The deubiquitinating enzyme Fam interacts with and stabilizes beta-catenin.
BACKGROUND
In the ubiquitin-proteasome pathway, the ubiquitinated substrates either undergo degradation by the proteasome or stabilization through the action of the deubiquitinating enzyme. We have previously found that the deubiquitinating enzyme Fam is colocalized with AF-6, one of the effectors of the Ras small GTPase, at cell-cell contact sites in epithelial cells and interacts with AF-6 in vivo and in vitro. Fam has deubiquitinating activity in vitro and prevents the ubiquitination of AF-6 in intact cells. The degradation of beta-catenin, which accumulates at the cell-cell contact sites as a cadherin/catenin complex, is thought to be regulated by the ubiquitin-proteasome pathway. These observations prompted us to examine the possible Fam regulation of the stabilization of beta-catenin.


RESULTS
We found that Fam interacted with beta-catenin both in vivo and in vitro. The Fam-binding site of beta-catenin mapped to the region close to the APC or Axin-binding site of beta-catenin. Over-expression of Fam in mouse L cells resulted in an elevation of beta-catenin levels and in an elongation of the half-life of beta-catenin. In these L cells, Fam was colocalized with beta-catenin at the dot-like structures in the cytoplasm.


CONCLUSIONS
These results indicate that Fam interacts with and stabilizes beta-catenin in vivo, presumably through the deubiquitination of beta-catenin.
Taya
S
S
Division of Signal Transduction, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma 630-0101, Japan.
Yamamoto
T
T
Kanai-Azuma
M
M
Wood
S A
SA
Kaibuchi
K
K
D000818:Animals; D001665:Binding Sites; D015820:Cadherins / Q000737:chemistry / Q000378:metabolism; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000378:metabolism*; D004285:Dogs; D010450:Endopeptidases / Q000737:chemistry / Q000378:metabolism*; D016547:Kinesins / Q000378:metabolism; D007700:Kinetics; D007739:L Cells; D007976:Leupeptins / Q000494:pharmacology; D051379:Mice; D009097:Multienzyme Complexes / Q000378:metabolism; D009218:Myosins / Q000378:metabolism; D009842:Oligopeptides / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D015534:Trans-Activators; D014162:Transfection; D043222:Ubiquitin Thiolesterase; D014452:Ubiquitins / Q000378:metabolism; D051176:beta Catenin; D018631:ras Proteins / Q000378:metabolism
C490657:Afdn protein, mouse; C495267:CTNNB1 protein, mouse; D015820:Cadherins; D015853:Cysteine Proteinase Inhibitors; D003598:Cytoskeletal Proteins; D007976:Leupeptins; D009097:Multienzyme Complexes; D009842:Oligopeptides; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators; D014452:Ubiquitins; D051176:beta Catenin; C063261:acetylleucyl-leucyl-norleucinal; C069861:calpain inhibitor 2; D010450:Endopeptidases; D043222:Ubiquitin Thiolesterase; C404328:Usp9x protein, mouse; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D009218:Myosins; D016547:Kinesins; D018631:ras Proteins