Cheng-Chun Wang, Chee Peng Ng, Hong Shi, Hwee Chien Liew, Ke Guo, Qi Zeng, and Wanjin Hong
Vesicle-associated membrane proteins (VAMPs) belong to the soluble
N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) family of proteins which are essential for driving membrane fusion in intracellular vesicle trafficking. Among the seven mammalian VAMPs, VAMP1 and VAMP2 are known to function in mediating release of neurotransmitters while the ubiquitously expressed VAMP3 appears to be non-essential in vivo. The physiological roles of VAMP4, 5 and 7 remain elusive. VAMP8 was initially identified as an endosomal SNARE protein in cultured cells. However, our recent studies in knockout mice have revealed that it is located on secretory granules and plays a critical role in the regulated exocytic pathway in non-neuronal tissues such as the exocrine system. In the current study, we focus on the renal phenotype of the VAMP8 knockout mice. Our results demonstrate that VAMP8 is involved in surface deployment of AQP2 in response to vasopressin. Although previous in vitro studies have implicated VAMP2 and VAMP3 in AQP2 trafficking, our investigation represents the first physiologically-relevant study showing a major role of VAMP8 in AQP2 exocytosis.
Figure Legend: Immunoelectron microscopy study of AQP2 trafficking in vivo. Wild-type (+/+) and VAMP8-null (-/-) mice were left untreated or were injected with DDAVP at 1 ng/kg. Mice were sacrificed at 30 min after DDAVP stimulation, and kidneys were perfusion-fixed with 2% PLP for 30 min before being subjected to immunogold labeling for the detection of AQP2. Scale bar, 200 nm. PM, plasma membrane.
published in Molecular and Cellular Biology, 2009 Oct 19. [Epub ahead of print]
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