Thyroid Hormone Positively Regulates the Enterocyte Differentiation Marker Intestinal Alkaline Phosphatase Gene via an Atypical Response Element

• DOI: 10.1210/me.2003-0351
• Publication Date: 2004-05-18T00:33:36Z
• Authors: Madhu S. Malo; Wenying Zhang; Fuad Alkhoury; Premraj Pushpakaran; Mario A. Abedrapo; Moushumi Mozumder; Elizabeth Fleming; Aleem Siddique; Joseph W. Henderson; Richard A. Hodin
• Keywords: Retinoid X receptor; Enterocyte; Hormone response element; Thyroid hormone receptor; Response element

Thyroid hormone (T3) is a critical regulator of intestinal epithelial development and homeostasis, but its mechanism action within the gut not well understood. We have examined molecular mechanisms underlying T3 activation enterocyte differentiation marker alkaline phosphatase (IAP) gene. RT-PCR Western blotting showed that thyroid receptors TRα1 TRβ1 were expressed in human colorectal adenocarcinoma Caco-2 cells. Northern detected expression two IAP transcripts, which increased approximately 3-fold response to T3. Transient transfection studies with luciferase reporter plasmids carrying various internal 5′ deletion mutations promoter localized putative element (TRE) region 620 nucleotides upstream (−620) ATG start codon. EMSAs using TRα1-retinoid X receptor α (RXRα) on sequential 3′ single nucleotide deletions defined TRE between −632 −612 (5′-TTGAACTCAgccTGAGGTTAC-3′). Compared consensus TRE, IAP-TRE novel it contains an everted repeat nonamers (not hexamers) separated by three nucleotides. Neither nor RXRα binds IAP-TRE; however, this minimal affinity. In presence TR RXRα, only TR-RXRα heterodimer IAP-TRE. Mutagenesis either nonamer abolishes biological activity promoter. thus identified appears mediate T3-induced marker, phosphatase.