Thyroid-Stimulating Hormone Increases HNF-4α Phosphorylation via cAMP/PKA Pathway in the Liver

Abstract

Hepatocyte nuclear factor-4 alpha (HNF-4α) is an orphan nuclear receptor with important roles in hepatic metabolism. Protein phosphorylation plays a functional role in its nuclear localization, DNA binding, and transactivation. Thyroid-stimulating hormone (TSH) is a hormone produced by the anterior pituitary gland, whose direct effect on the metabolic pathway has been observed. Our previous study demonstrated that TSH significantly decreases hepatic nuclear HNF-4α expression. However, whether TSH can influence HNF-4α phosphorylation is unclear. Here, we discovered that TSH can increase HNF-4α phosphorylation and modulate its subcellularlocalization. When HepG2 cells were treated with TSH, the phosphorylation of HNF-4α increased and its nuclear localization was interrupted. Cytoplasmic HNF-4α increased, while nuclear HNF-4α decreased. When the cAMP/PKA pathway was inhibited by the PKA inhibitor H89 and the adenylate cyclase (AC) inhibitor SQ22536, the TSH-mediated phosphorylation of HNF-4α was disrupted. When Tshr was silenced in mice, the phosphorylation of HNF-4α decreased, and cytoplasmic HNF-4α decreased while nuclear HNF-4α increased. In conclusion, our study revealed a novel mechanism by which TSH regulated the hepatic HNF-4α subcellular localization, suggesting the possibility that one of the effects of TSH is to reduce the expression of HNF-4α target genes.