Rab5 is a key regulator of early endosomal traffic and fusion. It shares its localization and guanine nucleotide exchange factor Rabex-5 with the less characterized member of the Rab5 subfamily Rab21. Show more
Rab5 is a key regulator of early endosomal traffic and fusion. It shares its localization and guanine nucleotide exchange factor Rabex-5 with the less characterized member of the Rab5 subfamily Rab21. Here, we found that, similarly to Rab5, Rab21 also interacts with the tethering protein EEA1. Overexpression of Rab21 rescues the defects in EEA1 localization and endosomal size caused by the depletion of PI3P or the inhibition of Rab5 function, both needed for the recruitment of EEA1 to early endosomes. Interestingly, modulation of the binding properties of Rab5 or Rab21 dominant negative mutant with Rabex-5 support a model in which Rab5 and Rab21 compete for the activation by Rabex-5 and suggest that Rab21 might have higher affinity for this GEF than Rab5 Show less
Carboxypeptidases Y (Cpy1) and S (Cps1), the receptor Vps10, and the ATPase subunit Vph1 follow the carboxypeptidase Y (CPY) pathway from the trans-Golgi network (TGN) to the prevacuolar endosome (PVE Show more
Carboxypeptidases Y (Cpy1) and S (Cps1), the receptor Vps10, and the ATPase subunit Vph1 follow the carboxypeptidase Y (CPY) pathway from the trans-Golgi network (TGN) to the prevacuolar endosome (PVE). Using Schizosaccharomyces pombe quantitative live-cell imaging, biochemical and genetic analyses, we extended the previous knowledge and showed that collaboration between Gga22, the dominant Golgi-localized Gamma-ear-containing ARF-binding (GGA) protein, and Gga21, and between Gga22 and the endosomal epsin Ent3, was required for efficient: i) Vps10 anterograde trafficking from the TGN to the PVE; ii) Vps10 retrograde trafficking from the PVE to the TGN; iii) Cps1 exit from the TGN, and its sorting in the PVE en route to the vacuole; and iv) Syb1/Snc1 recycling to the plasma membrane through the PVE. Therefore, monomeric clathrin adaptors facilitated the trafficking of Vps10 in both directions of the CPY pathway, and facilitated trafficking events of Cps1 in different organelles. By contrast, they were dispensable for Vph1 trafficking. Thus, these adaptors regulated the traffic of some, but not all, of the cargo of the CPY pathway, and regulated the traffic of cargoes that do not follow this pathway. Additionally, this collaboration was required for PVE organization and efficient growth under stress. Show less