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Regulation of CCT nuclear export and degradation by monoubiquitination
Author(s) -
Chen Bill,
Mallampalli Rama K
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.807.17
Subject(s) - ubiquitin , skp1 , ubiquitin ligase , proteasome , ubiquitin conjugating enzyme , biology , cullin , microbiology and biotechnology , endosome , f box protein , protein degradation , dna ligase , biochemistry , enzyme , intracellular , gene
CTP:phosphocholine cytidylyltransferase (CCT), is an essential enzyme for phosphatidylcholine biosynthesis. CCT is also a nuclear enzyme that is proteolytically sensitive. We previously demonstrated that CCT availability is regulated by the ubiquitin‐proteasome pathway, and that tumor necrosis factor alpha (TNFalpha) induces CCT ubiquitination and degrades CCT (J. Biol. Chem. 275:2000). Herein, we demonstrate that CCT does not undergo polyubiquitination and degradation by the 26S proteasome, but rather the enzyme is monoubiquitinated, undergoes nuclear export, and subsequently is degraded in the endosome. The endosomal inhibitor ammonium chloride effectively blocked TNFalpha degradation of CCT. A CCT‐ubiquitin fusion protein that mimics monoubiquitinated CCT was found to accumulate in the endosome, indicating that monoubiquitination is critical for CCT trafficking and degradation. Mass spectrometry of the ubiquitinated CCT complex indicated thatCullin1, serves as a putative E3 ligase for CCT. Cullin1 recruits Skp1 and F‐box proteins to form an E3 complex, termed SCF. Both Cullin1 and Skp1 co‐immunoprecipitated with CCT in human lung epithelial cells. These results reveal the CCT monoubiquitination is a regulated process by distinct molecular factors that govern availability of this critical enzyme in vivo.