VAMP4 is required to maintain the ribbon structure of the Golgi apparatus

Abstract

The Golgi apparatus forms a twisted ribbon-like network in the juxtanuclear region of vertebrate cells. Vesicle-associated membrane protein 4 (VAMP4), a v-SNARE protein expressed exclusively in the vertebrate trans-Golgi network (TGN), plays a role in retrograde trafficking from the early endosome to the TGN, although its precise function within the Golgi apparatus remains unclear. To determine whether VAMP4 plays a functional role in maintaining the structure of the Golgi apparatus, we depleted VAMP4 gene expression using RNA interference technology. Depletion of VAMP4 from HeLa cells led to fragmentation of the Golgi ribbon. These fragments were not uniformly distributed throughout the cytoplasm, but remained in the juxtanuclear area. Electron microscopy and immunohistochemistry showed that in the absence of VAMP4, the length of the Golgi stack was shortened, but Golgi stacking was normal. Anterograde trafficking was not impaired in VAMP4-depleted cells, which contained intact microtubule arrays. Depletion of the cognate SNARE partners of VAMP4, syntaxin 6, syntaxin 16, and Vti1a also disrupted the Golgi ribbon structure. Our findings suggested that the maintenance of Golgi ribbon structure requires normal retrograde trafficking from the early endosome to the TGN, which is likely to be mediated by the formation of VAMP4-containing SNARE complexes.

Withdrawal of BDNF from hippocampal cultures leads to changes in genes involved in synaptic function

“…VAMP4 is significant since BDNF is known to regulate presynaptic function through enhanced neurotransmitter release (Lohof et al, 1993;Yano et al, 2006). VAMP4 is also required for maintenance of the ribbon structure of the Golgi apparatus (Shitara et al, 2013). In addition to VAMP4, another gene coding for Golga5-Golgin84; a protein involved in maintaining the Golgi membrane structure was also dramatically reduced by more than 60% after 3 h of BDNF Figure 4 Microarray expression profiles and qPCR validation of select transcripts that were downregulated following BDNF deprivation.…”

Molecular Underpinnings of Synaptic Vesicle Pool Heterogeneity

“…In contrast to syb2 and syb1, which facilitate synchronous evoked release, v‐SNARE VAMP4 facilitates asynchronous evoked release. VAMP4 is better known for its trafficking role in endosomes and the trans‐Golgi network , but it also localizes to synaptic vesicles , although less abundantly than syb2 . Knockdown of VAMP4 in cultured hippocampal neurons reduces the asynchronous phase of inhibitory postsynaptic currents after strong stimulation, and slow calcium chelation inhibits VAMP4‐, but not syb2‐, mediated neurotransmission when these proteins are overexpressed in syb2‐deficient neurons .…”

“…Recently it was discovered that the v‐SNARE vps10p tail interactor 1a (vti1a) participates in spontaneous vesicle recycling. Vti1a localizes mostly to the Golgi apparatus , but at least one splice variant has been identified in synaptic vesicles . Vti1a deficiency does not produce global protein trafficking or developmental deficits , but loss of vti1a in adrenal chromaffin cells reduces the number of dense core vesicles available for hormone secretion .…”

Loss of VAMP5 in mice results in duplication of the ureter and insufficient expansion of the lung

“…VAMP3 plays a role in endocytosis in various types of cells (McMahon et al, 1993), but VAMP3 KO mice develop normally. VAMP4 transcripts were detected in various tissues and it has been shown to regulate trafficking events in the trans-Golgi network and to maintain the ribbon structure of the Golgi apparatus (Advani et al, 1998;Steegmaier et al, 2000;Shitara et al, 2013). VAMP4 KO mice have not been reported.…”