RalA-exocyst-dependent Recycling Endosome Trafficking Is Required for the Completion of Cytokinesis

Abstract

In eukaryotic cells, recycling endosome-mediated trafficking contributes to the completion of cytokinesis, in a manner under the control of the centrosome. We report that the exocyst complex and its interacting GTPase RalA play a critical role in this polarized trafficking process. RalA resides in the recycling endosome and relocates from the pericentrosomal region to key cytokinetic structures including the cleavage furrow, and later, the abscission site. This event is coupled to the dynamic redistribution of the exocyst proteins. These associate with the centrosome in interphase and concentrate on the central spindle/ midbody during cytokinesis. Disruption of RalA-exocyst function leads to cytokinesis failure in late stages, particularly abscission, resembling the cytokinesis defects induced by loss of centrosome function. These data suggest that RalA and the exocyst may regulate vesicle delivery to the centrosome-related abscission site during the terminal stage of cytokinesis, implicating RalA as a critical regulator of cell cycle progression.

The Exocyst at a Glance

“…In metazoans, Ral GTPases (RalA and RalB) interact with both Sec5 and Exo84, and these interactions have been implicated in many processes, including cell migration, autophagy, neurogenesis and cancer (Brymora et al, 2001;Sugihara et al, 2002;Moskalenko et al, 2002Moskalenko et al, , 2003Polzin et al, 2002;Balakireva et al, 2006;Bodemann et al, 2011;Chen et al, 2006Chen et al, , 2007Chien et al, 2006;Hazelett et al, 2011;Lalli, 2009;Rosse et al, 2006). Cell fractionation studies have shown that Sec5 and Exo84 are in separate sub-complexes (Moskalenko et al, 2003), and structure analysis has demonstrated that Sec5 and Exo84 competitively bind to GTP-Ral (Jin et al, 2005).…”

“…In Arabidopsis, the exocyst subunits are localized to the separation sites during initiation of the cell plate and maturation, when vesicle fusion is in high demand (Fendrych et al, 2010). In mammalian cells, the exocyst is involved in the trafficking of secretory vesicles to the cleavage furrow and midbody under the control of Rab11 and RalA (Chen et al, 2006;Fielding et al, 2005;Neto et al, 2013). Because cleavage often takes place at one side of the midbody (also known as asymmetric abscission), the vesicles appear to be recruited to the cleavage site of one of the daughter cells (Gromley et al, 2005;Schiel et al, 2013).…”

Sec5, a member of the exocyst complex, mediatesDrosophilaembryo cellularization

“…The vesicle-associated GTPase Sec4p binds to the exocyst protein Sec15p, potentially linking vesicles to the complex and thereby to the fusion site (Guo et al, 1999). In higher organisms, the exocyst has also been shown to be required for late stages of cytokinesis (Cascone et al, 2008;Chen et al, 2006;Fielding et al, 2005;Gromley et al, 2005). Additionally, the exocyst complex defines areas of membrane addition in neuronal growth cones and developing Drosophila oocytes (Dupraz et al, 2009;Hazuka et al, 1999;Murthy and Schwarz, 2004).…”

The regulation of abscission by multi-protein complexes

“…These data are further supported by functional interactions between exocyst components and proteins known to regulate abscission. For example, RalA and RalB interact with Sec5 and Exo84, respectively (Cascone et al, 2008;Chen et al, 2006). The interaction of RalB and Exo84 induces the assembly of a complex of beclin and the mammalian phosphatidylinositol 3-kinase Vps34 on nascent autophagosomes (Bodemann et al, 2011), which is potentially important for cytokinesis, because beclin and Vps34 are also implicated in this process (Sagona et al, 2010;Thoresen et al, 2010).…”