A dynamic in vivo model of epithelial-to-mesenchymal transitions in circulating tumor cells and metastases of breast cancer.

Epithelial-to-mesenchymal transition (EMT) processes endow epithelial cells with enhanced migratory/invasive properties and are therefore likely to contribute to tumor invasion and metastatic spread. Because of the difficulty in following EMT processes in human tumors, we have developed and characterized an animal model with transplantable human breast tumor cells (MDA-MB-468) uniquely showing spontaneous EMT events to occur. Using vimentin as a marker of EMT, heterogeneity was revealed in the primary MDA-MB-468 xenografts with vimentin-negative and vimentin-positive areas, as also observed on clinical human invasive breast tumor specimens. Reverse transcriptase-PCR after microdissection of these populations from the xenografts revealed EMT traits in the vimentin-positive zones characterized by enhanced 'mesenchymal gene' expression (Snail, Slug and fibroblast-specific protein-1) and diminished expression of epithelial molecules (E-cadherin, ZO-3 and JAM-A). Circulating tumor cells (CTCs) were detected in the blood as soon as 8 days after s.c. injection, and lung metastases developed in all animals injected as examined by in vivo imaging analyses and histology. High levels of vimentin RNA were detected in CTCs by reverse transcriptase-quantitative PCR as well as, to a lesser extent, Snail and Slug RNA. Von Willebrand Factor/vimentin double immunostainings further showed that tumor cells in vascular tumoral emboli all expressed vimentin. Tumoral emboli in the lungs also expressed vimentin whereas macrometastases displayed heterogenous vimentin expression, as seen in the primary xenografts. In conclusion, our data uniquely demonstrate in an in vivo context that EMT occurs in the primary tumors, and associates with an enhanced ability to intravasate and generate CTCs. They further suggest that mesenchymal-to-epithelial phenomena occur in secondary organs, facilitating the metastatic growth.

Fhit regulates invasion of lung tumor cells.

In many types of cancers, the fragile histidine triad (Fhit) gene is frequently targeted by genomic alterations leading to a decrease or loss of gene and protein expression. Fhit has been described as a tumor suppressor gene because of its ability to induce apoptosis and to inhibit proliferation of tumor cells. Moreover, several studies have shown a correlation between the lack of Fhit expression and tumor aggressiveness, thus suggesting that Fhit could be involved in tumor progression. In this study, we explored the potential role of Fhit during tumor cell invasion. We first showed that a low Fhit expression is associated with in vivo and in vitro invasiveness of tumor cells. Then, we showed that Fhit overexpression in Fhit-negative highly invasive NCI-H1299 cells by transfection of Fhit cDNA and Fhit inhibition in Fhit-positive poorly invasive HBE4-E6/E7 cells by transfection of Fhit small interfering RNA induce, respectively, a decrease and an increase in migratory/invasive capacities. These changes in cell behavior were associated with a reorganization of tight and adherens junction molecules and a regulation of matrix metalloproteinase and vimentin expression. These results show that Fhit controls the invasive phenotype of lung tumor cells by regulating the expression of genes associated with epithelial-mesenchymal transition.

The E-cadherin-repressed hNanos1 gene induces tumor cell invasion by upregulating MT1-MMP expression.

In this study, we examined the role of the E-cadherin-repressed gene human Nanos1 (hNanos1) in tumor invasion process. First, our in vivo study revealed that hNanos1 mRNAs were overexpressed in invasive lung carcinomas. Moreover, hNanos1 was co-localized with MT1-MMP (membrane type 1-matrix metalloproteinase) in E-cadherin-negative invasive lung tumor clusters. Using an inducible Tet-on system, we showed that induction of hNanos1 expression in DLD1 cells increased their migratory and invasive abilities in a three-dimensional migration and in a modified Boyden chamber assay. Accordingly, we demonstrated that hNanos1 upregulated MT1-MMP expression at the mRNA and protein levels. Inversely, using an RNA interference strategy to inhibit hNanos1 expression in invasive Hs578T, BT549 and BZR cancer cells, we observed a downregulation of MT1-MMP mRNA and protein and concomitantly a decrease of the invasive capacities of tumor cells in a modified Boyden chamber assay. Taken together, our results demonstrate that hNanos1, by regulating MT1-MMP expression, plays an important role in the acquisition of invasive properties by epithelial tumor cells.