Glycoprotein III (Clusterin, Sulfated Glycoprotein 2) in Endocrine, Nervous, and Other Tissues: Immunochemical Characterization, Subcellular Localization, and Regulation of Biosynthesis

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Abstract
Specific antisera were raised against the A and B chains of glycoprotein III. lmmunoblotting revealed that in adrenal medulla both chains migrate very closely together in two‐dimensional electrophoresis. Both chains with slightly differing molecular sizes are found in several endocrine tissues and in brain, kidney, liver, and serum. The mRNA has an analogous widespread distribution. In primary cultures of chromaffin cells the level of message becomes significantly increased by treatment with hista‐mine or 12‐O‐tetradecanoylphorbol 13‐acetate/forskoIin. However, the increase is small when compared with that of secretogranin II. The subcellular localization of glycoprotein III in endocrine organs and in the posterior pituitary was investigated by subcellular fractionation and immuno‐electron microscopy. Glycoprotein III was found to be confined to the large densecore vesicles of these organs. For a discussion of the function of glycoprotein III, its localization in these organelles has to be taken into account.