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Chromogranin A, the major lumenal protein in chromaffin granules, controls fusion pore expansion

Upon fusion of the secretory granule with the plasma membrane, small molecules are discharged through the immediately formed narrow fusion pore, but protein discharge awaits pore expansion. Recently, fusion pore expansion was found to be regulated by tissue plasminogen activator (tPA), a protein pre...

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Autores principales: Abbineni, Prabhodh S., Bittner, Mary A., Axelrod, Daniel, Holz, Ronald W.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Rockefeller University Press 2019
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6363410/
https://www.ncbi.nlm.nih.gov/pubmed/30504267
http://dx.doi.org/10.1085/jgp.201812182
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author Abbineni, Prabhodh S.
Bittner, Mary A.
Axelrod, Daniel
Holz, Ronald W.
author_facet Abbineni, Prabhodh S.
Bittner, Mary A.
Axelrod, Daniel
Holz, Ronald W.
author_sort Abbineni, Prabhodh S.
collection PubMed
description Upon fusion of the secretory granule with the plasma membrane, small molecules are discharged through the immediately formed narrow fusion pore, but protein discharge awaits pore expansion. Recently, fusion pore expansion was found to be regulated by tissue plasminogen activator (tPA), a protein present within the lumen of chromaffin granules in a subpopulation of chromaffin cells. Here, we further examined the influence of other lumenal proteins on fusion pore expansion, especially chromogranin A (CgA), the major and ubiquitous lumenal protein in chromaffin granules. Polarized TIRF microscopy demonstrated that the fusion pore curvature of granules containing CgA-EGFP was long lived, with curvature lifetimes comparable to those of tPA-EGFP–containing granules. This was surprising because fusion pore curvature durations of granules containing exogenous neuropeptide Y-EGFP (NPY-EGFP) are significantly shorter (80% lasting <1 s) than those containing CgA-EGFP, despite the anticipated expression of endogenous CgA. However, quantitative immunocytochemistry revealed that transiently expressed lumenal proteins, including NPY-EGFP, caused a down-regulation of endogenously expressed proteins, including CgA. Fusion pore curvature durations in nontransfected cells were significantly longer than those of granules containing overexpressed NPY but shorter than those associated with granules containing overexpressed tPA, CgA, or chromogranin B. Introduction of CgA to NPY-EGFP granules by coexpression converted the fusion pore from being transient to being longer lived, comparable to that found in nontransfected cells. These findings demonstrate that several endogenous chromaffin granule lumenal proteins are regulators of fusion pore expansion and that alteration of chromaffin granule contents affects fusion pore lifetimes. Importantly, the results indicate a new role for CgA. In addition to functioning as a prohormone, CgA plays an important role in controlling fusion pore expansion.
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spelling pubmed-63634102019-08-04 Chromogranin A, the major lumenal protein in chromaffin granules, controls fusion pore expansion Abbineni, Prabhodh S. Bittner, Mary A. Axelrod, Daniel Holz, Ronald W. J Gen Physiol Research Articles Upon fusion of the secretory granule with the plasma membrane, small molecules are discharged through the immediately formed narrow fusion pore, but protein discharge awaits pore expansion. Recently, fusion pore expansion was found to be regulated by tissue plasminogen activator (tPA), a protein present within the lumen of chromaffin granules in a subpopulation of chromaffin cells. Here, we further examined the influence of other lumenal proteins on fusion pore expansion, especially chromogranin A (CgA), the major and ubiquitous lumenal protein in chromaffin granules. Polarized TIRF microscopy demonstrated that the fusion pore curvature of granules containing CgA-EGFP was long lived, with curvature lifetimes comparable to those of tPA-EGFP–containing granules. This was surprising because fusion pore curvature durations of granules containing exogenous neuropeptide Y-EGFP (NPY-EGFP) are significantly shorter (80% lasting <1 s) than those containing CgA-EGFP, despite the anticipated expression of endogenous CgA. However, quantitative immunocytochemistry revealed that transiently expressed lumenal proteins, including NPY-EGFP, caused a down-regulation of endogenously expressed proteins, including CgA. Fusion pore curvature durations in nontransfected cells were significantly longer than those of granules containing overexpressed NPY but shorter than those associated with granules containing overexpressed tPA, CgA, or chromogranin B. Introduction of CgA to NPY-EGFP granules by coexpression converted the fusion pore from being transient to being longer lived, comparable to that found in nontransfected cells. These findings demonstrate that several endogenous chromaffin granule lumenal proteins are regulators of fusion pore expansion and that alteration of chromaffin granule contents affects fusion pore lifetimes. Importantly, the results indicate a new role for CgA. In addition to functioning as a prohormone, CgA plays an important role in controlling fusion pore expansion. Rockefeller University Press 2019-02-04 /pmc/articles/PMC6363410/ /pubmed/30504267 http://dx.doi.org/10.1085/jgp.201812182 Text en © 2019 Abbineni et al. http://www.rupress.org/terms/https://creativecommons.org/licenses/by-nc-sa/4.0/This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms/). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 International license, as described at https://creativecommons.org/licenses/by-nc-sa/4.0/).
spellingShingle Research Articles
Abbineni, Prabhodh S.
Bittner, Mary A.
Axelrod, Daniel
Holz, Ronald W.
Chromogranin A, the major lumenal protein in chromaffin granules, controls fusion pore expansion
title Chromogranin A, the major lumenal protein in chromaffin granules, controls fusion pore expansion
title_full Chromogranin A, the major lumenal protein in chromaffin granules, controls fusion pore expansion
title_fullStr Chromogranin A, the major lumenal protein in chromaffin granules, controls fusion pore expansion
title_full_unstemmed Chromogranin A, the major lumenal protein in chromaffin granules, controls fusion pore expansion
title_short Chromogranin A, the major lumenal protein in chromaffin granules, controls fusion pore expansion
title_sort chromogranin a, the major lumenal protein in chromaffin granules, controls fusion pore expansion
topic Research Articles
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6363410/
https://www.ncbi.nlm.nih.gov/pubmed/30504267
http://dx.doi.org/10.1085/jgp.201812182
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