Transcriptional Regulation of Human and Mouse Organic Anion Transporter 1 by Hepatocyte Nuclear Factor 1 α/β

Abstract

Organic anion transporter 1 (OAT1/SLC22A6) is predominantly expressed in the proximal tubules of the kidney. Cumulative studies have shown its critical role in the tubular secretion of a variety of organic anions, including several clinically important drugs. In addition, OAT1 is also involved in the pharmacological effect of diuretics and the nephrotoxicity of antiviral drugs. In contrast to these functional characterizations, the regulatory mechanism of OAT1 expression is poorly understood. It was recently demonstrated that the expression of Oat1 was markedly reduced in the kidneys of hepatocyte nuclear factor 1␣ (Hnf1␣)-null mice. However, in vitro evidence for the involvement of HNF1␣ and further analyses are required to illustrate the transcriptional regulation of OAT1 genes in more detail. Computational analysis of the potential transcription factor binding sites revealed that the HNF1-motif was conserved in the proximal-promoter region of human and mouse OAT1 genes. The mRNA expression of mouse organic anion transporter 1 was drastically reduced in Hnf1␣-null mice compared with that in wild-type mice, which was consistent with a previous report (Maher et al., 2006). Forced expression of HNF1␣ alone or both HNF1␣ and HNF1␤ enhanced the activity of human and mouse OAT1 promoters in the transactivation assays, whereas HNF1␤ alone was not active. Mutations in the HNF1-motif significantly reduced this transactivation. Direct binding of HNF1␣/HNF1␣ homodimer and HNF1␣/HNF1␤ heterodimer to the HNF1-motif found in the human OAT1 promoter was demonstrated by electrophoretic mobility shift assays. These results provide convincing evidence for the involvement of HNF1␣/␤ in the constitutive expression of human and mouse OAT1 in the kidney.

Single nucleotide polymorphisms in the human corticosteroid-binding globulin promoter alter transcriptional activity

“…Taken together with previously discussed 54 C/T and 161 A/G which affected basal promoter activity, the first four polymorphisms located within the first ~160 bp in 5′-flanking region either affect basal transcription activity or HNF1 transactivation. Moreover, our data demonstrated no functional effect of HNF1 on HNF1-stimulated promoter activity, as previously reported by others [36][37][38]. Therefore, the significant in vivo reduction of CBG biosynthesis during inflammation is likely associated with decreased binding activity of HNF1 to Cbg promoter and subsequently decreased gene transcription initiation, and promoter SNPs might be associated with different inflammatory response among different individuals.…”

Organic anion transporters: discovery, pharmacology, regulation and roles in pathophysiology

“…Supporting this finding, HNF1a overexpression in vitro enhanced mOat1 and hOAT1 promoter activity [95]. Finally, HNF1a/HNF1a or HNF1a/HNF1b dimers were shown to bind to an HNF1 motif in the hOAT1 promoter [95]. In a similar study, HNF4a activated the hOAT1 promoter, and essential binding domains for HNF4a were identified in the 5 untranslated region at À1191 to À700 bp and À140 to À79 bp [96].…”

“…To this regard, HNF1a deletion in mice was demonstrated to markedly reduce renal mOat1 mRNA levels [95]. Supporting this finding, HNF1a overexpression in vitro enhanced mOat1 and hOAT1 promoter activity [95]. Finally, HNF1a/HNF1a or HNF1a/HNF1b dimers were shown to bind to an HNF1 motif in the hOAT1 promoter [95].…”

“…Subsequent studies began to address a functional analysis of the transcription factors with respect to OAT1 and OAT3. To this regard, HNF1a deletion in mice was demonstrated to markedly reduce renal mOat1 mRNA levels [95]. Supporting this finding, HNF1a overexpression in vitro enhanced mOat1 and hOAT1 promoter activity [95].…”

Current Updates in the Genetic Polymorphisms of Human Organic Anion Transporters (OATs)

“…Nuclear Factor (HNF)-4α and other HNF isoforms, such as HNF-1α and/or ß, could activate OAT genes at the transcriptional level [32][33][34]. Likewise, OATs were also subject to the regulation of HNF-1α homodimer, HNF-1ß homodimer or HNF-1 α/ß hereodimer [35].…”