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Our studies were focused on the isolation and characterization of highly motile fraction of cells from hepatoma Morris 5123 population. Cells that underwent several migration cycles through Matrigel - coated filters were successfully cultured. The invasion index was determined by means of Matrigel invasion assay. Statically significant increase in the value of invasion factor for selected cells variant in comparison to the parental population was observed. The considerable changes in the cell shape were followed by the reorganization of the actin cytoskeleton structure including a dense subcortical congestion in the distribution of ß-actin isoform. The visualization of this protein in tumor cells was performed by immunostaining and scanning fluorescent confocal microscopy. The results were confirmed by densitometry analysis of Western blots. In addition, the increased state of actin polymerization in the cytoplasmic fraction of selected cells was determined as measured by filamentous to monomeric (F:G) actin ratio. Concluding, the selected fraction of hepatoma Morris 5123 cells with higher invasion capacity was characterized by rounded shape, remarkable increase of ß-actin level, its submembrane concentration as well as with the increased state of actin polymerization with respect to parental cells population.
Human colon adenocarcinoma LS180 parental cell line and selected variants, characterized by different metastatic capacity were used to examine, whether a correlation exists between β-actin expression, its subcellular distribution and metastatic potential of these cells. Cytosolic fraction (supernatant 105 000 × g), isolated from the tumor cells was used as a source for actin quantification. The higher level of β-actin was observed in the cytosol of three selected sublines to compare with LS180 parental line. Statistically significant increase of β-actin level in highly motile EB3 cells variant should be underlined to compare with the other sublines. Distinct differences in the phenotype of adenocarcinoma cell variants were found, such as the changes in cells shape, cells spreading and ability to attach to the surface of culture dish. Actin cytoskeleton was visualized with fluorescence microscopy application and microfilaments rhodamine-conjugated phalloidin staining. β-actin subcellular localization was done by immunofluorescence staining with monoclonal anti-β actin antibodies. In the elongated cells (LS180, 3LNLN), this isoactin is dispersed in the whole cell body and concentrates in pseudopods and at the leading edges, when in the rounded variant (EB3) β-actin dominates mainly in cortical ring under cellular membrane and it is also seen in the subtle protrusions. Summary of our former (Nowak et al., 2002, Acta Biochim. Polon., 49: 823) and current data lead to the conclusion that there is a distinct correlation between metastatic capacity of examined human colon adenocarcinoma cells, the state of actin polymerization, actin cytoskeleton organization and β-actin expression.
Monomeric (G), total (T) and filamentous (F) actin and the state of actin polymerisa­tion (F:G) were determined and actin filaments were visualized in hepatoma Morris 5123 cells cultured in the presence of methotrexate (MTX) at various concentration. The exposure of the cells to this drug resulted in a decrease of total and polymerised actin in cytoplasm and in some changes in actin filament organization. This coincided with a decrease of the cells' ability to migrate through Matrigel coated filters and with inhibition of tumour formation after reimplantation of the methotrexate treated cells to experimental rats.
The hepatoma Morris 5123 tumor growth is accompanied by changes in actin content and polymerization (Malicka-Błaszkiewicz et al. (1995) Mat. Med. Pol., 27, 115-118; Nowak et al. (1995) J. Exp. Cancer Res. 14, 37-40). Presently actin isoforms from cytosol and cytoskeleton fractions were separated by SDS/PAGE and identified with antibodies directed against different actin isoforms. Actin isolated from the cytosol by affinity chromatography on DNase I bound to agarose shows the presence of only one protein spot on 2D gel electrophoresis corresponding to the mobility of the rabbit α skeletal muscle actin (Mr 43000) and isoelectric point equal to 5.3. It interacts only with monoclonal anti β actin isoform antibodies, posing the question of differential affinity of actin isoforms to DNase I.
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