Transcriptional Regulation of the Rat NHE3 Gene

Abstract

Expression of sodium-hydrogen exchanger isoform 3 (NHE3) in the intestinal and renal epithelium plays a critical role in sodium absorption and acid/base homeostasis. To decipher rat NHE3 gene regulation, its cisacting regulatory elements and associated transcription factors were characterized by transient transfection of Caco-2, IEC-6, Qt6, and Drosophila SL2 cells. Deletion and mutational analyses demonstrated that the atypical TATA box located at bp ؊26/؊31 was not necessary for promoter activity, and that a ؊20/؉8-bp fragment represents a functional initiator. Within the 81-bp upstream region, three Sp transcription factor binding sites were critical because their mutation drastically reduced promoter activity. The roles of Sp1 and Sp3 were further demonstrated by electromobility shift assay and by transactivation of the NHE3 promoter in SL2 cells by forced expression of Sp1 and Sp3. Both of these transcription factors were found to act synergistically with GATA-5 bound to a GATA box in exon 1 (؉20/؉23 bp). These studies demonstrate that rat NHE3 promoter is initiator-driven and controlled mainly by Sp1 and Sp3, which functionally interact with GATA-5. This interaction represents a novel regulatory mechanism, which is likely to participate in a gradient of intestinal gene expression along the crypt-villus axis.

Characterization of the 5′-regulatory region of the human thiamin transporter SLC19A3: in vitro and in vivo studies

“…Whereas SP1 has only been implicated as an activator of transcription, SP3 is a bifunctional transcriptional regulator and can act as activator or repressor of transcription depending on the cell/promoter type (11,12,14,19). We found that in SP-deficient Drosophila SL2 cells, SP1 and SP3 were both able to stimulate transcriptional activity of the SLC19A3 minimal promoter in a dose-dependent manner.…”

“…SP1 has been shown to be primarily a positive transactivating factor (19), whereas SP3 acts as a transcription activator or a transcription repressor depending on cell/promoter type (11,12,14,19). To compare the effects of SP1 and SP3 on activity of the SLC19A3 minimal promoter, we performed cotransfection assays in Drosophila SL2 cells.…”

GATA4 regulates ANF expression synergistically with Sp1 in a cardiac hypertrophy model

“…GATA families cooperate with Sp proteins, classically thought of as part of the basal transcriptional machinery, to mediate the expression of some tissue-specific genes [14]. The Sp family contains at least four members [15, 16], all having three zinc finger binding domains located at the C-terminal region for DNA binding and varying stretches of serine/threonine domains at the N-terminal region.…”

Changes in the Rumen Papillae During the Periparturient Transition in Holstein Dairy Cows are Accompanied by Changes in Abundance of Proteins Involved in Intracellular pH Regulation, But not SCFA Transport

“…Acidotic challenges to the intracellular pH result in a rapid recovery that aims to restore pH homeostasis in the cell within 10 min (Müller et al, 2000). Several mechanisms exist to regulate intracellular pH; prominent intracellular pH-regulating include sodium proton exchangers (Kiela et al, 2003: Müller et al, 2000, which export protons from the cytosol and Carbonic Anhydrase isoform 2 (CA2), which reversibly catalyzes the carbon dioxide/bicarbonate equilibrium in the cytosol, thereby eliminating protons from the cytosol. Further, CA2 has been found to be integral to the transport of AE1, with AE1 and several other transport proteins like downregulated in adenoma, containing a CA2-attachment site in their carboxy-terminus (Sterling et al, 2001).…”