β-TrCP-mediated ubiquitination and degradation of liver-enriched transcription factor CREB-H

Sci Rep. 2016 Mar 31:6:23938. doi: 10.1038/srep23938.

Abstract

CREB-H is an endoplasmic reticulum-resident bZIP transcription factor which critically regulates lipid homeostasis and gluconeogenesis in the liver. CREB-H is proteolytically activated by regulated intramembrane proteolysis to generate a C-terminally truncated form known as CREB-H-ΔTC, which translocates to the nucleus to activate target gene expression. CREB-H-ΔTC is a fast turnover protein but the mechanism governing its destruction was not well understood. In this study, we report on β-TrCP-dependent ubiquitination and proteasomal degradation of CREB-H-ΔTC. The degradation of CREB-H-ΔTC was mediated by lysine 48-linked polyubiquitination and could be inhibited by proteasome inhibitor. CREB-H-ΔTC physically interacted with β-TrCP, a substrate recognition subunit of the SCF(β-TrCP) E3 ubiquitin ligase. Forced expression of β-TrCP increased the polyubiquitination and decreased the stability of CREB-H-ΔTC, whereas knockdown of β-TrCP had the opposite effect. An evolutionarily conserved sequence, SDSGIS, was identified in CREB-H-ΔTC, which functioned as the β-TrCP-binding motif. CREB-H-ΔTC lacking this motif was stabilized and resistant to β-TrCP-induced polyubiquitination. This motif was a phosphodegron and its phosphorylation was required for β-TrCP recognition. Furthermore, two inhibitory phosphorylation sites close to the phosphodegron were identified. Taken together, our work revealed a new intracellular signaling pathway that controls ubiquitination and degradation of the active form of CREB-H transcription factor.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Binding Sites
  • Cyclic AMP Response Element-Binding Protein / genetics*
  • Cyclic AMP Response Element-Binding Protein / metabolism
  • Gene Expression Regulation
  • HEK293 Cells
  • Hep G2 Cells
  • Humans
  • Liver / metabolism*
  • Phosphorylation
  • Proteasome Endopeptidase Complex / metabolism
  • Protein Binding
  • Protein Transport
  • Proteolysis
  • RNA, Small Interfering / genetics
  • RNA, Small Interfering / metabolism
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Signal Transduction*
  • Transcription, Genetic*
  • Ubiquitination
  • beta-Transducin Repeat-Containing Proteins / antagonists & inhibitors
  • beta-Transducin Repeat-Containing Proteins / genetics*
  • beta-Transducin Repeat-Containing Proteins / metabolism

Substances

  • CREB3L3 protein, human
  • Cyclic AMP Response Element-Binding Protein
  • RNA, Small Interfering
  • beta-Transducin Repeat-Containing Proteins
  • Proteasome Endopeptidase Complex