Biophysical Society Thematic Meeting| Padova 2019

Quantitative Aspects of Membrane Fusion and Fission

Thursday Speaker Abstracts

NOVEL FUNCTIONS OF ENDOPHILINS-A IN EXOCYTOSIS AND MEMBRANE TRAFFICKING Sindhuja Gowrisankaran 1 ; Vicky Steubler 1 ; Sébastien Houy 3 ; Johanna Peña del Castillo 1 ; Monika Gelker 1 ; Jana Kroll 1 ; Nuno Raimundo 4 ; Jakob B. Sørensen 3 ; Ira Milosevic 1,2 ; 1 European Neuroscience Institute (ENI), Synaptic Vesicle Dynamics, Göttingen, Niedersachsen, Germany 2 University Medical Center Göttingen (UMG), Göttingen, Niedersachsen, Germany 3 University of Copenhagen, Department for Neuroscience, Copenhagen, Hovedstaden, Denmark 4 University Medical Center Göttingen (UMG), Institute for Cellular Biochemistry, Göttingen, Niedersachsen, Germany Release of vesicular content by exocytosis governs numerous biological events, including neurotransmission and neuromodulation. Following exocytosis, endocytosis retrieves the exocytosed vesicle membrane and proteins. Two processes are tightly coordinated, but molecular mechanisms underlying such coupling are not well understood. Endophilins-A are conserved endocytic adaptors with membrane curvature-sensing and -inducing properties, known to orchestrate various steps in clathrin-dependent and clathrin-independent endocytosis. We have found that, independently of their key roles in endocytosis, endophilin-A1 and endophilin-A2 regulate exocytosis of neurosecretory vesicles. The number of neurosecretory vesicles was not altered in cells without endophilin, yet fast capacitance and amperometry measurements revealed reduced exocytosis, smaller vesicle pools and changed fusion kinetics. Both endophilin-A1 (brain-enriched) and A2 (ubiquitous) rescued exocytic defects, but endophilin-A2 was more efficient. Distribution of neurosecretory vesicles was altered in the plasma membrane proximity, but levels and distributions of main exocytic and endocytic factors were unchanged, and slow compensatory endocytosis was not robustly affected. Endophilin’s role in exocytosis is mediated through its SH3-domain and, at least in part, interaction with intersectin, a coordinator of exocytic and endocytic traffic. Altogether, we discovered that endophilins-A, key endocytic proteins linked to neurodegeneration, also regulate exocytosis by controlling vesicle recruitment, priming and fusion.

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