Delivery and final fusion of the secretory vesicles with the relevant
April 18, 2017
Delivery and final fusion of the secretory vesicles with the relevant target membrane are hierarchically organized and reciprocally interconnected multi-step processes involving not only specific protein-protein relationships but also specific protein-phospholipid interactions. directly affects cortical cytoskeleton and PM dynamics. Here we summarize the current knowledge on exocyst-cytoskeleton-PM relationships in order to open a perspective for future research in this area in flower cells. and exocyst parts and and GTPases regulating the exocyst polar focusing on (Wu et al. 2008 An interesting reciprocal relationship was observed during cell wounding response where Sec3p and the Bni1p formin are degraded in order to get rid of competition for secretory vesicles required to restoration the damaged membrane and cell wall which are arriving along the pre-polarized cytoskeleton directing current polarized growth. The Bnr1p formin and the Exo70p exocyst subunit relocalize to the damage site followed by redistribution of the Myo2p myosin and delivery of fresh material (Kono et al. 2012 In budding candida cell polarity and polarized exocytosis is definitely coordinated also from the Rho3p GTPase (Adamo et al. 1999 which can regulate both actin polarity and transport WAY-362450 of exocytic vesicles from mother cell to the bud as well as vesicle docking to the PM. While the Rho3p vesicle delivery function is definitely mediated by Myo2p the docking requires Exo70p (Adamo et al. 1999 In the fission candida and double mutants are still capable of polarized growth (Bendezú and Martin 2011 Although all fission candida exocyst subunits can localize to cell poles mainly independently of the actin cytoskeleton at least Sec3 Sec5 and Exo70 (most probably as a part of the complete exocyst complex) are more efficiently transported to the cell apex from the Myo52 myosin V along microfilaments (Snaith et al. 2011 Bendezú et al. 2012 Either practical Sec3 or Exo70 is essential for viability and appropriate localization of additional exocyst subunits suggesting that as with budding candida these two parts act as exocyst tethers in the PM (Bendezú et al. 2012 A polarization pathway involving the exocyst relocalization and actin repolarization downstream of Cdc42 also participates in fission candida mating (Bendezú and Martin 2013 Unexpectedly the fission candida Sec3 not only functions in exocytosis but also marks sites for actin recruitment and settings overall actin business via direct binding of For3 (Jourdain et al. 2012 Mutants WAY-362450 in Sec3 show lack of microfilaments depolarized actin patches and disassembly of the cytokinetic actomyosin ring probably due to a failure in polarization of the For3 formin. The Exo70 exocyst subunit also interacts both and with the yeast and rat Arpc1/Arc40 subunit of the Arp2/3 complex a key regulator of actin polymerization. Inhibition of the Exo70 function in rat kidney cells blocks formation of actin-based membrane protrusions and affects cell migration (Zuo et al. 2006 pointing to yet unknown capacity of Exo70 to regulate the actin business and coordinating thus actin cytoskeleton with membrane trafficking during WAY-362450 cell migration. Exo70 was recently shown to promote Arp2/3-driven microfilament nucleation and WAY-362450 branching (Liu et al. 2012 Because both the exocyst and Arp2/3 complexes are well conserved across eukaryotes including plants their interaction is likely to be conserved as well. In mammalian cells actin business as well as membrane trafficking cell growth and differentiation is usually regulated by RalA and RalB ubiquitous small GTPases from the Ras superfamily (Feig et al. 1996 Activated (GTP-bound) RalA forms a stable complex with the exocyst via binding to Sec5 (Brymora et al. 2001 Sugihara et al. 2002 Fukai et al. 2003 and Exo84 (Moskalenko et al. 2003 Jin et al. 2005 exocyst STAT91 subunits in human and rat cells. Specific inhibition of the Sec5 activity blocks filopodia formation in 3T3 cells WAY-362450 a dynamic process that is highly dependent on actin reorganization and that can be normally induced by RalA or cytokines via Cdc42 (Sugihara et al. 2002 This inhibitory effect could not be attributed to disrupted secretion since inhibition of secretion by brefeldin A did not affect filopodia formation (Sugihara et al. 2002 indicating that the exocyst-RalA complex may regulate actin.