Biology subjects

Houy, S.

Publications and source records attributed to Houy, S..

4 recordsLinked to original sources

bioRxiv2022

Phorbolester-activated Munc13-1 and ubMunc13-2 exert opposing effects on dense-core vesicle secretion

Munc13 proteins are priming factors for SNARE-dependent exocytosis, which are activated by diacylglycerol (DAG)-binding to their C1-domain. Several Munc13 paralogs exist, but their differential roles are not well understood. We studied the interdependence of phorbolesters (DAG mimics) with Munc13-1 and ubMunc13-2 in mouse adrenal chromaffin cells. Although expression of either Munc13-1 or ubMunc13-2 stimulated secretion, phorbolester was only stimulatory for secretion when ubMunc13-2 expression dominated, but inhibitory when Munc13-1 dominated. Accordingly, phorbolester stimulated secretion in wildtype cells, or cells overexpressing ubMunc13-2, but inhibited secretion in Munc13-2/Unc13b knockout (KO) cells or in cells overexpressing Munc13-1. Phorbolester was more stimulatory in the Munc13-1/Unc13a KO than in WT littermates, showing that endogenous Munc13-1 limits the effects of phorbolester. Imaging showed that ubMunc13-2, but not Munc13-1, traffics to the plasma membrane with a time-course matching Ca2+-dependent secretion, and trafficking is independent of synaptotagmin-7 (syt7). However, in the absence of syt7, phorbolester became inhibitory for both Munc13-1 and ubMunc13-2 driven secretion, indicating that stimulatory phorbolester x Munc13-2 interaction depends obligatorily on functional pairing with syt7. Overall, DAG/phorbolester, ubMunc13-2 and syt7 form a stimulatory triad for dense-core vesicle priming.

neuroscience↗

bioRxiv2021

Dysfunction of exocytosis causes catecholamine hypersecretion in patient with pheochromocytoma

Pheochromocytoma (Pheo) is a neuroendocrine tumor that develops from chromaffin cells of the adrenal medulla, and is responsible of an excess of catecholamines secretion leading to severe clinical symptoms such as hypertension, elevated stroke risk and various cardiovascular complications. Surprisingly, hypersecretory activity of Pheo has never been explored at the cellular and molecular levels from individual tumor cells. In the present study, we have combined catecholamine secretion measurement by carbon fiber amperometry on human tumor cells directly cultured from freshly resected Pheo, with the analysis by mass spectrometry of the exocytotic proteins differentially expressed between the tumor and the matched adjacent non-tumor tissue. Catecholamine secretion recordings from individual Pheo cells obtained from most patients reveal a higher number of exocytic events per cell associated with faster kinetic parameters. Accordingly, we unravel significant tumor-associated modifications in the expression of key proteins involved in different steps of the calcium-regulated exocytic pathway. Altogether, our findings indicate that dysfunction of the calcium-regulated exocytosis at the level of individual Pheo cell is a cause of the tumor-associated hypersecretion of catecholamines.

cancer biology↗

bioRxiv2020

Synaptotagmin-7 places dense-core vesicles at the cell membrane to promote Munc13-2- and Ca2+-dependent priming

The functional consequences of the co-expression of synaptotagmin-1 and synaptotagmin-7 are unclear. We show that when present separately, synaptotagmin-1 and synaptotagmin-7 act as standalone fast and slow Ca2+-sensors for vesicle fusion in mouse chromaffin cells. When present together, synaptotagmin-7 stimulates Ca2+-dependent vesicle priming and inhibits depriming. The priming effect of Synaptotagmin-7 extends to the Readily Releasable Pool, whose fusion is executed by synaptotagmin-1, indicating synergistic action of the two Ca2+-sensors, although they are only partially colocalized. Synaptotagmin-7 promotes ubMunc13-2-dependent priming and the absence of synaptotagmin-7 renders phorbolesters less effective in stimulating priming, although synaptotagmin-7 independent priming is also observed. Morphologically, synaptotagmin-7 places vesicles in close membrane apposition (< 6 nm); in its absence vesicles accumulate out of reach of the fusion complex (20-40 nm). We suggest that a synaptotagmin-7-dependent movement toward the membrane is involved in Munc13-2/phorbolester/Ca2+-dependent priming and sets the stage for fast and slow exocytosis triggering.

neuroscience↗

bioRxiv2019

Endophilin-A controls recruitment, priming and fusion of neurosecretory vesicles

Endophilins-A are conserved endocytic adaptors with membrane curvature-sensing and - inducing properties. We show here that, independently of their role in endocytosis, endophilin-A1 and endophilin-A2 regulate exocytosis of neurosecretory vesicles. The number of neurosecretory vesicles was not altered in chromaffin 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. Endophilins 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 report that endophilins-A, key endocytic proteins linked to neurodegeneration, directly regulate exocytosis by controlling vesicle recruitment, priming and fusion. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=72 SRC="FIGDIR/small/540864v1_ufig1.gif" ALT="Figure 1"> View larger version (16K): org.highwire.dtl.DTLVardef@b5cabeorg.highwire.dtl.DTLVardef@1119afborg.highwire.dtl.DTLVardef@d5da6aorg.highwire.dtl.DTLVardef@1f67e32_HPS_FORMAT_FIGEXP M_FIG C_FIG O_LIRecruitment, priming and fusion of secretory vesicles is controlled by endophilin C_LIO_LILack of endophilins alters the distribution of secretory vesicles near the PM C_LIO_LIEndophilins role in exocytosis is mediated through its SH3-domain C_LIO_LIEndophilin regulates intersectin localization by keeping it away from the PM C_LI

neuroscience↗