Effects of gadolinium ions upon rat prostatic cancer cell lines of markedly different metastatic potential

Voltage-sensitive ion channels and cancer

Plasma membrane voltage-sensitive ion channels classically have been associated with a variety of inherited diseases or "channelopathies" that range in the severity of symptoms from mild to lethal. Ion channels are found throughout the body and are responsible for facilitated diffusion of ions down the electrochemical gradient across cells membranes in various tissues. Voltage-sensitive ion channels open in response to changes in the membrane potential and are primarily found in excitable cells and tissues. Potassium, calcium, and sodium channels play critical roles in the development of major diseases, such as hyperkalemia, epilepsy, congenital myotonia and several cardiac arrythmias. Recently, cancer studies have begun to define the role of voltage-sensitive ion channels in the progression of cancer to a more malignant phenotype. In cancer, the increased expression or increased kinetics of voltage-sensitive ion channels is associated with an increasing malignant potential as evinced by their role in cell proliferation, migration and survival; as such, these channels are becoming the targets of significant drug development efforts to block or reduce voltage-sensitive ion channel activity in order to prevent or combat malignant disease.

An inhibitor of the stretch-activated cation receptor exerts a potent effect on chondrocyte phenotype

Rat chondrosarcoma (RCS) cells are unusual in that they display a stable chondrocyte phenotype in monolayer culture. This phenotype is reflected by a rounded cellular morphology with few actin-containing stress fibers and production of an extracellular matrix rich in sulfated proteoglycans, with high-level expression of aggrecan, COMP, Sox9, and collagens type II, IX, and XI. Additionally, these cells do not express collagen type I. Here it is shown that in the absence of any mechanical stimulation, treatment of RCS cells with gadolinium chloride (Gd3+), a stretch-activated cation channel blocker, caused the cells to undergo de-differentiation, adopting a flattened fibroblast phenotype with the marked appearance of actin stress fibers and vinculin-containing focal contacts. This change was accompanied by a dramatic reduction in the expression of aggrecan, Sox9, collagen types II, IX, and XI, with a corresponding increase in the expression of collagen type I and fibronectin. These effects were found to be reversible by simple removal of Gd3+ from the medium. Gd3+ also had a similar effect on expression of chondrocyte marker genes in freshly isolated human chondrocytes. These data suggest that mechanoreceptor signaling plays a key role in maintenance of the chondrocyte phenotype, even in the absence of mechanical stimulation. Further, treatment of RCS cells with Gd3+ provides a tractable system for assessing the molecular events underlying the reversible differentiation of chondrocytes.

Homotypic cell-cell contacts stimulate the motile activity of rat prostate cancer cells

OBJECTIVE

To characterize the effect of homotypic cell-to-cell collisions upon the motile activities of two rat prostatic cancer cell lines of markedly different metastatic potential.

MATERIALS AND METHODS

The movements of strongly and weakly metastatic MAT-LyLu and AT-2 cells, respectively, were recorded under an inverted microscope at 37 degrees C. The motile activities of the cells at various cell densities were characterized quantitatively by computer-aided tracking methods and image analysis. The following variables were assessed: speed of movement, final displacement, coefficient of movement efficiency, diffusion constant and positive flow.

RESULTS

MAT-LyLu and AT-2 cells showed only limited motile activity in sparse cultures where there was little contact amongst the cells. However, under these and all other subsequent conditions tested, the motile activity of the MAT-LyLu cells was higher than the AT-2 cells. As the density of the cultured cells was increased (leading to more cell-to-cell contacts) there was a significant increase in motility. This effect was more pronounced for the AT-2 than for the MAT-LyLu cells, resulting in visible acceleration of movement by direct physical contact among the colliding cells. The motile activities of the tumour cells was only slightly affected by conditioned media.

CONCLUSION

Homotypic collisions between migrating prostatic cancer cells can strongly stimulate their motility. The effect of increased contact is greater on the weakly metastatic cells, such that at high cell density, the difference in the motilities of weak and strong metastatic cells is greatly reduced.

Contact-activated migration of melanoma B16 and sarcoma XC cells

During migration, tumour cells interact with neighbouring neoplastic and normal host cells, and such interaction may influence their motile activity. We investigated the effect of homotypic collisions on the motile activity of two tumour cell lines, mouse melanoma B16 and rat sarcoma XC, and nontransformed human skin fibroblasts. It was found that the tumour cells show only limited motile activity when moving as single cells without contact with neighbours. At a higher density of the culture (and also at a greater number of cell to cell contacts) the activation of motility of investigated tumour cells was observed. On the other hand, the normal human skin fibroblasts showed a typical reaction of density-dependent inhibition of motility. The motile activity of tumour cells was not affected by conditioned media and was visibly dependent on a direct physical contact among colliding cells. The activation of cell movement was observed about 40–50 min after the initial contact between tumour cells. Contact-activated migration of neoplastic cells was inhibited by 50 µM verapamil (a selective voltage-gated calcium channel inhibitor) and 10 µM gadolinium chloride (a nonspecific blocker of mechanosensitive ion channels) but not by pertussis toxin. The observation that homotypic collisions among tumour cells strongly increase their motile activity suggests that contact-activated migration may play a significant role in tumour invasion and metastasis.Key words: cell movement, metastases, contact activation of cell migration, contact inhibition.