Relationship between tumor cell invasiveness and polyploidization.

A number of studies have shown that tumor cells fuse with other tumor and non-tumor cells. In the present study on tumor cell lines derived from glioblastoma, breast cancer, and melanoma, we estimated the frequency of fusion between tumor cells by establishing the fraction of cells with whole tumor-genome duplication in each cell line. Together with this, the capacity of the tumor cell lines to spread through a basement membrane scaffold was assessed, in order to test the hypothesis that pericellular proteolysis by enzymatic release in the spaces of intercellular contact could account for differences in the fusogenicity of tumor cells. The difference in invasiveness between the cell lines accounted for their specific amount of cells with tumor-genome duplication, which, depending on the cell line analyzed, ranged from 2% to 25% of the total cells. These results support the hypothesis that cell-to-cell invasion eliciting membrane fusion causes polyploidization in tumor cells

Relationship between invasiveness and polyploidization in tumor cells.

<p>Graph displaying a proportional ratio (r²>0.95) between the level of polyploidization in the tumor cell lines U87MG, FEMX-I, MDA-MB-231, and MA11, as expressed by the value of the gradient of the regression line, and average density of tumor cell invasion through matrigel.</p

Detection in human tumor cell lines of cells containing four-fold DNA amount.

<p>Flow cytometric analysis of cultures of the tumor lines U87MG, FEMX-I, MDA-MB-231, and MA11, at either low (top panels) or high (bottom panels) rate of proliferation, showing the distribution of cells according to DNA content, expressed as intensity of red fluorescence, and forward scatter (arbitrary units); the bar graph on top of each panel shows the percentage of cells in the G0/G1 peak (lowest DNA amount per cell), and that of cells with 2- (including cells in S phase), and 4-fold the intensity of the cells of the G0/G1 peak. The average fluorescence of each of the three populations is indicated by arrowheads. In all the cell lines, a greater number of cells with four-fold DNA quantity is present in the rapidly proliferating culture, representing 3%, 2%, 12%, and 1% of the total cells for U87MG, FEMX-I, MDA-MB-231, and MA11, respectively.</p

Relationship between cell proliferation in culture and number of tumor cells containing four-fold DNA amount.

<p>(A) Inverse relationship (r²>0.95) in U87MG, FEMX-I, MDA-MB-231, and MA11 cell lines, between the number of cells in the G0/G1 peak and that of cells carrying four-fold DNA amount, as quantitated in cultures of each cell line by flow cytometric analysis for content of DNA; both cell populations are expressed as fractions over the total number of cells analysed from each culture. (B) Lack of correlation in cultures of fibroblasts (top panel), <i>vs.</i> negative correlation in cultures of U87MG glioma cells (bottom panel), between number of cells in the G0/G1 peak and number of cells carrying four-fold DNA amount.</p

Matrigel invasion by U87MG, FEMX-I, MDA-MB-231, and MA11 tumor cell lines.

<p>Fluorescence microphotographs of representative areas of the underside of matrigel-coated membranes in transwell assays, showing that U87MG and MDA-MB-231 invade more efficiently through the matrigel, roughly by 4- and 7-fold, respectively, than MA11 and FEMX-I. The cells were fluorescently labeled with 4′,6-diamidino-2-phenylindole, appearing dark in the inverted images. Bars, 100 µm.</p