VAMP2 is implicated in the secretion of antibodies by human plasma cells and can be replaced by other synaptobrevins

Abstract

The production and secretion of antibodies by human plasma cells (PCs) are two essential processes of humoral immunity. The secretion process relies on a group of proteins known as soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs), which are located in the plasma membrane (t-SNAREs) and in the antibody-carrying vesicle membrane (v-SNARE), and mediate the fusion of both membranes. We have previously shown that SNAP23 and STX4 are the t-SNAREs responsible for antibody secretion. Here, using human PCs and antibody-secreting cell lines, we studied and characterized the expression and subcellular distribution of vesicle associated membrane protein (VAMP) isoforms, demonstrating that all isoforms (with the exception of VAMP1) are expressed by the referenced cells. Furthermore, the functional role in antibody secretion of each expressed VAMP isoform was tested using siRNA. Our results show that VAMP2 may be the v-SNARE involved in vesicular antibody release. To further support this conclusion, we used tetanus toxin light chain to cleave VAMP2, conducted experiments to verify co-localization of VAMP2 in antibody-carrying vesicles, and demonstrated the coimmunoprecipitation of VAMP2 with STX4 and SNAP23 and the in situ interaction of VAMP2 with STX4. Taken together, these findings implicate VAMP2 as the main VAMP isoform functionally involved in antibody secretion.

Differential epigenetic regulation between the alternative promoters, PRDM1α and PRDM1β, of the tumour suppressor gene PRDM1 in human multiple myeloma cells

“…Western blotting was performed previously described 61 . Fifty micrograms of total protein lysates were added to each well.…”

Endosomal and Phagosomal SNAREs

“…The essential (161) Qbc-SNARE SNAP23 is best known for its role in plasma membrane trafficking. SNAP23 mediates exocytosis in many cell types (109,110,174,178,219,234,256,312,346), for instance in neurons where it mediates the post-synaptic surface delivery of the glutamate receptor at dendritic spines (296). The Qb-and Qc-SNARE-motifs of SNAP23 are connected by a linker region containing five palmitoylated cysteines (272) that anchor it at the plasma membrane, recycling and late endosomes, and the trans-Golgi network (88,94,104,109,166,223,275,309,312,346).…”

“…VAMP2 knockout mice die immediately after birth, because of the absence of neurotransmitter release from neurons (which do not contain compensatory VAMP3) (36). Although VAMP2 is predominantly expressed in neurons and neuroendocrine cells, it also mediates exocytosis in nonneuronal cell types (110,162,174,202), mainly by complexing with Stx4 (Qa) and SNAP23 (Qbc) (110,162,174,202,205,211,308). In addition, VAMP2 facilitates the membrane growth for phagocytosis by mediating local fusion of endosomes with the plasma membrane at the site of uptake (123).…”

Alpha synuclein in hematopoiesis and immunity

“…All isoforms of VAMP family, except for VAMP1, have been identified in human plasma cells at different levels of expression. For example, VAMP2 is responsible for secretion of antibodies from plasma cells [133]. Likewise, SNAP-23 [134] and syntaxin-4 [135] have been identified as the corresponding t-SNARE proteins mediating antibody secretion.…”