The Human Monocarboxylate Transporter, MCT1: Genomic Organization and Promoter Analysis

Uptake of butyrate across the colonocyte luminal membrane is mediated by the monocarboxylate transporter isoform 1 (MCT1). We have demonstrated previously that expression of human colonic MCT1 is responsive to butyrate, and that this involves the dual control of MCT1 gene transcription and stability of the MCT1 transcript. Here we describe the structural organization of the human MCT1 gene, and report the isolation and characterization of the MCT1 gene promoter. The MCT1 gene spans approximately 44 kb, and is organized as 5 exons intervened by 4 introns. The first of these introns is located in the 5′-UTR-encoding DNA, spans >26 kb, and thus accounts for approximately 60% of the entire transcription unit. Analysis of a 1.5 kb fragment of the MCT1 5′-flanking region, shows an absence of the classical TATA-Box motif. However, the region contains potential binding sites for a variety of transcription factors with known association with butyrate's action in the colon. In transient transfections the 5′-flanking region drives high-level expression of a luciferase reporter-gene in cells that endogenously express MCT1. Deletion analyses indicate that the cis-acting elements necessary for basal transcription of MCT1 are contained within the −70/+213 proximal sequence of the promoter.