Antiproliferative proteins of the BTG/Tob family are degraded by the ubiquitin-proteasome system.
BTG/Tob family proteins, which are characterized by similarities in their N-terminal BTG/Tob homology domains, control cell growth negatively. Among the BTG/Tob family members, BTG2/TIS21/PC3 proteins have been reported to have short lives and to be degraded by the proteasome. However, the mechanisms regulating the stabilities of other BTG/Tob family proteins have not yet been clarified. Here, we report that BTG1, Tob, and Tob2 proteins, as well as BTG2 protein, are degraded by the ubiquitin-proteasome system; the degradation of Tob protein in HeLa cells and the degradation of BTG1, BTG2, Tob and Tob2 proteins transiently expressed in HEK293 cells were inhibited by treatments with proteasome-specific inhibitors. Co-expression of BTG1, BTG2, Tob, or Tob2 protein with ubiquitin in HEK293 cells revealed specific multiubiquitination of each of the four proteins. Although the full-length and N-terminal truncated forms of BTG1, BTG2, Tob, and Tob2 proteins were unstable, the respective C-terminal truncated forms were found to be almost stable, suggesting that the C-terminal regions control the stabilities of BTG1, BTG2, Tob, and Tob2 proteins. In addition, it was found that the respective C-terminal regions confer instability on green fluorescent protein, a normally stable protein. Thus, it can be concluded that the C-terminal regions are necessary and sufficient to control the stabilities of BTG1, BTG2, Tob, and Tob2 proteins.
Department of Biochemistry, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
Hitoshi
H
Sasajima
Koji
K
Nakagawa
Hideyoshi
H
Yokosawa
D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002455:Cell Division / Q000502:physiology; D002460:Cell Line; D016147:Genes, Tumor Suppressor; D049452:Green Fluorescent Proteins; D006207:Half-Life; D006367:HeLa Cells; D006801:Humans; D017874:Immediate-Early Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D007668:Kidney; D008164:Luminescent Proteins / Q000737:chemistry; D009363:Neoplasm Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism*; D011480:Protease Inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D025521:Tumor Suppressor Proteins; D025801:Ubiquitin / Q000378:metabolism*
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D017874:Immediate-Early Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008164:Luminescent Proteins; D009363:Neoplasm Proteins; D010446:Peptide Fragments; D011480:Protease Inhibitors; D011993:Recombinant Fusion Proteins; C098669:TOB1 protein, human; C402648:TOB2 protein, human; D025521:Tumor Suppressor Proteins; D025801:Ubiquitin; C070114:BTG2 protein, human; C074086:BTG1 protein, human; D049452:Green Fluorescent Proteins; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease