Format

Send to

Choose Destination
J Biol Chem. 2007 Apr 20;282(16):11687-95. Epub 2007 Feb 12.

Protein kinase A suppresses sterol regulatory element-binding protein-1C expression via phosphorylation of liver X receptor in the liver.

Author information

1
Department of Internal Medicine, Metabolism and Endocrinology, Graduate School of Comprehensive Human Sciences and Center for Tsukuba Advanced Research Alliance, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8575, Japan.

Abstract

Sterol regulatory element-binding protein (SREBP)-1c is a transcription factor that controls synthesis of fatty acids and triglycerides in the liver and is highly regulated by nutrition and hormones. In the current studies we show that protein kinase A (PKA), a mediator of glucagon/cAMP, a fasting signaling, suppresses SREBP-1c by modulating the activity of liver X receptor alpha (LXRalpha), a dominant activator of SREBP-1c expression. Activation of PKA repressed LXR-induced SREBP-1c expression both in rat primary hepatocytes and mouse livers. Promoter analyses revealed that the LXRalpha-binding site in the SREBP-1c promoter is responsible for PKA inhibitory effect on SREBP-1c transcription. In vitro and in vivo PKA directly phosphorylated LXRalpha, and the two consensus PKA target sites (195, 196 serines and 290, 291 serines) in its ligand binding/heterodimerization domain were crucial for the inhibition of LXR signaling. PKA phosphorylation of LXRalpha caused impaired DNA binding activity by preventing LXRalpha/RXR dimerization and decreased its transcription activity by inhibiting recruitment of coactivator SCR-1 and enhancing recruitment of corepressor NcoR1. These results indicate that LXRalpha is regulated not only by oxysterol derivatives but also by PKA-mediated phosphorylation, which suggests that nutritional regulation of SREBP-1c and lipogenesis could be regulated at least partially through modulation of LXR.

PMID:
17296605
DOI:
10.1074/jbc.M611911200
[Indexed for MEDLINE]
Free full text

Supplemental Content

Full text links

Icon for HighWire
Loading ...
Support Center