine (T3) levels [3,4]. However, the direct effect of thyroid hormone on human prostate is still not well known. Grant sponsor: Chang Gung Memorial Hospital; Grant numbers: CMRP-G34026, CMRP-D150191; Grant sponsor: National Science Council (Taiwan, ROC); Grant numbers: 95-2320-B-037-MY2, 96- 2314-B-182A-016-MY2. *Correspondence to: Dr. Horng-Heng Juang, Department of Anatomy, Chang Gung University, 259 Wen-Hua 1st Road, Kwei-Shan, Tao-Yuan 333, Taiwan, R.O.C. E-mail: hhj143@mail.cgu.edu.tw Received 12 July 2007; Accepted 15 November 2007 DOI 10.1002/pros.20725 Published online 14 January 2008 in Wiley InterScience (www.interscience.wiley.com). ß 2008 Wiley-Liss, Inc.