title: Association of SAP130/SF3b-3 with Cullin-RING ubiquitin ligase complexes and its regulation by the COP9 signalosome.
abstract: BACKGROUND
  Cullin-RING ubiquitin E3 ligases (CRLs) are regulated by modification of an ubiquitin-like protein, Nedd8 (also known as Rub1) on the cullin subunit. Neddylation is shown to facilitate E3 complex assembly; while un-neddylated cullins are bound by CAND1 that prevents recruitment of the substrates. The level of Nedd8 modification is critically dependent on the COP9 signalosome (CSN), an eight-subunit protein complex containing Nedd8 isopeptidase activity.
  
  
  RESULTS
  We report isolation of SAP130 (SF3b-3) as a CSN1 interacting protein. SAP130 is homologous to DDB1, and is a component of SF3b RNA splicing complex and STAGA/TFTC transcription complexes, but its specific function within these complexes is unknown. We show that SAP130 can interact with a variety of cullin proteins. It forms tertiary complexes with fully assembled CRL E3 complexes such as SCFSkp2, Elongin B/C -Cul2- VHL and Cul4-DDB complex by binding to both N-terminal and C-terminal domain of cullins. SAP130 preferentially associates with neddylated cullins in vivo. However knock-down of CAND1 abolished this preference and increased association of SAP130 with Cul2. Furthermore, we provide evidence that CSN regulates SAP130-Cul2 interaction and SAP130-associated polyubiquitinating activity.
  
  
  CONCLUSIONS
  SAP130 is a cullin binding protein that is likely involved in the Nedd8 pathway. The association of SAP130 with various cullin member proteins such as Cul1, Cul2 and Cul4A is modulated by CAND1 and CSN. As an established component of transcription and RNA processing complexes, we hypothesis that SAP130 may link CRL mediated ubiquitination to gene expression.
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut, USA. suchithra.menon@yale.edu
authors.forename: Suchithra
authors.initials: S
authors.lastname: Menon
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Tsuge
authors.forename: Naoshi
authors.initials: N
authors.lastname: Dohmae
authors.forename: Koji
authors.initials: K
authors.lastname: Takio
authors.forename: Ning
authors.initials: N
authors.lastname: Wei
mesh_terms: D000818:Animals; D001665:Binding Sites; D000075686:COP9 Signalosome Complex; D002460:Cell Line; D044842:Cullin Proteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D051379:Mice; D046912:Multiprotein Complexes / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism*; D025821:Polyubiquitin / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D016601:RNA-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D011817:Rabbits; D013379:Substrate Specificity; D014157:Transcription Factors / Q000378:metabolism; D014452:Ubiquitins / Q000378:metabolism
chemical_list: C486317:CAND1 protein, human; D044842:Cullin Proteins; D046912:Multiprotein Complexes; D016601:RNA-Binding Proteins; D014157:Transcription Factors; D014452:Ubiquitins; D025821:Polyubiquitin; D010447:Peptide Hydrolases; D000075686:COP9 Signalosome Complex