Texas-Red-asialoorosomucoid (ASOR) fluorescence-sorted early and late endocytic vesicles from rat liver were subjected to proteomic analysis with the aim of identifying functionally important proteins. Several Rab GTPases, including Rab1a, were found. The present study immunolocalized Rab1a to early and late endocytic vesicles and examined its potential role in endocytosis. Huh7 cells with stable knockdown of Rab1a exhibited reduced endocytic processing of ASOR. This correlated with the finding that Rab1a antibody reduced microtubule-based motility of rat-liver-derived early but not late endocytic vesicles in vitro. The inhibitory effect of Rab1a antibody was observed to be specifically towards minus-end-directed motility. Total and minus-end-directed motility was also reduced in early endocytic vesicles prepared from Rab1a-knockdown cells. These results corresponded with virtual absence of the minus-end-directed kinesin Kifc1 from early endocytic vesicles in Rab1a knockdown cells and imply that Rab1a regulates minus-end-directed motility largely by recruiting Kifc1 to early endocytic vesicles.
"RAB1A localises predominantly to the ERGIC membrane and recruits the tethering factor p115 to the COPII coated vesicles, facilitating the formation of a fusion complex and thus directing COPII vesicles to the Golgi for delivery of their cargo (Allan et al., 2000). However, in addition to its function in ER to Golgi transport, RAB1A is also involved in early Golgi trafficking (Yamasaki et al., 2009), the motility of early endocytotic vesicles, early endosome to Golgi trafficking (Mukhopadhyay et al., 2011), regulation of the actin cytoskeleton (Kicka et al., 2011), recycling of the integrin protein ITGB1 to the cell surface (Wang et al., 2010) and autophagy (Winslow et al., 2010). RAB1A is therefore a multifunctional protein with roles in varied cellular processes. "
"Rab1 exists as two isoforms (Rab1a and Rab1b) that are thought to be largely functionally redundant in the early secretory pathway (Tisdale et al., 1992), while Rab1a is also reported to play a role in early-endosome-to-Golgi trafficking (Mukhopadhyay et al., 2011; Sclafani et al., 2010) and autophagy (Winslow et al., 2010). In the early secretory pathway, Rab1 is required for membrane recruitment of GBF1 (Dumaresq-Doiron et al., 2010; Monetta et al., 2007; Nuoffer et al., 1994; Schwartz et al., 2007) and vesicular transport between the ER and Golgi compartments (Allan et al., 2000; Bannykh et al., 2005; Monetta et al., 2007; Pind et al., 1994; Plutner et al., 1990). "
[Show abstract][Hide abstract] ABSTRACT: Picornaviruses replicate their genomes in association with cellular membranes. While enteroviruses are believed to utilise membranes of the early secretory pathway the origin of the membranes used by FMDV for replication are unknown. Secretory vesicle traffic through the early secretory pathway is mediated by the sequential acquisition of two distinct membrane coat-complexes, COPII and COPI and requires the coordinated actions of Sar1, Arf1 and Rab proteins. Sar1 is essential for generating COPII vesicles at ER exit sites while Arf1 and Rab1 are required for subsequent vesicle transport by COPI vesicles. In this present study, we provided evidence that FMDV requires pre-Golgi membranes of the early secretory pathway for infection. siRNA depletion of Sar1 or expression of a dominant-negative (DN) mutant of Sar1a inhibited FMDV infection. In contrast, a dominant-active mutant of Sar1a, which allows COPII vesicle formation but inhibits the secretory pathway by stabilizing COPII coats, caused major disruption to the ERGIC but did not inhibit infection. Treatment of cells with brefeldin-A, or expression of DN mutants of Arf1 and Rab1a disrupted the Golgi and enhanced FMDV infection. These results show that reagents that block the early secretory pathway at ER exit sites have an inhibitory effect on FMDV infection while reagents that block the early secretory pathway immediately after ER exit but before the ERGIC and Golgi make infection more favourable. Together these observations argue for a role for Sar1 in FMDV infection and that initial virus replication takes place on membranes that are formed at ER exit sites.
Journal of General Virology 08/2013; 94(Pt 12). DOI:10.1099/vir.0.055442-0 · 3.18 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The acrosome is a unique membranous organelle located over the anterior part of the sperm nucleus that is highly conserved throughout evolution. This acidic vacuole contains a number of hydrolytic enzymes that, when secreted, help the sperm penetrate the egg's coats. Although acrosome biogenesis is an important aspect of spermiogenesis, the molecular mechanism(s) that regulates this event remains unknown. Active trafficking from the Golgi apparatus is involved in acrosome formation, but experimental evidence indicates that trafficking of vesicles out of the Golgi also occurs during acrosomogenesis. Unfortunately, this second aspect of acrosome biogenesis remains poorly studied. In this article, we briefly discuss how the biosynthetic and endocytic pathways, assisted by a network of microtubules, tethering factors, motor proteins and small GTPases, relate and connect to give rise to the sperm-specific vacuole, with a particular emphasis placed on the endosomal compartment. It is hoped that this information will be useful to engage more studies on acrosome biogenesis by focusing attention towards suggested directions.
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