FBXL5 modulates HIF-1α transcriptional activity by degradation of CITED2

Arch Biochem Biophys. 2015 Jun 15;576:61-72. doi: 10.1016/j.abb.2015.04.012. Epub 2015 May 5.


CITED2 is a ubiquitously expressed nuclear protein exhibiting a high affinity for the cysteine-histidine-rich domain 1 (CH1) of the transcriptional co-activators CBP/p300. CITED2 is particularly efficient in the inhibition of the hypoxia-inducible factor-1α (HIF-1α) dependent transcription by competing with it for the interaction with the CH1 domain. Here we report a direct and specific interaction between CITED2 and the F-box and leucine rich repeat protein 5 (FBXL5), a substrate adaptor protein which is part of E3 ubiquitin ligase complexes mediating protein degradation by the proteasome. We demonstrated that depletion of FBXL5 by RNA interference led to an increase of CITED2 protein levels. Conversely, overexpression of FBXL5 caused the decrease of CITED2 protein levels in a proteasome-dependent manner, and impaired the interaction between CITED2 and the CH1 domain of p300 in living cells. In undifferentiated mouse embryonic stem cells, the overexpression of FBXL5 also reduced Cited2 protein levels. Finally, we evidenced that FBXL5 overexpression and the consequent degradation of CITED2 enabled the transcriptional activity of the N-terminal transactivation domain of HIF-1α. Collectively, our results highlighted a novel molecular interaction between CITED2 and FBXL5, which might regulate the steady state CITED2 protein levels and contribute to the modulation of gene expression by HIF-1α.

Keywords: CITED2; FBXL5; HIF-1α; Mouse embryonic stem cells; Proteasome; TFAP2.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line
  • Embryonic Stem Cells / metabolism
  • F-Box Proteins / genetics
  • F-Box Proteins / metabolism*
  • HEK293 Cells
  • Humans
  • Hypoxia-Inducible Factor 1, alpha Subunit / metabolism*
  • Mice
  • Proteasome Endopeptidase Complex / metabolism
  • Protein Interaction Maps
  • Proteolysis
  • Repressor Proteins / metabolism*
  • Trans-Activators / metabolism*
  • Transcriptional Activation
  • Ubiquitin-Protein Ligase Complexes
  • Ubiquitin-Protein Ligases / genetics
  • Ubiquitin-Protein Ligases / metabolism*
  • Up-Regulation
  • p300-CBP Transcription Factors / metabolism


  • CITED2 protein, human
  • F-Box Proteins
  • FBXL5 protein, human
  • Hypoxia-Inducible Factor 1, alpha Subunit
  • Repressor Proteins
  • Trans-Activators
  • p300-CBP Transcription Factors
  • Ubiquitin-Protein Ligase Complexes
  • Ubiquitin-Protein Ligases
  • Proteasome Endopeptidase Complex