In contrast, vesicles are not necessary in chaperone-mediated autophagy KRX-0401 price (CMA) in which substrate proteins are identified by a cytosolic chaperone that delivers them to the surface of lysosomes for internalization through a translocation complex, formed by multimerization of the CMA receptor protein, LAMP-2A (Box 2) [3].

Macroautophagy occurs through the following sequential steps orchestrated by proteins generally known as autophagy-related proteins or Atg: • Cargo recognition: In selective macroautophagy, the material sequestered for lysosomal degradation is identified by cargo-recognizing proteins. These adaptor molecules simultaneously bind the cargo (often post-translationally modified residues) and a component of the forming autophagosome membrane (LC3). Delivery of substrates to lysosomes by chaperone-mediated autophagy (CMA) is a multi-step process. Cytosolic proteins that contain a pentapeptide motif inherent in their amino acid sequence are recognized by the chaperone hsc70 and delivered to the surface of lysosomes. In order to cross the lysosomal membrane, substrate proteins interact with the receptor protein Lysosome-Associated Membrane Protein type 2A (LAMP-2A). Binding of the substrates MAPK inhibitor to the cytosolic tail of this single-spanning membrane protein promotes multimerization of LAMP-2A and the formation of an oligomeric complex required for translocation of proteins into the lysosomal

lumen for degradation. A lysosome-resident form of hsp90 stabilizes LAMP-2A during this transition, and a second lysosome chaperone, lys-hsc70, completes substrate internalization. CMA is maximally upregulated

in response to stress (i.e. prolonged lack of nutrients, oxidative stress, and cellular insults resulting in protein damage). However, basal CMA activity is detectable in most cells. Cells compensate for loss of CMA by upregulating macroautophagy or the ubiquitin–proteasome system, but this compensation is insufficient under certain conditions, rendering CMA-incompetent cells more susceptible to stress. Interestingly, this below cross-talk among proteolytic systems is multi-directional because cells with compromised macroautophagy exhibit upregulated CMA while both macroautophagy and CMA are upregulated in response to proteasome inhibition. Most of the regulation of CMA takes place at the lysosome, where rates of substrate uptake are determined by the levels of LAMP-2A at the lysosomal membrane and of lys-hsc70 in the lumen. The ability of LAMP-2A to organize into a translocation complex is another rate-limiting step in CMA-mediated degradation. The signaling mechanisms that integrate the activating stimuli of CMA are a subject of current investigation. Most connections between autophagy and disease stem from its role in quality control of the proteome and organelles and in the maintenance of the cellular energetic balance.