✓ The authors have previously shown that meningioma-derived conditioned medium profoundly stimulates the in vitro proliferation of meningioma cells. In this paper, self-mitogenic agents found in the conditioned medium—autocrine growth-stimulatory factors actually secreted by human meningioma cells—are characterized as proteins related to the B chain of platelet-derived growth factor (PDGF) and possibly to the A chain of PDGF as well. The addition to conditioned medium of a neutralizing antibody against PDGF-BB caused a significant inhibition of the conditioned medium—stimulated DNA synthesis in all three meningioma cultures studied. A similar neutralizing effect was observed with an anti—PDGF-AA antibody in one meningioma culture studied. Gel filtration chromatography of concentrated conditioned medium from two different meningiomas using a Sephadex G-100 column revealed similar profiles from both conditioned media with a major peak of mitogenic activity against meningioma cells at a molecular weight (Mr) of approximately 32 to 36 kD, accompanied by a minor peak at approximately 22 kD. The major peak mitogenic activity was significantly reduced by addition of an anti—PDGF-BB antibody. Western blot analysis of protein extracts from five meningioma specimens was performed using a monoclonal antibody against the B chain of PDGF, and a major band of PDGF-B immunoreactivity was detected at an Mr of approximately 19 kD in all five meningiomas under both reducing and nonreducing conditions. Exogenous human and porcine PDGFs both exhibited a significant dose-dependent stimulation of DNA synthesis in two of three and three of five meningioma cultures examined, respectively. Although not all meningiomas investigated proved to share the biological activity associated with PDGF and these results may be preliminary, it seems that the autocrine growth-stimulatory loop established by PDGF-B—related molecules plays an important functional role in meningioma cell proliferation.
Tomoki Todo, Eric F. Adams, Rudolf Fahlbusch, Theodor Dingermann and Herbert Werner
Tomoki Todo, Eric F. Adams, Brian Rafferty, Rudolf Fahlbusch, Theodor Dingermann and Herbert Werner
✓ Using cell culture techniques, the authors have previously shown that human meningioma cells secrete an autocrine growth stimulator related to platelet-derived growth factor. Here, they further demonstrate potential autocrine inhibitory regulation of meningioma cell growth by interleukin (IL)-6. Constitutive IL-6 production was detected in all meningiomas studied, in the form of protein as well as IL-6-specific messenger ribonucleic acid. The IL-6 immunoreactivity in conditioned medium from three different meningioma cultures eluted from a Sephadex G-100 column was evidenced by a single peak corresponding to a molecular weight of about 32 kD. Interleukin-6 secretion was remarkably stimulated by tumor necrosis factor-α, IL-1β, and IL-4, and was also influenced by a combination of epidermal growth factor and bromocriptine. Recombinant IL-6 exhibited a significant dose-dependent inhibitory effect on meningioma cell proliferation. The maximum effect was observed at concentrations of 10 to 100 pg/ml, with the decrease in thymidine incorporation ranging from 21% to 35% versus control. Addition of an anti-IL-6 antibody enhanced the growth-stimulating effect of meningioma-derived conditioned medium. The rate of IL-6 secretion tended to show an inverse correlation with meningioma growth rate. The results presented here and the previous results suggest that the regulation of meningioma cell proliferation is defined by a complex network of autocrine stimulation, autocrine inhibition, and influences from multiple exogenous factors.