Posttranscriptional regulation of alpha-catenin expression is required for Wnt signaling in L cells.
alpha-Catenin is an essential component of the cadherin-catenin cell-cell adhesion complex. An excess amount of alpha-catenin also affects the Wnt signaling pathway probably through its direct binding to beta-catenin. Here, we examined the molecular mechanisms of the posttranscriptional regulation of alpha-catenin expression. We constructed an expression vector with alpha-catenin cDNA lacking the 5'-untranslated sequence. In L cell transfectants stably expressing mRNA derived from this vector, the amount of exogenous alpha-catenin protein was about 10-fold higher than that of the endogenous protein. The expression level of the exogenously expressed alpha-catenin mRNA, however, was about 80% of that of endogenous molecule. Most of the endogenous and exogenous alpha-catenin protein in cadherin-negative cells was degraded 5 h after inhibition of protein synthesis. Although alpha-catenin contains the PEST sequence, various proteasome and calpain inhibitors did not affect the level of expression of endogenous alpha-catenin protein in L cells. Overexpressed alpha-catenin showed cytoplasmic localization, disturbed the nuclear localization of stabilized beta-catenin, and inhibited TCF-4-responsive transactivation after Wnt-3a treatment. These results suggested that the low-efficiency of translation and unidentified degradation mechanisms maintained the low levels of alpha-catenin expression in the cytoplasm as a necessary condition for the Wnt signaling pathway.
Takahashi
N
N
Department of Cell Biology, Faculty of Medicine, Kyoto University, Yoshida-Konoe, Sakyo-ku, Kyoto, 606-8501, Japan.
Ishihara
S
S
Takada
S
S
Tsukita
S
S
Nagafuchi
A
A
D020121:5' Untranslated Regions / Q000235:genetics*; D000818:Animals; D015820:Cadherins / Q000502:physiology; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism; D002448:Cell Adhesion; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D007739:L Cells; D051379:Mice; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D014176:Protein Biosynthesis; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D015398:Signal Transduction; D051153:Wnt Proteins; D029961:Zebrafish Proteins; D051178:alpha Catenin
D020121:5' Untranslated Regions; D015820:Cadherins; C495272:Ctnna1 protein, mouse; D003598:Cytoskeletal Proteins; D009097:Multienzyme Complexes; D011518:Proto-Oncogene Proteins; D051153:Wnt Proteins; D029961:Zebrafish Proteins; D051178:alpha Catenin; D002154:Calpain; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex