Inositol hexakisphosphate (IP6) generated by IP5K mediates cullin-COP9 signalosome interactions and CRL function

Proc Natl Acad Sci U S A. 2016 Mar 29;113(13):3503-8. doi: 10.1073/pnas.1525580113. Epub 2016 Mar 14.

Abstract

The family of cullin-RING E3 Ligases (CRLs) and the constitutive photomorphogenesis 9 (COP9) signalosome (CSN) form dynamic complexes that mediate ubiquitylation of 20% of the proteome, yet regulation of their assembly/disassembly remains poorly understood. Inositol polyphosphates are highly conserved signaling molecules implicated in diverse cellular processes. We now report that inositol hexakisphosphate (IP6) is a major physiologic determinant of the CRL-CSN interface, which includes a hitherto unidentified electrostatic interaction between the N-terminal acidic tail of CSN subunit 2 (CSN2) and a conserved basic canyon on cullins. IP6, with an EC50 of 20 nM, acts as an intermolecular "glue," increasing cullin-CSN2 binding affinity by 30-fold, thereby promoting assembly of the inactive CRL-CSN complexes. The IP6 synthase, Ins(1,3,4,5,6)P5 2-kinase (IPPK/IP5K) binds to cullins. Depleting IP5K increases the percentage of neddylated, active Cul1 and Cul4A, and decreases levels of the Cul1/4A substrates p27 and p21. Besides dysregulating CRL-mediated cell proliferation and UV-induced apoptosis, IP5K depletion potentiates by 28-fold the cytotoxic effect of the neddylation inhibitor MLN4924. Thus, IP5K and IP6 are evolutionarily conserved components of the CRL-CSN system and are potential targets for cancer therapy in conjunction with MLN4924.

Keywords: COP9 signalosome; CRL; IP5K; cullin RING E3 ligases; inositol hexakisphosphate.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • COP9 Signalosome Complex
  • Catalytic Domain
  • Cullin Proteins / chemistry
  • Cullin Proteins / genetics
  • Cullin Proteins / metabolism*
  • Enzyme Stability
  • Gene Knockdown Techniques
  • HEK293 Cells
  • Humans
  • Models, Molecular
  • Molecular Sequence Data
  • Multiprotein Complexes / chemistry
  • Multiprotein Complexes / genetics
  • Multiprotein Complexes / metabolism*
  • Peptide Hydrolases / chemistry
  • Peptide Hydrolases / genetics
  • Peptide Hydrolases / metabolism*
  • Phosphotransferases (Phosphate Group Acceptor) / antagonists & inhibitors
  • Phosphotransferases (Phosphate Group Acceptor) / chemistry
  • Phosphotransferases (Phosphate Group Acceptor) / metabolism*
  • Phytic Acid / biosynthesis*
  • Protein Interaction Domains and Motifs
  • Sequence Homology, Amino Acid
  • Static Electricity
  • Ubiquitin-Protein Ligases / chemistry
  • Ubiquitin-Protein Ligases / genetics
  • Ubiquitin-Protein Ligases / metabolism

Substances

  • Cullin Proteins
  • Multiprotein Complexes
  • Phytic Acid
  • CULL-RING ligase, human
  • Ubiquitin-Protein Ligases
  • Phosphotransferases (Phosphate Group Acceptor)
  • inositol hexakisphosphate kinase
  • Peptide Hydrolases
  • COP9 Signalosome Complex
  • CRL4 protein, human