Characterizing the invasion of different breast cancer cell lines with distinct E-cadherin status in 3D using a microfluidic system

E-cadherin is a cell-cell adhesion protein that plays a prominent role in cancer invasion. Inactivation of E-cadherin in breast cancer can arise from gene promoter hypermethylation or genetic mutation. Depending on their E-cadherin status, breast cancer cells adopt different morphologies with distinct invasion modes. The tumor microenvironment (TME) can also affect the cell morphology and invasion mode. In this paper, we used a previously developed microfluidic system to quantify the three-dimensional invasion of breast cancer cells with different E-cadherin status, namely MCF-7, CAMA-1 and MDA-MB-231 with wild type, mutated and promoter hypermethylated E-cadherin, respectively. The cells migrated into a stable and reproducible microfibrous polycaprolactone mesh in the chip under a programmed stable chemotactic gradient. We observed that the MDA-MB-231 cells invaded the most, as single cells. MCF-7 cells collectively invaded into the matrix more than CAMA-1 cells, maintaining their E-cadherin expression. The CAMA-1 cells exhibited multicellular multifocal infiltration into the matrix. These results are consistent with what is seen in vivo in the cancer biology literature. In addition, comparison between complete serum and serum gradient conditions showed that the MDA-MB-231 cells invaded more under the serum gradient after one day, however this behavior was inverted after 3 days. The results showcase that the microfluidic system can be used to quantitatively assess the invasion behavior of cancer cells with different E-cadherin expression, for a longer period than conventional invasion models. In the future, it can be used to quantitatively investigate effects of matrix structure and cell treatments on cancer invasion.

Mutant E-cadherin breast cancer cells do not display constitutive Wnt signaling

Participation of E-cadherin in the Wnt signaling pathway was suggested because of the dual role of beta-catenin in cell adhesion and the Wnt signaling cascade. Whereas beta-catenin interacts at the cell membrane with the cell adhesion protein E-cadherin, in the nucleus it activates Wnt target genes through formation of transcriptionally active complexes with members of the Tcf/Lef family of transcription factors. Here, we analyzed by PCR and direct cycle sequencing 26 human breast cancer cell lines for alterations in the E-cadherin gene. Genetic alterations were identified in eight cell lines. Five cell lines had truncating mutations, whereas three cell lines had in-frame deletions in the gene transcript and expressed mutant E-cadherin proteins at the cell membrane. Involvement of E-cadherin in the Wnt pathway was evaluated through determination of the activity of a Tcf reporter gene, which had been transiently transfected into 15 breast cancer cell lines. None of six E-cadherin mutant cell lines and four cell lines that exhibit transcriptional silencing of the E-cadherin gene showed Tcf-mediated transcriptional activation. E-cadherin wild-type cell line DU4475 exhibited constitutive Tcf-beta-catenin signaling activity and was found to express truncated APC proteins. These results indicate that if cellular transformation occurred through mutation of E-cadherin, it is not mediated via constitutive activation of the Wnt signaling pathway.