Insulin binds to specific receptors and stimulates macromolecular synthesis in C 6 glioma cells

Summary

The existence of insulin receptors and biological responces to insulin on macromolecular synthesis have been studied in C6 glioma cells. Binding of¹²⁵I-insulin to C6 glioma cells was specific, time-and PH-dependent. Porcine insulin competed for¹¹²⁵I-insulin binding in a dose-dependent manner. Unlabeled polypeptides, including glucagon, bovine growth hormone, bovine prolactin did not compete for¹²⁵I-insulin binding. Scatchard analysis of the binding data gave a curvilinear plot which may indicate negative co-operativity or the existence of both high and low affinity (Ka=7.55 × 10¹⁰ −4.25 × 10⁹) sites.

Incubation of cultures with insulin caused a time and dose-dependent stimulation of DNA, RNA and protein synthesis in C 6 glioma cells (measured by³H-thymidine,³H-uridine or³H-leucine incorporation into DNA, RNA, or protein respectively). The increase of macromolecular synthesis was admitted at more than 2 nM concentration of insulin. Maximal stimulation of DNA synthesis (142% of control) occurred 6 hours after incubation with 167 nM insulin. The same concentration of insulin caused a 45% increase in 1 hour on RNA synthesis, a 37% increase in 2 hour on protein synthesis.

These results indicate that C 6 glioma cells have specific insulin receptors capable of mediating effects of insulin on macromolecular synthesis. Insulin in the brain and even blood may be an important growth factor in the glioma cells of the patients with disrupted bloodbrain-barrier.