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Inhibition of glia maturation factor-induced mitogenesis in glioblasts by calmodulin antagonists
Abstract:
The growth inhibitory activity of calmodulin antagonist, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) and trifluoperazine (TFP), was analyzed by the use of rat fetal glioblasts stimulated by glia maturation factor (GMF) or rat astrocytoma cells (C6). The inhibitory effect of W-7 on GMF-induced DNA synthesis of glioblasts was apparent when the drug was added within 10 h after the stimulation by GMF (late G1 phase), but was not shown when W-7 was added at 12 h or later (S phase). The intracellular calmodulin content was built up concurrently with the increase in the DNA synthesis in S phase. The half-maximal inhibition (ID50) of GMF-induced DNA synthesis in glioblasts was observed at 16.5 microM of W-7 or 9.0 microM of TFP. ID50 of DNA synthesis in exponentially growing C6 cells was approximately 3 times higher than that in glioblasts: 24 microM of TFP and as high as 40 microM of W-7. ID50 of growth rate of C6 cells was 15 microM of TFP which was comparable to the ID50 dose for the inhibition of DNA synthesis. Both calmodulin antagonists and W-5, a dechlorinated analog of W-7, however, elicited a curious activation of DNA synthesis of glioblasts at low concentrations (lower than 10 microM of W-7 and W-5, or lower than 5 microM of TFP), indicating non-specific effects of calmodulin antagonists on DNA synthesis. These results suggest that calmodulin antagonists have two conflicting effects on DNA synthesis: the stimulation of DNA synthesis at lower concentrations, and inhibition at higher concentrations.
Insights
Calmodulin antagonists like W-7 and TFP inhibit glioblast DNA synthesis when applied early, but not later. These compounds show dual effects, stimulating DNA synthesis at low concentrations and inhibiting it at higher concentrations.
Area of Science:
- Neuroscience
- Cell Biology
- Pharmacology
Background:
- Calmodulin plays a crucial role in cellular processes, including cell growth and proliferation.
- Calmodulin antagonists are drugs that inhibit the function of calmodulin.
- Understanding the effects of calmodulin antagonists on cell proliferation is important for potential therapeutic applications.
Purpose of the Study:
- To investigate the growth inhibitory activity of calmodulin antagonists N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) and trifluoperazine (TFP).
- To determine the effects of these antagonists on DNA synthesis and cell growth in rat fetal glioblasts and rat astrocytoma cells (C6).
- To elucidate the concentration-dependent effects and potential non-specific actions of calmodulin antagonists on DNA synthesis.
Main Methods:
- Treatment of rat fetal glioblasts with glia maturation factor (GMF) followed by administration of W-7 or TFP at different time points.
- Treatment of rat astrocytoma cells (C6) with W-7 or TFP.
- Measurement of DNA synthesis and cell growth rates.
- Analysis of intracellular calmodulin content.
Main Results:
- W-7 inhibited GMF-induced DNA synthesis in glioblasts when added within 10 hours (late G1 phase) but not later (S phase).
- The half-maximal inhibitory concentration (ID50) for GMF-induced DNA synthesis in glioblasts was 16.5 microM for W-7 and 9.0 microM for TFP.
- ID50 values for C6 cells were higher (40 microM for W-7, 24 microM for TFP for DNA synthesis; 15 microM for TFP for growth rate).
- Low concentrations of W-7, W-5, and TFP paradoxically activated glioblast DNA synthesis, suggesting non-specific effects.
Conclusions:
- Calmodulin antagonists exhibit dual effects on DNA synthesis: stimulation at low concentrations and inhibition at high concentrations.
- The timing of antagonist application is critical for observing inhibitory effects on GMF-induced glioblast DNA synthesis.
- Calmodulin antagonists demonstrate differential sensitivity between normal glioblasts and C6 astrocytoma cells, with implications for understanding cell proliferation regulation.