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.

Actividad tirosina-protein-quinasas en cáncer de mama: correlación con algunos elementos de pronóstico / Tyrosine-protein-kinase activity in breast cancer: correlation with some pronostic elements

Diversas evidencias acumuladas en los últimos años relacionan la actividad de tirosina-protein-quinasa (TPK) con la transformación celular maligna y permiten suponer una relación entre dicha actividad y la capacidad de proliferación tumoral y por lo tanto, el pronóstico. En este trabajo se relaciona la actividad de TPK en 27 biopsias obtenidas de cáncer mamario humano con diversos parámetros clínicos y anátomo-patológicos de pronóstico. Las muestras de tejido fueron obtenidas quirúrgicamente de pacientes que presentaban cáncer de mama demostrado. Se determinó la actividad TPK en homogeneizados de tejido mamario utilizando (Val5) angiotensina II como sustrato exógeno. El estudio demostró una relación estadística entre la actividad global real de TPK (actividad TPK de las células tumorales menos la actividad TPK de las células mamarias normales) y el tamaño clínico del tumor, así como con el ² termográfico, sin encontrar relación con el número de ganglios invadidos ni con la pobre diferenciación celular. Estos antecedentes hacen suponer que de existir una relación entre la actividad global real de TPK y la evolución tumoral, ésta sea más bien con la velocidad de crecimiento que con el potencial metastizador

Phosphorylation of ribosomal protein S6 and its regulation during differentiation of human leukemic cells

We attempted to study the role of protein tyrosine kinase (PTK) and protein kinase C (PKC) in the cascade of phosphorylation of ribosomal protein S6 during differentiation of leukemic cells (HL-60, THP-1, and RWLeu-4). Neither activation nor inhibition of colony stimulating factor-1 (CSF-1) receptor's PTK activity with CSF-1 or genistein respectively affected the phosphorylation of S6. However, vanadate which is a protein tyrosine phosphatase (PTP) inhibitor showed enhancement of S6 phosphorylation. Dimethylsulfoxide which does not affect either PTK or PKC demonstrated no change in S6 phosphorylation. PKC activation by acute 12-0-tetradecanoyl phorbol-13-acetate (TPA) treatment induced monocytic differentiation and S6 phosphorylation. Surprisingly, the more prominent phosphorylation of S6 protein was observed in PKC-depleted cells by prolonged TPA treatment. Our results suggest that PTK/PTP play a lesser role in S6 phosphorylation of HL-60 cells than PKC does. In addition, two different mechanisms seem to be involved in TPA-induced S6 phosphorylation during HL-60 differentiation: PKC activation by acute TPA treatment and PKC depletion which may lead to the synthesis of some endogenous protein responsible for the differentiation by chronic TPA treatment.