Rabring7, a Novel Rab7 Target Protein with a RING Finger Motif

Abstract

Rab7, a member of the Rab family small G proteins, has been shown to regulate intracellular vesicle traffic to late endosome/lysosome and lysosome biogenesis, but the exact roles of Rab7 are still undetermined. Accumulating evidence suggests that each Rab protein has multiple target proteins that function in the exocytic/endocytic pathway. We have isolated a new Rab7 target protein, Rabring7 (Rab7-interacting RING finger protein), using a CytoTrap system. It contains an H2 type RING finger motif at the C termini. Rabring7 shows no homology with RILP, which has been reported as another Rab7 target protein. GST pull-down and coimmunoprecipitation assays demonstrate that Rabring7 specifically binds the GTP-bound form of Rab7 at the N-terminal portion. Rabring7 is found mainly in the cytosol and is recruited efficiently to late endosomes/lysosomes by the GTP-bound form of Rab7 in BHK cells. Overexpression of Rabring7 not only affects epidermal growth factor degradation but also causes the perinuclear aggregation of lysosomes, in which the accumulation of the acidotropic probe LysoTracker is remarkably enhanced. These results suggest that Rabring7 plays crucial roles as a Rab7 target protein in vesicle traffic to late endosome/lysosome and lysosome biogenesis

A Retromerlike Complex Is a Novel Rab7 Effector That Is Involved in the Transport of the Virulence Factor Cysteine Protease in the Enteric Protozoan ParasiteEntamoeba histolytica

“…In contrast, overexpression of the dominant negative GDP-locked Rab7 caused diffusion of lysosomes to the periphery of the cells and decrease of EGF and LDL degradation (Bucci et al, 2000). Similar effects were also observed in overexpression of Rab7 effectors, i.e., rabinteracting lysosomal protein (RILP; Cantalupo et al, 2001) and Rab7-interacting RING finger protein (Rabring7; Mizuno et al, 2003). In contrast to mammalian Rab7, which is mainly associated with the acidic compartment (Bucci et al, 2000), Ͻ50% of GFP-EhRab7A-positive vacuoles were Lysotracker positive ( Figure 1A), suggesting that EhRab7A is not primarily localized to late endosomes or lysosomes.…”

“…This EhRab7A/ EhVps26-expressing transformant showed normal morphology of lysosomes and a total acidity as measured with a Lysotracker staining (unpublished data). In mammalian cells, the GTP-Rab7 overexpression did not influence the EGF degradation, whereas RILP and Rabring7 caused accumulation of lysosomes but showed reverse effects on EGF degradation (Bucci et al, 2000;Cantalupo et al, 2001;Mizuno et al, 2003). Quantitative immunoblot analysis of CP1, 2, and 5 in these transformants with specific antibodies showed that the amount of these CP proteins was slightly, but not significantly, reduced in EhRab7A-overexpressing transformant (unpublished data).…”

“…Homology-based genome-wide search of the putative effectors of the amoebic Rab7A using known Rab7 effectors from other organisms, including RILP, Rabring7, hVps34p/p150 (phosphatidylinositol 3-kinase), and proteasome ␣-subunit (XAPC7) indicated that this organism possesses homologues for Vps34/p150 and XAPC7, but lacks RILP and Rabring7, suggestive of the presence of novel Rab7 effectors in this organism (Cantalupo et al, 2001;Mizuno et al, 2003;Stein et al, 2003;Dong et al, 2004). Thus, we attempted to isolate the effector molecules of EhRab7A by affinity purification to gain an insight in the regulation of the amoebic Rab7A.…”

“…RILP is a soluble protein containing two coiled-coil regions and recruited on late endosomal and lysosomal membranes by Rab7-GTP and then in turn bridges phagosomes with dynein-dinactin, a microtubule-associated motor complex to associate with late endosomes and lysosomes (Harrison et al, 2003). Rabring7 is a soluble, ring finger-containing protein and also contributes to microtubule-mediated lysosomal movement (Mizuno et al, 2003). E. histolytica apparently lacks these two effectors, which is consistent with the fact that tubulins and microtubules in E. histolytica are significantly different from other organisms (Roy and Lohia, 2004;Vayssie et al, 2004), and may suggest that vesicular trafficking in E. histolytica depends on microtubule-independent Figure 5.…”

The Oxysterol-binding Protein Homologue ORP1L Interacts with Rab7 and Alters Functional Properties of Late Endocytic Compartments

“…The present finding is consistent with this and shows that, even though the clustering of LEs induced by ORP1L, ANK, and ANKϩPHD is not fully reversed by microtubule dissociation, the large clusters in the juxtanuclear region are microtubule dependent. Other Rab7 binding partners identified so far include RILP, a protein that links Rab7-positive LEs to microtubule-dependent dynein/dynactin motor complexes and has strong effects on LE/lysosomal transport (Cantalupo et al, 2001;Jordens et al, 2001); Rabring7, which affects epidermal growth factor degradation and causes perinuclear aggregation of lysosomes (Mizuno et al, 2003); and the phosphatidylinositol 3Ј-kinase VPS34 and its adaptor protein p150 (Stein et al, 2003). The clustering of LEs/lysosomes induced by ORP1L and its ANK and ANKϩPHD fragments resembles the effects of RILP or Rabring7 overexpression or that of Rab7 itself (Bucci et al, 2000).…”