Inositol hexakisphosphate kinase-1 mediates assembly/disassembly of the CRL4–signalosome complex to regulate DNA repair and cell death

• Published in: Proceedings of the National Academy of Sciences - PNAS 2014-11, Vol.111 (45), p.16005-16010
• Main Authors: Rao, Feng, Xu, Jing, Khan, A. Basit, Gadalla, Moataz M., Cha, Jiyoung Y., Xu, Risheng, Tyagi, Richa, Dang, Yongjun, Chakraborty, Anutosh, Snyder, Solomon H.
• Format: Article
• Language: English
• Subjects: Animals; Apoptosis; Binding sites; Biological Sciences; Carrier Proteins - genetics; Carrier Proteins - metabolism; Cell Death - radiation effects; COP9 Signalosome Complex; Cullin Proteins - genetics; Cullin Proteins - metabolism; Culling; Diphosphates; DNA damage; DNA repair; DNA Repair - radiation effects; Gene expression regulation; HEK293 Cells; Humans; Inositols; Kinases; Mice; Multiprotein Complexes - genetics; Multiprotein Complexes - metabolism; Peptide Hydrolases - genetics; Peptide Hydrolases - metabolism; Phosphotransferases (Phosphate Group Acceptor) - genetics; Phosphotransferases (Phosphate Group Acceptor) - metabolism; Receptors; Signal Transduction - radiation effects; Ubiquitin-Protein Ligases - genetics; Ubiquitin-Protein Ligases - metabolism; Ubiquitins; Ultraviolet Rays - adverse effects
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1417900111

Inositol polyphosphates containing an energetic pyrophosphate bond are formed primarily by a family of three inositol hexakisphosphate (IP6) kinases (IP6K1–3). The Cullin-RING ubiquitin ligases (CRLs) regulate diverse biological processes through substrate ubiquitylation. CRL4, comprising the scaffold Cullin 4A/B, the E2-interacting Roc1/2, and the adaptor protein damage-specific DNA-binding protein 1, is activated by DNA damage. Basal CRL4 activity is inhibited by binding to the COP9 signalosome (CSN). UV radiation and other stressors dissociate the complex, leading to E3 ligase activation, but signaling events that trigger signalosome dissociation from CRL4 have been unclear. In the present study, we show that, under basal conditions, IP6K1 forms a ternary complex with CSN and CRL4 in which IP6K1 and CRL4 are inactive. UV dissociates IP6K1 to generate IP7, which then dissociates CSN–CRL4 to activate CRL4. Thus, IP6K1 is a novel CRL4 subunit that transduces UV signals to mediate disassembly of the CRL4–CSN complex, thereby regulating nucleotide excision repair and cell death. Significance Attachment of the small protein ubiquitin to other proteins, a process called “ubiquitylation,” triggers protein degradation. The Cullin and signalosome protein families cooperatively mediate this process, but how they are regulated has been obscure. We show that an inositol polyphosphate with seven phosphates, hence designated IP7, is critical. Under basal conditions, the enzyme that generates IP7 is bound to the Cullin/signalosome complex, which is thereby maintained in an inactive state. Stressful stimuli, such as UV radiation, stimulate the enzyme to form IP7, which dissociates the complex, leading to activation of the Cullins with attendant ubiquitylation and degradation of target proteins. This process may play a key role in how cells respond to environmental stressors.