title: The functional role of chromogranins in exocytosis.
abstract: Chromogranins A (CgA) and B (CgB) are the main soluble proteins of large dense-core secretory vesicles (LDCVs). Using CgA- and CgB-knockout (KO) mice, we found that the absence of chromogranins A and B induces significant changes in catecholamine (CA) accumulation and the kinetics of exocytosis. By crossing these two knockout strains, we generated a viable and fertile double CgA/B-KO mouse in which the catecholamine content in chromaffin LDCVs was halved, and the secretory response significantly reduced. Incubating cells with L-DOPA increased the vesicular CA content in wild-type (WT) but not in Cg-KO cells, which was not due to changes in amine transport, or in the synthesis or degradation of cytosolic amines. Electron microscopy revealed the presence of giant secretory vesicles exhibiting significant alterations, with little or no electrodense inner matrix. Proteomic analysis confirmed the absence of CgA and B, and revealed small changes in SgII in the LDCV-enriched fraction, as well as the overexpression of fibrinogen and other proteins. In summary, our findings indicate that the mechanisms responsible for vesicular accumulation of CA are saturated in Cgs-KO cells, in contrast to the ample capacity for further accumulation in WT cells. We conclude that Cgs contribute to a highly efficient system that directly mediates monoamine accumulation and exocytosis in LDCVs.
authors.affiliation: Unidad de Farmacología,, Universidad de La Laguna, 38071 La Laguna, Tenerife, Spain.
authors.forename: Natalia
authors.initials: N
authors.lastname: Domínguez
authors.forename: Judith
authors.initials: J
authors.lastname: Estévez-Herrera
authors.forename: Marta R
authors.initials: MR
authors.lastname: Pardo
authors.forename: Daniel
authors.initials: D
authors.lastname: Pereda
authors.forename: José David
authors.initials: JD
authors.lastname: Machado
authors.forename: Ricardo
authors.initials: R
authors.lastname: Borges
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D019439:Chromaffin Cells / Q000378:metabolism*; D053379:Chromogranin A / Q000235:genetics / Q000502:physiology*; D053378:Chromogranin B / Q000235:genetics / Q000502:physiology*; D005089:Exocytosis / Q000235:genetics / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D022142:Secretory Vesicles / Q000235:genetics / Q000378:metabolism
chemical_list: D053379:Chromogranin A; D053378:Chromogranin B; C506155:chromogranin A, mouse; C506137:chromogranin B, mouse; D002118:Calcium