Effect of energy deprivation on intracellular transport and secretion of thyroglobulin

Abstract

The effect of energy deprivation on the intracellular transport and secretion of thyroglobulin was studied in open follicles isolated from porcine thyroids. Follicles were pulse-labeled with 3H-leucine or 3H-galactose. Labeled thyroglobulin was secreted into the incubation medium where it was isolated by means of immunoprecipitation. Secretion was followed in chase incubations under various experimental conditions using CCCP (carbonyl-cyanide-mchlorophenylhydrazone) or DNP (dinitrophenol), both uncouplers of oxidative phosphorylation, or CN−, which inhibits respiration. CCCP (1 μM) was shown to inhibit exocytosis by about 80%, DNP (0.1–5 mM) by 45–85%, and CN− (0.5–1.1 mM) by 5–55%. By combining CN− with the ionophore monensin, which blocks transport through the Golgi complex but does not essentially interfere with exocytosis, evidence was obtained that CN− also inhibits transport of thyroglobulin from the Golgi cisternae to the exocytic vesicles by 40%. Electron-miroscopic autoradiography of isolated thyroid lobes from the rat also indicated that transport of 3H-leucine label into the follicle lumen is inhibited in the presence of CCCP or CN−. Intracellular ATP content was found to be about 40% of the control level in follicles incubated with CCCP (1 uM) or CN− (0.9 mM). The results show that the transport of thyroglobulin from the Golgi complex to the exocytic vesicles as well as from the exocytic vesicles into the follicle lumen is dependent upon metabolic energy. The transport blocks are probably associated with inhibited membrane fusions and fissions.