The transcriptional activity of hepatocyte nuclear factor 4 alpha is inhibited via phosphorylation by ERK1/2.

ABSTRACT: Hepatocyte nuclear factor 4 alpha (HNF4?) nuclear receptor is a master regulator of hepatocyte development, nutrient transport and metabolism. HNF4? is regulated both at the transcriptional and post-transcriptional levels by different mechanisms. Several kinases (PKA, PKC, AMPK) were shown to phosphorylate and decrease the activity of HNF4?. Activation of the ERK1/2 signalling pathway, inducing proliferation and survival, inhibits the expression of HNF4?. However, based on our previous results we hypothesized that HNF4? is also regulated at the post-transcriptional level by ERK1/2. Here we show that ERK1/2 is capable of directly phosphorylating HNF4? in vitro at several phosphorylation sites including residues previously shown to be targeted by other kinases, as well. Furthermore, we also demonstrate that phosphorylation of HNF4? leads to a reduced trans-activational capacity of the nuclear receptor in luciferase reporter gene assay. We confirm the functional relevance of these findings by demonstrating with ChIP-qPCR experiments that 30-minute activation of ERK1/2 leads to reduced chromatin binding of HNF4?. Accordingly, we have observed decreasing but not disappearing binding of HNF4? to the target genes. In addition, 24-hour activation of the pathway further decreased HNF4? chromatin binding to specific loci in ChIP-qPCR experiments, which confirms the previous reports on the decreased expression of the HNF4a gene due to ERK1/2 activation. Our data suggest that the ERK1/2 pathway plays an important role in the regulation of HNF4?-dependent hepatic gene expression.

SUBMITTER: Veto B 

PROVIDER: S-EPMC5308853 | biostudies-literature | 2017

REPOSITORIES: biostudies-literature