Investigation of signal transduction pathways involved in melanoma cell spreading

Integrins are a major family of heterodimeric adhesion receptors that are responsible for anchoring cells to extracellular matrix and they also can initiate intracellular signal pathways. Here parental and alpha 4-expressing human malignant melanoma cell lines were used to study the effect of protein kinase C (PKC), protein tyrosine kinases (PTKs) and intracellular Ca2+ on alpha 4 beta 1-mediated cell spreading on VCAM-1. Incubation of melanoma cells with PKC inhibitor inhibited alpha 4 beta 1-mediated melanoma cell spreading completely. Effect of intracellular Ca2+ on melanoma cell spreading was also investigated by non-phorbol ester tumor promotor, thapsigargin, which blocks the ability of the endoplasmic reticulum to replenish stocks of calcium which naturally leak out into the cytosol leading to a transient increase in concentration of intracellular calcium. The results showed that alpha 4 beta 1-mediated spreading was also required intracellular calcium involvement. However, in the presence of PTKs inhibitor melanoma cells showed long, thin dendiritic projections compared to control cells. Previously, data was obtained from immunofluorescense experiments showed that after genistein treatment, alpha 4-expressing cells exhibited considerable amounts of alpha 4 integrin and PTKs in both the focal contact points as well as over the whole cell. PTKs inhibitor did not have any effect on alpha 4-expressing cells spreading. This could be related to the amount of the PTKs present in these cells.