gms | German Medical Science

Objective: Cadherins are key components of the adherens junction complexes. Thus, they are responsible for cell-cell adhesion as well as cell motility. Especially in epithelial carcinomas, loss of E-cadherin contributes to diminished cell polarity and promotes epithelial-mesenchymal transition (EMT). This alteration frequently leads to a more invasive phenotype which is accompanied with a worse prognosis for patients. Interestingly, some studies revealed expression of E-cadherin in a rare subset of GBM cells which was correlated with a more unfavorable clinical outcome.

Method: During investigation of cadherin expression levels in different tumor glial cell lines and primary cultures we found one low-invasive cell line that expressed E-cadherin. Subcellular protein localization as well as RNA level of wild type U343-MG was compared to E-cadherin level in epithelial breast cancer cell line MCF-7. For functional analysis retroviral transduction with two shRNA-vectors was used to stably knockdown (KD) E-cadherin in both cell lines. The resulting phenotype was analyzed by western blot, BrdU (5-bromo-2'-deoxyuridine)-incorporation, clonogenic survival assay, and apoptosis assay. To determine tumorigenic potential and invasion capacity wound healing assay, boyden chamber assay, and spheroid formation experiments were performed.

Results: Our findings indicate that similar to MCF-7 control cells E-cadherin is mainly localized to the cell membrane in U343-MG glioma cells beside differences in the propeptide RNA sequence. Both generated shRNAs could significantly downregulate E-cadherin protein level. Following KD of E-cadherin, U343-MG cells lost their cell-cell contact and shifted from a cobblestone-like to a mesenchymal phenotype, even if N-cadherin level was not upregulated. In summary, U343-MG KD cells showed significantly higher apoptosis rates, decreased proliferation, and clonogenic survival and were unable to build neurospheres. In wound healing and boyden chamber assay E-cadherin depleted U343-MG displayed differential results concerning their migration and invasion potential, dependent on applied individual shRNAs.

Conclusions: Unlike the classical GBM phenotype, E-cadherin depleted U343-MG cells did not show a carcinogenic EMT that is normally accompanied with a more aggressive tumor. Our findings suggest a critical role of E-cadherin in migration and survival in a small subset of GBM.