The Chaperone-Mediated Autophagy Receptor Organizes in Dynamic Protein Complexes at the Lysosomal Membrane

Abstract

Chaperone-mediated autophagy (CMA) is a selective type of autophagy by which specific cytosolic proteins are sent to lysosomes for degradation. Substrate proteins bind to the lysosomal membrane through the lysosome-associated membrane protein type 2A (LAMP-2A), one of the three splice variants of the lamp2 gene, and this binding is limiting for their degradation via CMA. However, the mechanisms of substrate binding and uptake remain unknown. We report here that LAMP-2A organizes at the lysosomal membrane into protein complexes of different sizes. The assembly and disassembly of these complexes are a very dynamic process directly related to CMA activity. Substrate proteins only bind to monomeric LAMP-2A, while the efficient translocation of substrates requires the formation of a particular high-molecular-weight LAMP-2A complex. The two major chaperones related to CMA, hsc70 and hsp90, play critical roles in the functional dynamics of the LAMP-2A complexes at the lysosomal membrane. Thus, we have identified a novel function for hsc70 in the disassembly of LAMP-2A from these complexes, whereas the presence of lysosome-associated hsp90 is essential to preserve the stability of LAMP-2A at the lysosomal membrane.

Transcription factor NFE2L2/NRF2 modulates chaperone-mediated autophagy through the regulation of LAMP2A

“…HSPA8 delivers cargoes to the lysosome surface, where they interact with LAMP2A [4]. Then, LAMP2A multimerizes in the lysosomal membrane to form a translocation complex [5], so that unfolded substrates can enter the lysosome, assisted by lumenal HSPA8, and eventually be degraded by lysosomal proteases [6,7]. The limiting step in the whole process appears to be the availability of LAMP2A receptor at the lysosomal membrane, as lysosomal LAMP2A levels have been reported to correlate with CMA activity, and knockdown or overexpression of LAMP2A results in a decrease or increase in CMA proportional to the levels of expression [4,8].…”

Chaperone-mediated autophagy: roles in neuroprotection

“…LAMP2A exists as a monomer at the lysosomal membrane and forms a multimeric complex in association with other proteins [26] . CMA substrates first bind to monomeric LAMP2A present at the lysosomal membrane and this interaction drives LAMP2A multimerization to produce a 700-kDa complex required for the translocation of substrate into the lysosome.…”

“…CMA substrates first bind to monomeric LAMP2A present at the lysosomal membrane and this interaction drives LAMP2A multimerization to produce a 700-kDa complex required for the translocation of substrate into the lysosome. Once substrate proteins translate into the lysosomal lumen, lysosomal Hsc70 (lys-Hsc70) promotes disassembly of the LAMP2A multimerization complex to enable monomeric LAMP2A to bind to other substrates [26] . A portion of the LAMP2A may be transported into the lysosomal lumen and degraded by cathepsin A [32] .…”

“…Many other chaperones are also involved in this process, such as Hsp40, Hsp90, and Hip [25][26][27] . Although amino-acid sequence analysis shows that almost 30% of cytosolic proteins contain a KFERQ-like sequence, only a few have been experimentally confirmed to be degraded through this process [28] .…”

Danon Disease Due to a Novel LAMP2 Microduplication

“…LAMP2's three protein products (LAMP2-A, LAMP2-B, and LAMP2-C) are integral membrane proteins, sharing a common N-terminal (luminal) domain, but with distinct transmembrane domains and cytoplasmic tails. These proteins permit the targeted import of cytoplasmic proteins (LAMP2-A, LAMP2-B) and RNA (LAMP2-C) into lysosomes for degradation (Cuervo and Dice 1996;Bandyopadhyay et al 2008;Kaushik et al 2011;Demirel et al 2012;Fujiwara et al 2013). The majority of reported Danon disease alleles are private, with nonsense and frameshift mutations predominating (Boucek et al 2011).…”