Rab6 Regulates Transport and Targeting of Exocytotic Carriers
ABSTRACT Constitutive exocytosis delivers newly synthesized proteins, lipids, and other molecules from the Golgi apparatus to the cell surface. This process is mediated by vesicles, which bud off the trans-Golgi network, move along cytoskeletal filaments, and fuse with the plasma membrane. Here, we show that the small GTPase Rab6 marks exocytotic vesicles and, together with the microtubule plus-end-directed motor kinesin-1, stimulates their processive microtubule-based transport to the cell periphery. Furthermore, Rab6 directs targeting of secretory vesicles to plasma-membrane sites enriched in the cortical protein ELKS, a known Rab6 binding partner. Our data demonstrate that although Rab6 is not essential for secretion, it controls the organization of exocytosis within the cellular space.
- SourceAvailable from: Tomasz Proszynski
- "Novel, genetically engineered sensors of protease activity may help us understand how different proteases cooperate in time to remodel the postsynaptic machinery (Stawarski et al., 2014). Another interesting issue is whether the LL5␤/ELKS complex that was recently shown to be associated with podosomes in different cell types, including cultured myotubes, could be involved in the regulation of exocytosis at synaptic podosomes, similar to its involvement in HeLa cells, and, if so, what cargo is transported in the LL5␤ exocytic pathway (Grigoriev et al., 2007; Hotta et al., 2010; Lansbergen et al., 2006; Proszynski and Sanes, 2013). Podosomeassociated proteases, adhesion molecules, and components of the ECM are all potential candidates. "
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- "Although two individuals with mutations in CC1 displayed upper motor neuron features, upper motor neuron involvement appears to be more common in families with mutations in CC2. The mutations in CC2 are found in the region that can interact with kinesin 1 (Grigoriev et al., 2007) but outside the region that is sufficient to bind the dynein-dynactin complex (Splinter et al., 2012) (Fig. 1). It is therefore possible that altered interactions of BICD2 with kinesin 1 are associated with upper motor neuron defects. "
ABSTRACT: Spinal muscular atrophy is a disorder of lower motor neurons, most commonly caused by recessive mutations in SMN1 on chromosome 5q. Cases without SMN1 mutations are subclassified according to phenotype. Spinal muscular atrophy, lower ex- tremity-predominant, is characterized by lower limb muscle weakness and wasting, associated with reduced numbers of lumbar motor neurons and is caused by mutations in DYNC1H1, which encodes a microtubule motor protein in the dynein-dynactin complex and one of its cargo adaptors, BICD2. We have now identified 32 patients with BICD2 mutations from nine different families, providing detailed insights into the clinical phenotype and natural history of BICD2 disease. BICD2 spinal muscular atrophy, lower extremity predominant most commonly presents with delayed motor milestones and ankle contractures. Additional features at presentation include arthrogryposis and congenital dislocation of the hips. In all affected individuals, weakness and wasting is lower-limb predominant, and typically involves both proximal and distal muscle groups. There is no evidence of sensory nerve involvement. Upper motor neuron signs are a prominent feature in a subset of individuals, including one family with exclusively adult-onset upper motor neuron features, consistent with a diagnosis of hereditary spastic paraplegia. In all cohort members, lower motor neuron features were static or only slowly progressive, and the majority remained ambulant throughout life. Muscle MRI in six individuals showed a common pattern of muscle involvement with fat deposition in most thigh muscles, but sparing of the adductors and semitendinosus. Muscle pathology findings were highly variable and included pseudomyopathic features, neuropathic features, and minimal change. The six causative mutations, including one not previously reported, result in amino acid changes within all three coiled-coil domains of the BICD2 protein, and include a possible ‘hot spot’ mutation, p.Ser107Leu present in four families. We used the recently solved crystal structure of a highly conserved region of the Drosophila orthologue of BICD2 to further-explore how the p.Glu774Gly substitution inhibits the binding of BICD2 to Rab6. Overall, the features of BICD2 spinal muscular atrophy, lower extremity predominant are consistent with a pathological process that prefer- entially affects lumbar lower motor neurons, with or without additional upper motor neuron involvement. Defining the phenotypic features in this, the largest BICD2 disease cohort reported to date, will facilitate focused genetic testing and filtering of next generation sequencing-derived variants in cases with similar features.Brain 02/2015; DOI:10.1093/brain/awu356 · 10.23 Impact Factor
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- "Both myosin motors and the actin cytoskeleton are key regulators of fission during vesicle formation (Miserey-Lenkei et al., 2010; Liu et al., 2013; Valente et al., 2010). Similarly, a kinesin-1 motor complex has been reported to be required for tubulation during vesicle formation in addition to its conventional role in vesicle transport (Grigoriev et al., 2007). It should be noted that JIP4, which is recruited to recycling endosomes by Rab36, functions as a scaffold protein for kinesin-1 (Montagnac et al., 2009). "
ABSTRACT: Small GTPase Rab35 is an important molecular switch for endocytic recycling that regulates various cellular processes, including cytokinesis, cell migration, and neurite outgrowth. We previously showed that active Rab35 promotes nerve growth factor (NGF)-induced neurite outgrowth of PC12 cells by recruiting MICAL-L1, a multiple Rab-binding protein, to Arf6-positive recycling endosomes. However, the physiological significance of the multiple Rab-binding ability of MICAL-L1 during neurite outgrowth remained completely unknown. Here we report that Rab35 and MICAL-L1 promote the recruitment of Rab8, Rab13, and Rab36 to Arf6-positive recycling endosomes during neurite outgrowth. We found that Rab35 functions as a master Rab that determines the intracellular localization of MICAL-L1, which in turn functions as a scaffold for Rab8, Rab13, and Rab36. We further showed by functional ablation experiments that each of these downstream Rabs regulates neurite outgrowth in a non-redundant manner downstream of Rab35 and MICAL-L1, e.g. by showing that knockdown of Rab36 inhibited recruitment of Rab36-specific effector JIP4 to Arf6-positive recycling endosomes, and caused inhibition of neurite outgrowth without affecting accumulation of Rab8 and Rab13 in the same Arf6-positive area. Our findings suggest the existence of a novel mechanism that recruits multiple Rab proteins at the Arf6-positive compartment by MICAL-L1.Biology Open 08/2014; 3(9). DOI:10.1242/bio.20148771 · 2.42 Impact Factor