Interaction between secretogranin III and carboxypeptidase E facilitates prohormone sorting within secretory granules

Abstract

Secretogranin III (SgIII) and carboxypeptidase E (CPE) bind specifically to cholesterol-rich secretory granule (SG) membranes. We previously showed that SgIII binds chromogranin A (CgA) and targets CgA to the SGs in endocrine cells. We investigated the binding of SgIII and CPE because they frequently localize close to the periphery of SGs, and they bind each other in mouse corticotrope-derived AtT-20 cells. In Cpefat mouse corticotropes, which have defective CPE, proopiomelanocortin (POMC)-derived adrenocorticotrophin hormone (ACTH)-containing peptides were distributed over the entire surface of the SGs, and displayed a regulated secretion by secretagogues. The Cpefat pituitary exhibited elevated levels of SgIII and CgA, which suggests that they compensate for a sorting function of CPE for POMC and its intermediates to ACTH. Indeed, both SgIII and CgA were able to bind POMC-derived intermediates. In a competitive pull-down assay, excessive SgIII led to a decrease in CPE-bound POMC-derived intermediate molecules, and SgIII pulled-down by anti-ACTH antibody increased proportionately. We suggest that SgIII and CPE form the separate functional sorting complex by anchoring to cholesterol-rich SG membranes, and POMC-derived peptides are transferred from CPE to SgIII, and subsequently to CgA.

Beta cell chromogranin B is partially segregated in distinct granules and can be released separately from insulin in response to stimulation

“…Pancreatic beta cells and beta cell lines are also known to synthesise, in addition to insulin, a number of other secretory proteins, including members of the granin family, chromogranin A and chromogranin B (CgB) [7][8][9][10]. Based on intracellular distribution studies [7,8] and on data obtained in other cell lines (AtT20 and PC12), these granins are believed to play important roles both in the sorting, packaging and processing of secretion products [11][12][13][14], and in the storage of Ca 2+ within SG lumina [15]. Moreover chromogranin A and/or peptides derived from its processing have been reported to play autocrine, paracrine and endocrine functions upon discharge [16][17][18][19], while CgB has been shown to induce an autocrine inhibition of insulin release from beta cells [20].…”

Secretogranin III Directs Secretory Vesicle Biogenesis in Mast Cells in a Manner Dependent upon Interaction with Chromogranin A

“…It is clear that CgA and CgB act as cargo precursors that are proteolytically cleaved to form bioactive peptides. In addition to being sources of granule content in the form of proteolytically derived peptides, Chromogranins have also been described to chaperone secretory granule components (1,3,9,33,34). Chromogranins have also been described as cholesterol binding proteins, and a model for their role in the cholesterol sequestration events that participate in granulogenesis has been derived from several studies (35).…”

“…Thus, in mast cells, as in sympathoadrenal AtT-20 cells (16,35), a functional interaction between SgIII and CgA seems to be required for their granulogenic capacity. Hosaka and coauthors (34,35) have suggested that SgIII binds to the amino terminus of CgA thereby initiating the secretory granule biogenesis in the AtT-20 cells. This SgIIICgA complex binds to the cholesterol moieties within the secretory granule membrane, but the exact mechanism by which this binding promotes granulogenesis is not yet fully understood.…”

A nanotechnological, molecular-modeling, and immunological approach to study the interaction of the anti-tumorigenic peptide p28 with the p53 family of proteins

“…42 GST fused to the p63 DBD was immobilized on beads, followed by incubation in the presence or absence of p28 (10-100 mole excess). Whole-cell lysates containing Cop1 and Pirh2 were prepared from MCF-7 cells in PBS containing 0.1% Triton X-100, 10% glycerol, and a protease inhibitor cocktail (Sigma-Aldrich).…”