Defining the transcriptional regulation of the intestinal sodium-glucose cotransporter using RNA-interference mediated gene silencing.

BACKGROUND: The sodium glucose cotransporter (SGLT1) is responsible for all active intestinal glucose uptake. Hepatocyte nuclear factors 1 alpha and beta (HNF 1 alpha and HNF 1 beta) activate the SGLT1 promoter, whereas GATA-binding protein 5 (GATA-5) and caudal-type homeobox protein 2 (CDX2) regulate transcription of other intestinal genes. We investigated SGLT1 regulation by these transcription factors using promoter studies and RNA interference.
METHODS: Chinese hamster ovary (CHO) cells were transiently cotransfected with an SGLT1-luciferase promoter construct and combinations of expression vectors for HNF 1 alpha, HNF 1 beta, CDX2, and GATA-5. Caco-2 cells were stably transfected with knockdown vectors for either HNF 1 alpha or HNF 1 beta. mRNA levels of HNF 1 alpha, HNF 1 beta, and SGLT1 were determined using quantitative polymerase chain reaction (qPCR).
RESULTS: HNF 1 alpha, GATA-5, and HNF 1 beta significantly activated the SGLT1 promoter (P < .05). Cotransfection of GATA-5 with HNF 1 alpha had an additive effect, whereas HNF 1 beta and CDX2 antagonized HNF 1 alpha and GATA-5. SGLT1 expression was significantly reduced in HNF 1 alpha or HNF 1 beta knockdowns (P < .001). HNF alpha knockdown significantly reduced HNF 1 beta expression and vice versa (P < .005).
CONCLUSIONS: HNF 1 alpha and HNF 1 beta are important transcription factors for endogenous SGLT1 expression by cultured enterocytes. GATA-5 and CDX2 also regulate SGLT1 promoter activity and show cooperativity with the HNF1s. We, therefore, propose a multifactorial model for SGLT1 regulation, with interactions between HNF1, GATA-5, and CDX2 modulating intestinal glucose absorption.