Transcription Factor HNF4A Regulates Urate Transporter ABCG2

Abstract

Elevated urate levels in the serum can contribute to the development of many diseases, including gout, the most prevalent form of inflammatory arthritis. Our previous work identified ABCG2 as a key urate transporter of the kidney and gut epithelium and its dysfunction significantly increases risk of hyperuricemia and gout. A new collaborative meta analysis of genome wide association studies, integrating the results from 457,690 individuals, identified 183 loci associated with serum urate. A further analysis of associated loci to identify independent and potentially causal variants created a credible set of variants for experimental follow up including variants in ABCG2, HNF1A, and HNF4A. HNF1A and HNF4A are transcription factors that are key regulators of liver, renal, and gut transport proteins. Here we sought to examine if HNF1A or HNF4A regulated the expression of ABCG2, and the effects of the identified HNF1A and HNF4A missense variants. To determine any direct regulation of ABCG2 by HNF1A or HNF4A, we used a luciferase assay reporter system where the ABCG2 promoter was used to drive expression of a luciferase reporter. HEK293T cells were co‐transfected with this ABCG2 construct, and plasmids expressing either HNF1A or HNF4A, as well as a GFP reporter used to determine cell number and transfection efficiency. HNF4A increases expression of ABCG2 driven luciferase in a dose dependent and significantly reproducible manner. No increase is observed with either HNF1A co‐transfection, or in the empty vector negative control. Next, the missense mutations were examined in the same luciferase assay for both HNF1A (A98V) and HNF4A (T139I). HNF4A‐T139I demonstrated an increase in ABCG2 luciferase expression to a significantly greater extent than the wild‐type protein, again in a dose dependent and reproducible manner. The increased ABCG2 promoter activation observed with the HNF4A‐T139I was not attributable to increased abundance of the mutant protein. In addition, the HNF4A‐T139I amino acid resides in an area critical for interacting with target DNA promoter regions. Our findings that HNF4A‐T139I is a gain of function variant resulting in increased abundance of ABCG2, the primary secretory transporter, is consistent with our observation that this variant associates with decreased serum urate levels in humans. Thus, we conclude that HNF4A is likely directly regulating expression of ABCG2, and thereby influencing serum urate levels.Support or Funding InformationNIDDK R01DK114091This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.