title: The TRC8 ubiquitin ligase is sterol regulated and interacts with lipid and protein biosynthetic pathways.
abstract: TRC8/RNF139 encodes an endoplasmic reticulum-resident E3 ubiquitin ligase that inhibits growth in a RING- and ubiquitylation-dependent manner. TRC8 also contains a predicted sterol-sensing domain. Here, we report that TRC8 protein levels are sterol responsive and that it binds and stimulates ubiquitylation of the endoplasmic reticulum anchor protein INSIG. Induction of TRC8 destabilized the precursor forms of the transcription factors SREBP-1 and SREBP-2. Loss of SREBP precursors was proteasome dependent, required a functional RING domain, occurred without generating processed nuclear forms, and suppressed SREBP target genes. TRC8 knockdown had opposite effects in sterol-deprived cells. In Drosophila, growth inhibition by DTrc8 was genetically suppressed by loss of specific Mprlp, Padlp N-terminal domain-containing proteins found in the COP9 signalosome and eIF3. DTrc8 genetically and physically interacted with two eIF3 subunits: eIF3f and eIF3h. Coimmunoprecipitation experiments confirmed these interactions in mammalian cells, and TRC8 overexpression suppressed polysome profiles. Moreover, high-molecular weight ubiquitylated proteins were observed in eIF3 immunoprecipitations from TRC8-overexpressing cells. Thus, TRC8 function may provide a regulatory link between the lipid and protein biosynthetic pathways.
authors.affiliation: Department of Medicine and Hollings Cancer Center, Medical University of South Carolina, Charleston, South Carolina, USA.
authors.forename: Jason P
authors.initials: JP
authors.lastname: Lee
authors.forename: Anne
authors.initials: A
authors.lastname: Brauweiler
authors.forename: Michael
authors.initials: M
authors.lastname: Rudolph
authors.forename: Joan E
authors.initials: JE
authors.lastname: Hooper
authors.forename: Harry A
authors.initials: HA
authors.lastname: Drabkin
authors.forename: Robert M
authors.initials: RM
authors.lastname: Gemmill
mesh_terms: D000818:Animals; D016466:CHO Cells; D002478:Cells, Cultured; D006224:Cricetinae; D003412:Cricetulus; D004330:Drosophila; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006801:Humans; D050356:Lipid Metabolism / Q000187:drug effects / Q000235:genetics*; D053858:Metabolic Networks and Pathways / Q000187:drug effects / Q000235:genetics; D011485:Protein Binding; D014176:Protein Biosynthesis / Q000187:drug effects / Q000235:genetics*; D055550:Protein Stability / Q000187:drug effects; D011956:Receptors, Cell Surface / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D013261:Sterols / Q000494:pharmacology*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D054875:Ubiquitination / Q000235:genetics
chemical_list: C114025:RNF139 protein, human; D011956:Receptors, Cell Surface; D013261:Sterols; D044767:Ubiquitin-Protein Ligases