Biophysical Society Conference | Estes Park 2023

Membrane Budding and Fusion

Monday Speaker Abstracts

MEMBRANE FUSION AND FISSION: LESSONS FROM UNEXPECTED PLACES

Erdem Karatekin ; 1 Yale University, Cellular and Molecular Physiology, New Haven, CT, USA

In mammalian cells specialized for secretion, why do some secretory vesicles collapse rapidly into the plasma membrane after fusing with it, while some others undergo reuptake nearly intact? In bacteria, how does membrane fission occur during endospore formation? I will show evidence that in both cases cell membrane flows, driven by membrane tension gradients, seems to be critical.

MOLECULAR REGULATION OF ATRIAL NATRIURETIC PEPTIDE SECRETION IN CARDIOMYOCYTES BY THE RAB3GAP1 AND THE RAB3A GTPASE CYCLE

Kobina Essandoh 1 ; Arasakumar Subramani 1 ; James P Teuber 1 ; Matthew J Brody 1,2 ; 1 University Of Michigan, Pharmacology, Ann Arbor, MI, USA 2 University of Michigan, Internal Medicine, Division of Cardiovascular Medicine, Ann Arbor, MI, USA

Despite the clinical relevance to cardiovascular disease, molecular regulation of atrial natriuretic peptide (ANP) release by cardiomyocytes remains ill-defined. We uncovered novel functions for Rab3gap1 and modulation of Rab3a nucleotide cycling in membrane fusion and atrial natriuretic peptide (ANP) release. We previously generated transgenic mice overexpressing the Golgi localized S-acyltransferase, zDHHC9, and identified Rab3gap1 as a novel cardiac substrate of zDHHC9. Rab3gap1 palmitoylation and retention at the cardiomyocyte Golgi, Rab3a-GTP levels, and formation of Rab3a-positive post-Golgi vesicles were all enhanced in zDHHC9 overexpressing hearts as were Rab3gap1, Rab3a, and ANP atrial protein levels but circulating ANP levels were reduced, suggesting a defect in ANP secretion. Notably, treatment of cardiomyocytes with the secretagogue phenylephrine (PE) promoted substantial ANP release as expected, but also enhanced Rab3gap1 palmitoylation and Rab3a GTP-loading and peripheral vesicle formation, whereas knockdown of zDHHC9 repressed these PE-induced effects on Rab3gap1 and Rab3a but further enhanced PE-stimulated ANP secretion, suggesting zDHHC9 mediated palmitoylation of Rab3gap1 serves as an intrinsic mechanism to limit ANP release. Consistent with a role for Rab3a nucleotide exchange in modulation of ANP release, overexpression of Rab3gap1 in cardiomyocytes promoted a profound increase in ANP release whereas a GAP-deficient mutant of Rab3gap1 (Rab3gap1 R728A ) was resistant to this effect. Collectively, these data suggest disruption of Rab3a nucleotide cycling perturbs secretory vesicle membrane fusion and ANP release in cardiac myocytes and establish critical roles for Rab3a activity and its modulation by zDHHC9-mediated palmitoylation of Rab3gap1 in governing cardiac homeostasis and endocrine signaling. Future studies in mice with cardiomyocyte-specific deletion of Rab3gap1 and zDHHC9 will further examine the necessity of Rab3a GTP:GDP exchange on ANP secretion and blood pressure homeostasis in vivo.

12