Mouse VAP33 is associated with the endoplasmic reticulum and microtubules

Abstract

VAMP/synaptobrevin is a synaptic vesicle protein that is essential for neurotransmitter release. Intracellular injection of antisera against the Aplysia californica VAMP/synaptobrevin-binding protein ApVAP33 inhibited evoked excitatory postsynaptic potentials (EPSPs) in cultured cells, suggesting that this association may regulate the function of VAMP/synaptobrevin. We have identified and characterized a mouse homologue of ApVAP33, mVAP33. The overall domain structure of the proteins is conserved, and they have similar biochemical properties. mVAP33 mRNA is detectable in all mouse tissues examined, in contrast to the more restricted expression seen in A. californica. We analyzed the cellular distribution of mVAP33 protein in brain slices and cultured cortical cells by light and electron microscopy. Although present at higher levels in neurons, immunoreactivity was detected throughout both neurons and glia in a reticular pattern similar to that of endoplasmic reticulum-resident proteins. mVAP33 does not colocalize with VAMP/synaptobrevin at synaptic structures, but expression overlaps with lower levels of VAMP/synaptobrevin in the soma. Ultrastructural analysis revealed mVAP33 associated with microtubules and intracellular vesicles of heterogeneous size. In primary neuronal cultures, large aggregates of mVAP33 are also detected in short filamentous structures, which are occasionally associated with intracellular membranes. There is no evidence for accumulation of mVAP33 on synaptic vesicles or at the plasma membrane. These data suggest that mVAP33 is an endoplasmic-reticulum-resident protein that associates with components of the cytoskeleton. Any functional interaction between mVAP33 and VAMP/synaptobrevin, therefore, most likely involves the delivery of components to synaptic terminals rather than a direct participation in synaptic vesicle exocytosis.

Differential Regulation of Endoplasmic Reticulum Structure through VAP-Nir Protein Interaction

“…These diverse functions have been demonstrated in different species and cell types, and are mediated by different members of this family. Nevertheless, the overall structures of VAP proteins are similar and consist of a large N-terminal region facing the cytoplasm and a hydrophobic C terminus that functions as a transmembrane domain (TMD) (20). The cytoplasmic region contains a conserved N-terminal domain of 100 amino acids, which shares high sequence similarity with the nematode major sperm protein (MSP).…”

“…Subsequent studies demonstrated the interaction of the mammalian VAP-A with additional SNAREs, including syntaxin 1A, rbet1, rsec22, ␣SNAP, and NSF (29). VAP-A also interacts with the tight junction protein occludin (22), with microtubules (20,24), and with OSBP (oxysterol-binding protein) (28). In this study, we isolated VAP-B as an interacting protein with Nir2, using a pull-down experiment and mass spectrometry analysis.…”

“…VAP-B is also a type II integral membrane protein of ϳ31 kDa that has been previously localized to the ER and the pre-Golgi intermediates (19,20). It belongs to a highly conserved family of proteins, which are implicated in the regulation of neurotransmitter release, ER-Golgi and intra-Golgi transport, Glu4 (glucose transporter 4) trafficking, stabilization of presynaptic microtubules, and the expression of phospholipid biosynthetic genes (19,(21)(22)(23)(24)(25).…”

Protein Phosphatase 2Cϵ Is an Endoplasmic Reticulum Integral Membrane Protein That Dephosphorylates the Ceramide Transport Protein CERT to Enhance Its Association with Organelle Membranes

“…Vesicle-associated membrane protein-associated protein A (VAPA) 3 is an endoplasmic reticulum (ER)-resident type II transmembrane protein with homologs widely distributed from yeast to human (1)(2)(3). Recently, evidence has accumulated that in mammalian cells VAPA participates in the regulation of inter-organelle transport of membrane lipids by recruiting lipid transfer proteins to the ER membrane.…”

Vesicle‐associated protein‐A is differentially expressed during intestinal smooth muscle cell differentiation

“…First, VAP-A is known to play an important role in mediating cellular exocytosis in numerous cell types, including SMCs (Sollner et al, 1993;Skehel et al, 1995Skehel et al, , 2000Sudhof, 1995;Rothman and Sollner, 1997;Weber et al, 1998;Weir et al, 2001). A variety of studies indicate that SMCs are capable of responding to and modifying their microenvironment by the secretion of cytokines, growth factors, and extracellular matrix (Simon-Assman et al, 1990Burgess and Sizeland, 1990;Simo et al, 1991;Perr et al, 1992; One such transcript, identified as T2 (arrowhead), was differentially expressed in immature smooth muscle myocytes in three separate reactions composed of multiple concentrations of distinct tcRNA preparations both in the presence and absence of DNAse 1.…”