Rab11-depletion results in the accumulation of immature (arrows) and abnormal (arrowheads) autophagosomes compared with the control cells. but even has a key role in multicellular organisms as a cytoprotective response to stress and pathological conditions (Levine and Kroemer, 2008;Mizushimaet al., 2008). Autophagy has the capacity to engulf large portions of the cytoplasm through the formation of double-membrane vesicles, calledautophagosomes. These vesicles arise from preautophagosomal structures (PAS), which are defined sites of cytoplasm, marked by a subset of autophagy-related (Atg) proteins (Mizushimaet al., 2011). Closed autophagosomes undergo a maturation process, as they subsequently fuse with endosomes and lysosomes. On autophagy induction, the Atg1 kinase complex (ULK1/2 in mammals) localizes to the PAS (Chan and Tooze, 2009;Mizushima, 2010) and together with the class III phosphatidylinositol-3-kinase (Vps34) complex initiates the phagophore nucleation and growth OT-R antagonist 2 (Funderburket al., 2010). After these events, the users of two ubiquitin-like conjugation systems are recruited to the phagophore membrane: the Atg5-12-16 complex and the phosphatidylethanolamine-conjugated Atg8a (LC3 in mammals;Geng and Klionsky, 2008). The lipid-conjugated form of Atg8a (Atg8a-II) is located on both sides of the membrane of the phagophore OT-R antagonist 2 and autophagosomes as well. While the Atg8a located on the outer membrane is usually routed for recyclization, the other portion of Atg8a becomes caught in the autolysosomal lumen and is degraded by lysosomal hydrolases. Thus Atg8a is usually a widely used marker of autophagic structures (Klionskyet al., 2012). After completion, autophagosomes can fuse with lysosomes. However, there is also growing evidence about the convergence of the autophagic route with the earlier stages of endosomal pathways. Recent studies show that autophagosomes can fuse with different populations of both early (Toozeet al., 1990;Raziet al., 2009) and late (Lucocq and Walker, 1997;Kchlet al., 2006;Filimonenkoet al., 2007) endosomes to form cross organelles calledamphisomes(Gordon and Seglen, 1988). In spite of numerous studies, many questions remained open concerning the spatial and temporal regulation of autophagosome maturation, amphisome formation, and the exact molecular mechanisms of the fusion events. As a recent review discussed, a cross-talk may exist between autophagic and endosomal processes, which likely plays an important role in the regulation of both degradative pathways (Lambet al., 2013). The users of the Rab small GTPase protein family are the main regulators of membrane trafficking and fusion events (Stenmark, 2009). The active, GTP-bound Rab proteins recruit several specific effectors to the membrane in which they are associated, thereby determining the membrane’s identity, traffic, and fusion ability. Recent studies revealed a role for any subset of Rab proteins in Rabbit Polyclonal to PDK1 (phospho-Tyr9) autophagy (Chuaet al., 2011). Rab11 was indicated to play an important role both at the early and late stages of autophagy. Recent studies found that Rab11 is usually involved in vesicle trafficking events from recycling endosomes (REs) to the phagophore during autophagosome formation (Longattiet al., 2012;Knvelsrudet al., 2013). In the mean time, previous OT-R antagonist 2 studies suggested a role for Rab11 in the maturation of autophagosomes (Faderet al., 2008;Richardset al., 2011). == RESULTS == == Rab11 is required for amphisome formation == Rab11 was previously described as a potent regulator of autophagosome maturation in cultured mammalian cells (Faderet al., 2008). To better understand the role of Rab11 OT-R antagonist 2 in autophagy, we examined the functions of this protein inDrosophila melanogaster. We analyzed whether the decrease in the level of functional Rab11 protein causes any defect upon autophagy. Using three impartial RNA interference (RNAi) lines, we observed the accumulation of small-sized Atg8a-positive dots in Rab11-depleted cells under both fed and starved conditions (Physique 1Aand Supplemental Physique S1, A, B, E, and F). Excess fat body cells overexpressing the GDP-locked dominant-negative form of Rab11 or Rab11 hypomorphic mutant clone cells showed the same phenotype (Physique S1, C, D, and F). == FIGURE 1: == Rab11 is required for autophagosome maturation. (A) Control and Rab11-depleted (green) fat body cells of L3 fedDrosophilalarvae expressing mCherry-Atg8a (reddish). Nuclei were stained using 4,6-diamidino-2-phenylindole (DAPI, blue). The mCherry-Atg8apositive dot per cell area ratio was calculated OT-R antagonist 2 as explained and compared between Rab11 RNAi and neighboring control cells using Wilcoxon’s signed-rank test (n= 21,p< 0.0001). (B) Fat body cells.