Hepatocyte Nuclear Factor 4 Is a Transcription Factor that Constitutively Binds Fatty Acids

Abstract

The 2.7 A X-ray crystal structure of the HNF4gamma ligand binding domain (LBD) revealed the presence of a fatty acid within the pocket, with the AF2 helix in a conformation characteristic of a transcriptionally active nuclear receptor. GC/MS and NMR analysis of chloroform/methanol extracts from purified HNF4alpha and HNF4gamma LBDs identified mixtures of saturated and cis-monounsaturated C14-18 fatty acids. The purified HNF4 LBDs interacted with nuclear receptor coactivators, and both HNF4 subtypes show high constitutive activity in transient transfection assays, which was reduced by mutations designed to interfere with fatty acid binding. The endogenous fatty acids did not readily exchange with radiolabeled palmitic acid, and all attempts to displace them without denaturing the protein failed. Our results suggest that the HNF4s may be transcription factors that are constitutively bound to fatty acids.

Signalling cross-talk between hepatocyte nuclear factor 4α and growth-hormone-activated STAT5b

“…ligandindependent) nuclear receptor. Structural studies have revealed the presence of a previously unrecognized fatty acid docked in the ligand-binding domain of HNF4α [31,32], consistent with the finding that fatty acids regulate HNF4α-dependent gene expression [52,53]. Fatty acids may also modulate STAT5 activity [54,55].…”

“…Structural studies have revealed that fatty acids serve as endogenous ligands of HNF4α [31,32]. Moreover, short-chain fatty acids, such as butyrate, can enhance GH-induced STAT5b activity [33].…”

A Mediator subunit, MDT-15, integrates regulation of fatty acid metabolism by NHR-49-dependent and -independent pathways inC. elegans

“…It is tempting to speculate that such up-regulation might be achieved through increased association of MDT-15 with the NHR-49-LBD, perhaps driven by binding of the receptor to a hormone-like small molecule(s) whose levels fluctuate in response to food availability. It may be significant in this regard that specific FAs associate with the LBD of HNF4␣ (Hertz et al 1998;Wisely et al 2002). Thus, nutrient availability may signal to NHR-49:MDT-15 regulatory complexes to modulate a sector of metabolic gene expression.…”

Role of Regulatory F-domain in Hepatocyte Nuclear Factor-4α Ligand Specificity

“…1) (8,(11)(12)(13)(14)(15)(16). The molecular basis for this constitutive activity remains to be determined but may include ligand-based mechanisms involving dietary or endogenous long chain fatty acids (LCFA) (17,18), endogenously synthesized coenzyme A (CoA) thioesters of long chain fatty acids (LCFA-CoAs) (8,11,14,19), and/or the F-domain itself functioning as a modulator (16).…”