Phenotypic effect of two human tongue cancer cell lines in tumorigenesis

Abstract

Epithelial to mesenchymal transition (EMT) is a cellular programme in which a cell turns from a differentiated, epithelial state (E-state) into a mesenchymal state (M-state). Epithelial cells that undergo EMT lose cell to cell adhesion, increase their motile ability and become invasive. EMT is widely involved in physiological embryonic development, wound healing as well as in pathologic organ fibrosis and cancer progression. Although the biological process and molecular mechanisms of EMT have been intensively studied in vitro, the animal model to investigate the phenotypic effect of the cancer cells in tumor growth and progression remains lacking. The here presented study aimed to

1) Label two human oral cancer cell lines, one in an epithelial, the other one in a mesenchymal state, with different fluorescence expressing proteins

2) Establish a novel animal model where cell lines in epithelial and mesenchymal state can be visualized due to different fluorescence

3) Study cancer progression of oral cancer cell lines with epithelial and mesenchymal phenotype in cancer progression after subcutaneous and intravenous injection.

Via lentiviral particle transduction green fluorescent protein (GFP) and red fluorescent protein (RFP) were transduced into the host cell’s genome of two human cancer cell lines, UM1 (M-state) and UM2 (E-state) respectively. Over several generations the transduced cells UM1-GFP and UM2-RFP could stably express fluorescent proteins, being easily visualizable under fluorescent microscopy. UM1-GFP and UM2-RFP both presented stable fluorescent signals over a long term period, assessed by under the microscope and with flow cytometry.

Lentiviral transduction of GFP and RFP might influence or even change the phenotypic state of the cancer cell lines, a fact which was still unknown. This in vitro study discovered that the phenotypic states of UM1-GFP and UM2-RFP remained the same after transduction.

A nude mouse model was established to study the tumorigenicity and the possibility to visualize the transduced cancer cell lines UM1-GFP and UM2-RFP. A similar tumorigenicity, in terms of tumor take rate and tumor volume between the parental and transduced cancer cell lines could be confirmed. Fluorescent visualization could be demonstrated both in in vivo and ex vivo imaging of harvested organs.

Hypothetically rodent cancer cells of epithelial and mesenchymal phenotype were supposed to cooperate with each other in the establishment of lung metastasis after subcutaneous injection. This study used two human oral cancer cell lines of epithelial and mesenchymal phenotype to test this particular hypothesis. Subcutaneous inoculation of both human oral cancer cell lines was unable to form spontaneous metastasis in naked, immunocompromised mice. Only the epithelial phenotype cancer cell line was able to create lung cancer when injected into the tail vein.