Role of rRAB22b, an oligodendrocyte protein, in regulation of transport of vesicles from trans Golgi to endocytic compartments

Abstract

Intracellular membrane trafficking plays an essential role in the biogenesis and maintenance of myelin. Members of the Rab protein family are important components of the systems that regulate intracellular vesicle transport. We examine the function of rRab22b, a novel rat Rab protein cloned from an oligodendrocyte cDNA library, by visualizing and identifying in living Hela cells the organelles that contain rRab22b. Our results show that rRab22b is present in the trans Golgi/TGN and endocytic compartments. Trafficking of membranes from trans Golgi to endocytic compartments takes place via small tubulo vesicular organelles containing rRab22b. The formation of vesicles in the trans Golgi also appears to be regulated by rRab22b. Additionally, our results suggest that rRab22b controls the transport of vesi-cles from the trans Golgi to endocytic compartments that localize in oligodendrocyte processes. That rRab22b is involved in the transport of certain proteins from trans Golgi to myelin is suggested by the evidence that certain proteins being targeted to the plasma membrane are first transported from trans Golgi to endocytic compartments.

Transport of mannose-6-phosphate receptors from the trans-Golgi network to endosomes requires Rab31

“…Rab31 partially co-localized with both early endosomal markers Rab5 and endocytosed transferrin (after incubation of cells for 5 min with Texas Red transferrin) [12]. The presence of Rab31 in TGN and early endosomes was recently corroborated by two other groups [14,15].…”

“…A novel Rab protein we cloned from a rat oligodendrocyte cDNA library was designated rRab22b, because of its similarity to human Rab22b [12]. Its high degree of homology, ninety six percent, with human Rab22b indicates that rRab22b is the orthologue of human Rab22b.…”

Overexpression of Rab22a hampers the transport between endosomes and the Golgi apparatus

“…However, the prominent effect of Rab22a in the trafficking between endosomes and the Golgi cisternae may cause alterations in this organelle in other cell lines. It is worth mentioning that Rab22b has been implicated in the transport from the trans-Golgi to endocytic compartments in HeLa cells and oligodendrocytes [29].…”

Polarity Development in Oligodendrocytes: Sorting and Trafficking of Myelin Components

“…Particularly abundant are rab proteins important for endosomal trafficking, such as rab5 isoforms (transport to early endosomes, early endosome fusion; Huber et al 1994;Burcelin et al 1997;Bouverat et al 2000), rab7 (transport from early to late endosomes; Burcelin et al 1997), and rab11 (transport through recycling endosomes; Huber et al 1994). Of particular interest are the OLG-specific rab22b and rab40c as their expression is increased during OLG differentiation (Rodriguez-Gabin et al 2001;RodriguezGabin et al 2004). Both proteins are localized at endosomes further supporting the importance of the endosomal system for vesicular trafficking in OLGs.…”