Armus Is a Rac1 Effector that Inactivates Rab7 and Regulates E-Cadherin Degradation

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466

Lysosomes have been classically considered terminal degradative organelles, but in recent years they have been found to participate in many other cellular processes, including killing of intracellular pathogens, antigen presentation, plasma membrane repair, cell adhesion and migration, tumor invasion and metastasis, apoptotic cell death, metabolic signaling and gene regulation. In addition, lysosome dysfunction has been shown to underlie not only rare lysosome storage disorders but also more common diseases, such as cancer and neurodegeneration. The involvement of lysosomes in most of these processes is now known to depend on the ability of lysosomes to move throughout the cytoplasm. Here, we review recent findings on the mechanisms that mediate the motility and positioning of lysosomes, and the importance of lysosome dynamics for cell physiology and pathology.

Section: Retrograde Transportmentioning

confidence: 99%

Mechanisms and functions of lysosome positioning

Guardia

Keren-Kaplan

et al. 2016

460

466

“…The activity of small GTPases is modulated by GAPs and guanine nucleotide exchange factors (GEFs) (Fukuda, 2011). Armus has been reported as a Rab7 GAP with a putative PH domain that could mediate PI(3)P binding (Frasa et al, 2010;Lemmon, 2003). Therefore, it is possible that Armus is recruited to PI(3)P-positive structures to promote Rab7-GTP hydrolysis.…”

Section: The Rab7 Gap Armus Is a Pi(3)p-binding Proteinmentioning

confidence: 99%

“…4C). Armus subcellular localization can vary between cells but intracellular puncta are present in epithelial cells (Frasa et al, 2010). Owing to the lack of reliable antibodies for endogenous proteins, we overexpressed MycArmus and Flag-Rab7 in HeLa cells and observed that Armus and Rab7 colocalized ( Fig.…”

mentioning

confidence: 99%

Vps34 regulates Rab7 and late endocytic trafficking through recruitment of the GTPase-activating protein Armus

Jaber

Mohd-Naim

Wang

et al. 2016

The class III phosphoinositide 3-kinase (PI3K) Vps34 (also known as PIK3C3 in mammals) produces phosphatidylinositol 3-phosphate [PI (3)P] on both early and late endosome membranes to control membrane dynamics. We used Vps34-deficient cells to delineate whether Vps34 has additional roles in endocytic trafficking. In Vps34 −/− mouse embryonic fibroblasts (MEFs), transferrin recycling and EEA1 membrane localization were unaffected despite elevated Rab5-GTP levels. Strikingly, a large increase in Rab7-GTP levels, an accumulation of enlarged late endosomes, and decreased EGFR degradation were observed in Vps34-deficient cells. The hyperactivation of Rab7 in Vps34-deficient cells stemmed from the failure to recruit the Rab7 GTPase-activating protein (GAP) Armus (also known as TBC1D2), which binds to PI(3)P, to late endosomes. Protein-lipid overlay and liposome-binding assays reveal that the putative pleckstrin homology (PH) domain in Armus can directly bind to PI(3)P. Elevated Rab7-GTP led to the failure of intraluminal vesicle (ILV) formation and lysosomal maturation. Rab7 silencing and Armus overexpression alleviated the vacuolization seen in Vps34-deficient cells. Taken together, these results demonstrate that Vps34 has a previously unknown role in regulating Rab7 activity and late endosomal trafficking.

“…In Fig. 1D, the expression of the GAP domain of Armus (Armus-GAP; Armus is also known as TBC1D2A) (Frasa et al, 2010) decreased the FRET/ CFP ratio in a dose-dependent manner. The expression of both Mon1a and Ccz1 with Armus-GAP (Fig.…”

Section: Development Of a Sensor For Rab7 Activitymentioning

confidence: 99%

“…The cDNA for a GAP domain of Armus (a gift from Vania M. Braga, Imperial College, London, UK; Frasa et al, 2010) was subcloned into the pCAGGS expression vector. The cDNAs for mouse Mon1a and Ccz1 were obtained by conventional PCR techniques (Fukuda et al, 1999) and subcloned into pEGFP-C1 (Clontech, Mountain View, CA).…”

Section: Plasmidsmentioning

confidence: 99%

Mon1-Ccz1 activates Rab7 only on late endosome and dissociates from lysosome in mammalian cells

Yasuda

Morishita

Fujita

et al. 2015

Rab GTPases act as molecular switches regulating various aspects of membrane trafficking. Among them, Rab5 and Rab7 play central roles in the endolysosomal network. Although many effectors downstream of Rab7 have been elucidated, our present understanding of the mechanism regulating Rab7 activity is extremely limited. It has only recently been accepted that Mon1-Ccz1 is a Rab7 guanine nucleotide exchange factor, but the question where Mon1-Ccz1 works with Rab7 is hardly answered. To address what kind of change/switch exists in the regulatory mechanism upstream of Rab7 during the transition from late endosome to lysosome, we examined Rab7 activity in steady-state cells and EGF-induced macropinocytosis using a newly developed FRET sensor. A combination of a Rab7 sensor and confocal FRET imaging techniques revealed that the activation of Rab7 on late endosomes depends on Mon1-Ccz1 and is implicated in late endosome-lysosome fusion. In contrast, Rab7 activity on lysosomes was independent of Mon1-Ccz1 and active Rab7 played a role in perinuclear clustering of lysosomes.