Stabilized beta-catenin immortalizes colonic epithelial cells.
The majority of colonic neoplasias contain mutations in either the adenomatous polyposis coli or the beta-catenin (beta-cat) gene, both of which result in elevated levels of cytoplasmic beta-cat. The oncogenic activity of beta-cat has been explored in vivo and in vitro with conflicting results. We tested the hypothesis that beta-cat is capable of immortalizing and transforming cultured epithelial cells that represent the precursors to colon cancer. A truncated form of beta-cat (deltaN89) was stably expressed in murine colonic epithelial cells that were conditionally immortalized by temperature-sensitive T antigen expression and contained a mutant ApcMin allele [Immorto-Min colonic epithelium (IMCE)]. IMCE cells, grown under nonpermissive conditions, were immortalized by expression of the truncated beta-cat protein as determined by sustained growth in culture and escape from senescence as measured by endogenous beta-galactosidase activity. IMCE neo cells at nonpermissive conditions underwent extensive apoptosis, an effect that was blocked by the expression of deltaN89 beta-catenin. IMCE beta-cat cells had significantly lower p19 and p53 protein levels compared to IMCE neo cells, suggesting that alterations in these two key genes may mediate the effects of beta-cat on both cellular senescence and apoptosis. IMCE beta-cat cells were also transformed as determined by growth in the absence of serum, anchorage-independent growth, and sustained tumor growth in nude mice. Stable beta-cat-expressing populations could not be generated in conditionally immortalized colonic epithelia cells with a wild-type Apc background. These studies demonstrated the immortalizing activity of stabilized beta-cat for the first time and extend the transforming ability of mutated beta-cat to a cell line representing a precursor to colorectal cancer.
Wagenaar
R A
RA
Department of Cancer Biology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
Crawford
H C
HC
Matrisian
L M
LM
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D002461:Cell Line, Transformed; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000473:pathology*; D003106:Colon / Q000166:cytology* / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D005260:Female; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D014176:Protein Biosynthesis; D015534:Trans-Activators; D025803:Tumor Suppressor Protein p14ARF; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis; D051176:beta Catenin
C495267:CTNNB1 protein, mouse; D003598:Cytoskeletal Proteins; D015534:Trans-Activators; D025803:Tumor Suppressor Protein p14ARF; D016159:Tumor Suppressor Protein p53; D051176:beta Catenin