Thrombin stimulates arachidonate metabolism in murine tumor cells

Effect of different platelet agonists on intracellular free Ca++ concentrations in human tumor cells: possible role in tumor growth

Modulation of cytoplasmic Ca++ concentration is a mechanism common to signal transduction pathways regulating many cellular phenomena, including the interactions of tumors with the hemostatic system. We have investigated the pro-aggregating and pro-coagulant activities of human tumor cell lines cultured in vitro and the ability of different platelet agonists to induce Ca++ transients in these cells. Cells of a malignant mesothelioma line activated platelets by a thrombin-dependent mechanism; on the contrary, HeLa cells, derived from a uterine cervical cancer, possessed ADP-dependent pro-aggregating activity, and DND-IA melanoma cells did not stimulate platelet aggregation. All cell lines showed a tissue-factor-like procoagulant property, more pronounced in mesothelioma cells. Furthermore, ADP was able to induce a transient increase in cytoplasmic Ca++ concentration in tumor cells from all lines; collagen showed this effect in mesothelioma cells and in HeLa cells, and thrombin was effective only in mesothelioma cells. PAF never induced Ca++ fluxes in any of the cell lines investigated. Finally, the calcium-channel blocker verapamil inhibited agonist-induced Ca++ transients in tumor cells and in vitro tumor-cell growth. These data may help to identify new possible mechanisms of the 2-way interaction of tumors with the hemostatic system.

Simultaneous production of IGF-I and EGF competing growth factors by HT-29 human colon cancer line

The conditioned medium from the HT-29 human colonic adenocarcinoma cell line contains a potent mitogenic activity that can markedly stimulate the proliferation of both rat and human fibroblasts in the absence of serum. Fractionation of conditioned medium on Bio-Gel P-100 shows that HT-29 cells simultaneously produce 2 different types of endogenous growth factors. The first one (molecular mass of 35, 8 and 5.5 kDa) exhibits an IGF-I competing activity which is positively correlated to mitogenic activity. This mitogen is recognized by anti-IGF-I antibodies but is resistant to reducing agents. It is distinct from IGF-II, insulin and PDGF. The second one (molecular mass of 40- and 20-kDa) is able to displace EGF binding to its receptor. This factor is immunologically recognized by anti-EGF antibodies but with a lower affinity as compared to EGF. This suggests that this endogenous HT-29-growth factor is related to but distinct from native EGF. Although more active in radioreceptor assay than in radioimmunoassay, the EGF-competing factor is distinct from TGF alpha or beta since it is unable to induce anchorage-independent growth of NRK or FR3T3 target cells in the presence or absence of exogenous EGF. Moreover, free functional EGF receptors are available at the HT-29 cell surface.