Proteasome Failure Promotes Positioning of Lysosomes around the Aggresome via Local Block of Microtubule-Dependent Transport

Abstract

bUbiquitinated proteins aggregate upon proteasome failure, and the aggregates are transported to the aggresome. In aggresomes, protein aggregates are actively degraded by the autophagy-lysosome pathway, but why targeting the aggresome promotes degradation of aggregated species is currently unknown. Here we report that the important factor in this process is clustering of lysosomes around the aggresome via a novel mechanism. Proteasome inhibition causes formation of a zone around the centrosome where microtubular transport of lysosomes is suppressed, resulting in their entrapment and accumulation. Microtubule-dependent transport of other organelles, including autophagosomes, mitochondria, and endosomes, is also blocked in this entrapment zone (E-zone), while movement of organelles at the cell periphery remains unaffected. Following the whole-genome small interfering RNA (siRNA) screen for proteins involved in aggresome formation, we defined the pathway that regulates formation of the E-zone, including the Stk11 protein kinase, the Usp9x deubiquitinating enzyme, and their substrate kinase MARK4. Therefore, upon proteasome failure, targeting of aggregated proteins of the aggresome is coordinated with lysosome positioning around this body to facilitate degradation of the abnormal species.

Dynamic JUNQ inclusion bodies are asymmetrically inherited in mammalian cell lines through the asymmetric partitioning of vimentin

“…Additionally, we demonstrate that the JUNQ is asymmetrically inherited, providing a basis for further study of how damaged cellular material is partitioned during division. Direct observation of misfolded protein turnover in IBs reinforces the predictions of many studies (15,29) suggesting that inclusions are not passive by-products of protein aggregation, but rather serve an important quality-control function in the cell. Seeing JUNQ formation and maturation as a dynamic process helps to reconcile divergent observation into a coherent model.…”

“…Although IBs were suspected of mediating misfolded protein degradation due to association with ubiquitin, proteasomes, and lysosomes (21,29), little direct evidence existed for degradation within the IB, as opposed to clearance from the IB by diffusion followed by degradation elsewhere. Our 3D longitudinal experiments demonstrate protein turnover in the JUNQ.…”

The initiator caspase Dronc is subject of enhanced autophagy upon proteasome impairment in Drosophila

“…To explain the synergistic control of Dronc protein levels by the UPS and autophagy, we considered that, because the UPS and autophagy are mechanistically linked, impairment of the UPS can enhance autophagy, which is often referred to as compensatory autophagy 1,[19][20][21][22][23][24][25][26][27] (reviewed by Park and Cuervo, 3 Wojcik 28 and Lamark and Johansen 29 ). For example, in Drosophila, compensatory autophagy after proteasome impairment has been reported in neurons, in fat body cells and in adult flies.…”

“…16 The incorporation of Atg8 fusion proteins (for example, with green fluorescent protein (GFP) and/or mCherry) into autophagosomes is often used as a marker for autophagosomes 17 and autophagic flux. 18 Although it was initially assumed that the UPS and autophagy are independent of each other, recent evidence has suggested that there is crosstalk and feedback between the two 1,[19][20][21][22][23][24][25][26][27] (reviewed by Park and Cuervo, 3 Wojcik 28 and Lamark and Johansen 29 ). This is mostly due to the observation that autophagy can also degrade ubiquitylated proteins.…”

Defective recruitment of motor proteins to autophagic compartments contributes to autophagic failure in aging

“…In the case of autophagy, the balance of active motor proteins on the surface of autophagosomes has been proposed to prevent their premature or random fusion with lysosomes (Mackeh et al., 2013). In most cells, autophagosome–lysosome fusion occurs mainly in the perinuclear region where it is facilitated through both physical proximity of the organelle and slowing of vesicular trafficking (Kimura, Noda & Yoshimori, 2008; Zaarur et al., 2014). Consequently, efficient positioning of these degradative compartments in the vicinity of the nucleus in a microtubule‐dependent manner is an essential step for the final completion of the autophagic process (Kimura et al., 2008; Monastyrska et al., 2009; Sakai, Araki & Ogawa, 1989).…”