Protein aggregation can inhibit clathrin-mediated endocytosis by chaperone competition

Abstract

Protein conformational diseases exhibit complex pathologies linked to numerous molecular defects. Aggregation of a diseaseassociated protein causes the misfolding and aggregation of other proteins, but how this interferes with diverse cellular pathways is unclear. Here, we show that aggregation of neurodegenerative disease-related proteins (polyglutamine, huntingtin, ataxin-1, and superoxide dismutase-1) inhibits clathrin-mediated endocytosis (CME) in mammalian cells by aggregate-driven sequestration of the major molecular chaperone heat shock cognate protein 70 (HSC70), which is required to drive multiple steps of CME. CME suppression was also phenocopied by HSC70 RNAi depletion and could be restored by conditionally increasing HSC70 abundance. Aggregation caused dysregulated AMPA receptor internalization and also inhibited CME in primary neurons expressing mutant huntingtin, showing direct relevance of our findings to the pathology in neurodegenerative diseases. We propose that aggregateassociated chaperone competition leads to both gain-of-function and loss-of-function phenotypes as chaperones become functionally depleted from multiple clients, leading to the decline of multiple cellular processes. The inherent properties of chaperones place them at risk, contributing to the complex pathologies of protein conformational diseases.proteostasis | chaperone-dependent processes | protein misfolding | HSP70

SOD1 aggregation in ALS mice shows simplistic test tube behavior

“…The cause of neural damage in ALS is yet poorly understood, largely because of the inherent challenge of singling out a key decisive factor in the global cellular response to SOD1 aggregation. Qualified suggestions range from erroneous radical production (53), chaperone overload (54,55), and aggregate sequestration of essential proteins (56) to toxic oligomers analogous to those implicated in other neurodegenerative diseases (37,57). The results from this study add yet another possibility to put to experimental test: general aggregate overload.…”

Proteostasis impairment in protein-misfolding and -aggregation diseases

“…Inclusions disappear when huntingtin expression is blocked [108]. Multiple lines of evidence suggest that polyQ expanded proteins titrate chaperones away from their clients, leading to proteostasis impairment [44,74,100,109,110]. Conversely, overexpression of various chaperones, such as members of the Hsp70 system, suppresses polyQ toxicity [3, 69,75].…”

“…This view is supported by findings that the expression of structurally unrelated aggregation-prone proteins prevents other proteins from being proteasomally degraded. Examples include polyQ-expansion proteins, the disease- as the uncoating of clathrin cages in endocytosis [74]. Notably, due to its high degree of interconnectedness and inbuilt redundancy, the PN is robust and able to buffer the deleterious consequences of aberrant protein species for long periods of time (up to decades in humans).…”

Protein homeostasis of a metastable subproteome associated with Alzheimer’s disease

“…We also found a number of components of molecular chaperone networks coexpressed with the AD metastable subproteome (Dataset S1, Table S5). Such components include co-Hsp70/Hsp90 species, which are known to assist the Hsp70/Hsp90 system to degrade protein aggregates (70,71). Among such molecular chaperones, we found DNAJC6, a J-domain cochaperone with a role in HSC70-mediated uncoating of the clathrin-coated vesicles in neurons by recruiting HSC70.…”