Stabilized beta-catenin immortalizes colonic epithelial cells

The majority of colonic neoplasias contain mutations in either the adenomat ous polyposis coli or the beta -catenin (beta -cat) gene, both of which res ult 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 tra nsforming cultured epithelial cells that represent the precursors to colon cancer. A truncated form of beta -cat (Delta N89) was stably expressed in m urine colonic epithelial cells that a ere conditionally immortalized by tem perature-sensitive T antigen expression and contained a mutant Apc(Min) all ele [Immorto-Min colonic epithelium (IMCE)]. IMCE cells, grown under nonper missive conditions, Here immortalized by expression of the truncated beta - cat protein as determined by sustained growth in culture and escape from se nescence as measured by endogenous beta -galactosidase activity. IMCE neo c ells at nonpermissive conditions underwent extensive apoptosis, an effect t hat was blocked by the expression of Delta N89 beta -catenin. IMCE beta -ca t cells bad 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 be ta -cat tells were also transformed as determined by growth in the absence of serum, anchorage-independent growth, and sustained tumor growth in nude mire. Stable beta -cat-expressing populations could not be generated in con ditionally immortalized colonic epithelial cells with a wild-type Apc backg round. 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.