title: CBP and p300 are cytoplasmic E4 polyubiquitin ligases for p53.
abstract: p300 and CREB-binding protein (CBP) act as multifunctional regulators of p53 via acetylase and polyubiquitin ligase (E4) activities. Prior work in vitro has shown that the N-terminal 595 aa of p300 encode both generic ubiquitin ligase (E3) and p53-directed E4 functions. Analysis of p300 or CBP-deficient cells revealed that both coactivators were required for endogenous p53 polyubiquitination and the normally rapid turnover of p53 in unstressed cells. Unexpectedly, p300/CBP ubiquitin ligase activities were absent in nuclear extracts and exclusively cytoplasmic. Consistent with the cytoplasmic localization of its E3/E4 activity, CBP deficiency specifically stabilized cytoplasmic, but not nuclear p53. The N-terminal 616 aa of CBP, which includes the conserved Zn(2+)-binding C/H1-TAZ1 domain, was the minimal domain sufficient to destabilize p53 in vivo, and it included within an intrinsic E3 autoubiquitination activity and, in a two-step E4 assay, exhibited robust E4 activity for p53. Cytoplasmic compartmentalization of p300/CBP's ubiquitination function reconciles seemingly opposed functions and explains how a futile cycle is avoided-cytoplasmic p300/CBP E4 activities ubiquitinate and destabilize p53, while physically separate nuclear p300/CBP activities, such as p53 acetylation, activate p53.
authors.affiliation: Department of Cancer Biology, University of Massachusetts Medical School and University of Massachusetts Memorial Cancer Center, 364 Plantation Street, Worcester, MA 01605, USA.
authors.forename: Dingding
authors.initials: D
authors.lastname: Shi
authors.forename: Marius S
authors.initials: MS
authors.lastname: Pop
authors.forename: Roman
authors.initials: R
authors.lastname: Kulikov
authors.forename: Ian M
authors.initials: IM
authors.lastname: Love
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Kung
authors.forename: Andrew
authors.initials: A
authors.lastname: Kung
authors.forename: Steven R
authors.initials: SR
authors.lastname: Grossman
mesh_terms: D050882:CREB-Binding Protein / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D003593:Cytoplasm / Q000201:enzymology / Q000378:metabolism; D050881:E1A-Associated p300 Protein / Q000235:genetics / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D015151:Immunoblotting; D025821:Polyubiquitin / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism; D043743:Ubiquitin-Protein Ligase Complexes / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism
chemical_list: D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D025821:Polyubiquitin; D050882:CREB-Binding Protein; D050881:E1A-Associated p300 Protein; C494360:EP300 protein, human; D043743:Ubiquitin-Protein Ligase Complexes; C486451:UBE4A protein, human; C473697:UBE4B protein, human; D044767:Ubiquitin-Protein Ligases