Identification and characterization of novel splice variants of human farnesoid X receptor

• Published in: Archives of biochemistry and biophysics 2021-07, Vol.705, p.108893, Article 108893
• Main Authors: Mustonen, Enni-Kaisa, Lee, Serene M.L., Nieß, Hanno, Schwab, Matthias, Pantsar, Tatu, Burk, Oliver
• Format: Article
• Language: English
• Subjects: Alternative Splicing; DNA binding; Dominant negative protein; Farnesoid X receptor; HEK293 Cells; Hep G2 Cells; Hepatocytes - metabolism; Humans; Molecular Dynamics Simulation; Nuclear receptor; Protein Isoforms - genetics; Protein Isoforms - metabolism; Receptors, Cytoplasmic and Nuclear - genetics; Receptors, Cytoplasmic and Nuclear - metabolism; Transactivation; Transcriptional Activation
• ISSN: 0003-9861; 1096-0384; 1096-0384
• DOI: 10.1016/j.abb.2021.108893

Farnesoid X receptor (FXR, NR1H4) is a ligand-activated nuclear receptor, which regulates bile acid, lipid and glucose metabolism. Due to these functions, FXR has been investigated as a potential drug target for the treatment of liver diseases, such as primary biliary cholangitis and non-alcoholic steatohepatitis. Based on the previously described four splice variants, it has been suggested that alternative promoter usage and splicing may have an impact on total FXR activity as a result of encoding functionally diverse variants. Here we aimed for a systematic analysis of human hepatic FXR splice variants. In addition to the previously described FXRα1–4, we identified four novel splice variants (FXRα5–8) in human hepatocytes, which resulted from previously undetected exon skipping events. These newly identified isoforms displayed diminished DNA binding and impaired transactivation activities. Isoform FXRα5, which suppressed the transactivation activity of the functional isoform FXRα2, was further characterized as deficient in heterodimerization, coactivator recruitment and ligand binding. These findings were further supported by molecular dynamics simulations, which offered an explanation for the behavior of this isoform on the molecular level. FXRα5 exhibited low uniform expression levels in nearly all human tissues. Our systematic analysis of FXR splice variants in human hepatocytes resulted in the identification of four novel FXR isoforms, which all proved to be functionally deficient, but one novel variant, FXRα5, also displayed dominant negative activity. The possible associations with and roles of these novel isoforms in human liver diseases require further investigation. •Four novel splice variants of farnesoid X receptor, FXRα5-8, were identified.•Novel isoforms display impaired transactivation and DNA-binding properties.•FXRα5 with disrupted ligand-binding domain exhibits dominant negative activity.•Molecular dynamics simulations explain FXRα5 loss-of function on the molecular level.•Dominant negative isoform FXRα5 shows low expression levels in healthy tissues.