Functional cross-talk of Ca2+-mobilizing endothelin receptors in C6 glioma cells.

There are conflicting results concerning the receptor subtype(s) involved in calcium-mediated endothelin signaling in the glial cells. In order to elucidate the role of endothelin A and B receptors in these processes, we have studied the effect of a complex spectrum of endothelin receptor ligands on intracellular calcium concentration changes in proliferating and differentiated C6 rat glioma cells. Cell differentiation was induced by dibutyryl-cAMP and assessed by the glial fibrillar acidic protein content. Intracellular calcium changes were measured in cell suspensions using fluorescent probe Fura-2. The specific endothelin B receptor agonists sarafotoxin S6c and IRL-1620 did not influence the intracellular calcium concentration. However, calcium changes induced by endothelin-1 and especially by endothelin-3 after the pretreatment of cells with one of these endothelin B receptor specific agonists were significantly enhanced even above the values attained by the highest effective endothelin concentrations alone. Such endothelin B-receptor ligand-induced sensitization of calcium signaling was not observed in differentiated C6 cells. Moreover, endothelin-induced calcium oscillations in differentiated C6 cells were less inhibited by BQ-123 and BQ-788 than in their proliferating counterparts. In conclusion, the specific activation of endothelin B receptor in C6 rat glioma cells does not affect intracellular calcium per se, but probably does so through interaction with the endothelin A receptor. The pattern and/or functional parameters of endothelin receptors in C6 rat glioma cells are modified by cell differentiation.

Dipeptidyl peptidase IV in two human glioma cell lines.

There is growing evidence that dipeptidyl peptidase IV [DPP-IV, EC 3.4.14.5] takes part in the metabolism of biologically active peptides participating in the regulation of growth and transformation of glial cells. However, the knowledge on the DPP-IV expression in human glial and glioma cells is still very limited. In this study, using histochemical and biochemical techniques, the DPP-IV activity was demonstrated in two commercially available human glioma cell lines of different transformation degree, as represented by U373 astrocytoma (Grade III) and U87 glioblastoma multiforme (Grade IV) lines. Higher total activity of the enzyme, as well as its preferential localisation in the plasma membrane, was observed in U87 cells. Compared to U373 population, U87 cells were morphologically more pleiomorphic, they were cycling at lower rate and expressing less Glial Fibrillary Acidic Protein. The data revealed positive correlation between the degree of transformation of cells and activity of DPP-IV. Great difference in expression of this enzyme, together with the phenotypic differences of cells, makes these lines a suitable standard model for further studies of function of this enzyme in human glioma cells.

Expression of attractin and its differential enzyme activity in glioma cells.

Attractin/mahogany protein was previously shown to be involved in a number of physiological and pathological events, including immune system regulation, body weight control, pigmentation, myelinization, and tumor susceptibility. Human attractin has an enzymatic activity resembling dipeptidyl peptidase IV (DPP-IV). In the central nervous system, attractin has been detected in neurons but not in glial cells up to now. We show the expression of attractin mRNA and protein in glioma cell lines at different degree of transformation. In human U373 and U87 glioma cells (Grades III and IV), membrane-bound attractin displays hydrolytic activity amounting to 5 and 25% of total cellular DPP-IV-like enzyme activity, respectively. Such activity has not been observed in the rat C6 glioma cells (Grade I). Attractin presence in glioma, but not in normal glial cells, together with its differential enzymatic activity, suggests its role in growth properties of tumors of glial cell origin.

Calcium-mediated endothelin signaling in C6 rat glioma cells.

Endothelin induced intracellular Ca(2+)signaling was studied in C6 rat glial cells. Endothelins 1 and 3 increased transiently intracellular Ca(2+)concentration, endothelin 3 being less potent inducer. Dibutyryl-cAMP treated cells responded with less sensitivity. While BQ123, a specific endothelin A receptor antagonist, inhibited both endothelins induced response in proliferating cells, it failed to inhibit in dibutyryl-cAMP treated ones. IRL1620, a specific endothelin B receptor agonist, was devoid of any significant effect. Although re-stimulation by both endothelins after endothelin-1 did not cause any Ca(2+)oscillation, both endothelins evoked new Ca(2+)transient after endothelin-3 stimulation. Our findings suggest that endothelin induced Ca(2+)signaling is mediated probably through the receptor A in proliferating C6 cells. The lack of both BQ123 and IRL 1620 effect in dibutyryl-cAMP treated cells could be caused by an alteration of endothelin A receptor alone, by a change of receptor expression pattern, or by more complex postreceptor mechanism.

[Plasma and tissue levels of cytokines and adhesive molecules in patients before strumectomy]. / Plazmatické a tkánové koncentrace cytokinu a adhezivních molekul u pacientu pred strumektomií.

From a group of 134 patients with complete documentation before goitrectomy the authors selected 10 histologically defined cases of (A) simple colloid nodular goitre, (B) toxic parenchymatous goitre type GB and (C) autoimmune thyroiditis. Marked hormonal suppression was achieved in group B by thyrostatic therapy, as compared with A and C, the autoantibody titres (TGAb and TMAb) differentiated the groups. The authors examined the interleukin 6 concentrations and those of its soluble receptor (IL-6, IL-6R), of the tumour necrotizing factor alpha (TNF-alpha) interferon gamma (IFN-gamma) and of adhesion molecules ICAM-1 and VCAM-1. Plasma values were, except for not very significant differences, similar in all groups and ruled out a marked effect on tissue levels. The most remarkable finding in the homogenate of a peroperative excision were low IL-6, IL-6R and adhesion molecule values in group A, as compared with B and C and the absence of differences in TNF-alpha values between groups and in particular markedly higher IFN-gamma values in group B which supports theories on the etiopathogenetic role of this cytokine in GB disease. The pilot study is part of the preparation of in situ hybridization of mRNA for diagnostically usable cytokines.