title: WD40 protein FBW5 promotes ubiquitination of tumor suppressor TSC2 by DDB1-CUL4-ROC1 ligase.
abstract: Tuberous sclerosis (TSC) is an autosomal dominant disease characterized by hamartoma formation in various organs and is caused by mutations targeting either the TSC1 or TSC2 genes. TSC1 and TSC2 proteins form a functionally interdependent dimeric complex. Phosphorylation of either TSC subunit by different kinases regulates the function of TSC and represents a major mechanism to integrate various signals into a centralized cell growth pathway. The majority of disease-associated mutations targeting either TSC1 or TSC2 results in a substantial decrease in protein level, suggesting that protein turnover also plays a critical role in TSC regulation. Here we report that TSC2 protein binds to FBW5, a DDB1-binding WD40 (DWD) protein, and is recruited by FBW5 to the DDB1-CUL4-ROC1 E3 ubiquitin ligase. Overexpression of FBW5 or CUL4A promotes TSC2 protein degradation, and this is abrogated by the coexpression of TSC1. Conversely, depletion of FBW5, DDB1, or CUL4A/B stabilizes TSC2. Ddb1 or Cul4 mutations in Drosophila result in Gigas/TSC2 protein accumulation and cause growth defects that can be partially rescued by Gigas/Tsc2 reduction. These results indicate that FBW5-DDB1-CUL4-ROC1 is an E3 ubiquitin ligase regulating TSC2 protein stability and TSC complex turnover.
authors.affiliation: Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
authors.forename: Jian
authors.initials: J
authors.lastname: Hu
authors.forename: Sima
authors.initials: S
authors.lastname: Zacharek
authors.forename: Yizhou Joseph
authors.initials: YJ
authors.lastname: He
authors.forename: Hyun
authors.initials: H
authors.lastname: Lee
authors.forename: Stuart
authors.initials: S
authors.lastname: Shumway
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Duronio
authors.forename: Yue
authors.initials: Y
authors.lastname: Xiong
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D045744:Cell Line, Tumor; D044842:Cullin Proteins / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004330:Drosophila / Q000235:genetics / Q000254:growth & development / Q000648:ultrastructure; D004591:Electrophoresis, Polyacrylamide Gel; D044783:F-Box Proteins / Q000235:genetics / Q000378:metabolism*; D005816:Genetic Complementation Test; D006367:HeLa Cells; D006801:Humans; D008025:Ligases / Q000235:genetics / Q000378:metabolism; D008855:Microscopy, Electron, Scanning; D009154:Mutation; D010766:Phosphorylation; D011485:Protein Binding; D034622:RNA Interference; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*; D020798:Two-Hybrid System Techniques; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism; D015003:Yeasts / Q000235:genetics
chemical_list: C114234:CUL4A protein, human; D002352:Carrier Proteins; D044842:Cullin Proteins; C091435:DDB1 protein, human; D004268:DNA-Binding Proteins; D044783:F-Box Proteins; C528759:FBXW5 protein, human; C479529:RBX1 protein, human; C000624653:TSC2 protein, human; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D025801:Ubiquitin; D044767:Ubiquitin-Protein Ligases; D008025:Ligases