Regulation of tubulin synthesis in islets of Langerhans.

Abstract

Tubulin represents a major protein in rat pancreatic islets, which averages 0.5% of the total protein content and 6% of the noninsulin protein synthesized under basal metabolic conditions. Glucose increases the synthesis of tubulin 2- to 3-fold. Tubulin synthesis is also stimulated by cyclic[c]AMP in both the absence and presence of glucose; this effect of cAMP occurs preferential to noninsulin protein synthesis at physiological glucose concentrations. Tubulin synthesis was decreased more than 75% by fasting, an effect prevented by maintaining animals on glucose exclusively. The fasting-induced reduction in tubulin synthesis is corrected in vitro by increasing cAMP levels. These findings parallel changes previously reported in insulin release and suggest that physiological agents can exert their insulin secretory action through an effect upon the rate of tubulin synthesis.