E-cadherin impairment increases cell survival through Notch-dependent upregulation of Bcl-2

The role of E-cadherin in tumorigenesis has been attributed to its ability to suppress invasion and metastization. However, E-cadherin impairment may have a wider impact on tumour development. We have previously shown that overexpression of mutant human E-cadherin in Drosophila produces a phenotype characteristic of downregulated Notch. Hence, we hypothesized that Notch signalling may be influenced by E-cadherin and may mediate tumour development associated with E-cadherin deficiency. De novo expression of wild-type E-cadherin in two cellular models led to a significant decrease in the activity of the Notch pathway. In contrast, the ability to inhibit Notch-1 signalling was lost in cells transfected with mutant forms of E-cadherin. Increased Notch-1 activity in E-cadherin-deficient cells correlated with increased expression of Bcl-2, and increased resistance to apoptotic stimuli. After Notch-1 inhibition, E-cadherin-deficient cells were re-sensitized to apoptosis in a similar degree to wild-type E-cadherin cells. We also show that Notch-inhibiting drugs are able to significantly inhibit the growth of E-cadherin-deficient cells xenografted into nude mice. This effect was comparable with the one observed in animals treated with the chemotherapeutic agent taxol, a chemical inducer of cell death. In conclusion, our results show that aberrant Notch-1 activation, Bcl-2 overexpression and increased cell survival are likely to play a crucial role in neoplastic transformation associated with E-cadherin impairment. These findings highlight the possibility of new targeted therapeutical strategies for the treatment of tumours associated with E-cadherin inactivation.