Title

Protein aggregation can inhibit clathrin-mediated endocytosis by chaperone competition.

Journal

Proceedings of the National Academy of Sciences of the United States of America

Volume

111

Issue

None

Pages

E1481-90

Date

2014-04-15

Authors

Shah B | Lo DC | Yu A | Shibata Y | Calamini B | Morimoto RI

However, CME was substantially reduced in cells con- taining Q82 aggregates (Fig. 1 B , arrows), with quantification of internalized transferrin fluorescence showing a 63 ± 11% reduction in aggregate-containing cells compared with cells expressing soluble Q19 or Q82 (Fig. 1 C ).

CME inhibition was also observed in cells containing aggregated forms of polyQ- expanded Htt exon 1 (Htt Q53); these cells exhibited 50 ± 15% reduced levels of internalized transferrin compared with cells with soluble Htt Q23 or Htt Q53 protein (Fig. S2 A–C ).

In contrast, there was a marked reduction in CME in neurons containing mutant Htt exon 1 Q73-CFP aggregates compared with nonexpressing cells (Fig. 5 B , Center ; quantification in Fig. 5 D );

It has been proposed that such an imbalance may trigger the onset of many neurodegenerative diseases (10, 26), and recent studies report that polyglutamine (polyQ)-based aggregates can se- quester and inhibit the function of a low-abundance cochaper- one, Sis1p/DNAJB1, in protein degradation (27).

Previous studies have shown that ag- gregation of expanded polyQ negatively affects endocytosis in yeast and in human HEK 293 cells (34).

Nevertheless, HSC70-ag- gregate colocalization reliably predicted CME inhibition.

Importantly, aggregate-driven CME inhibition is reversible and can be rescued by nominally increasing HSC70 levels.

Although internalized transferrin levels remained un- changed in cells with near-normal amounts of HSC70, cells with over a 50% reduction in HSC70 expression had significant CME inhibition (compare Fig. 2 E and D ), with a 51 ± 17% decrease in internalized transferrin fluorescence compared with nondepleted cells.

. Be- yond maintaining the general solubility of the CME machinery, HSC70 is specifically required for both the disassembly of the clathrin coat from endocytosed vesicles (20, 29 – 31) and in the recycling of coat components back to the plasma membrane.

Down- regulation of CME was not limited to polyQ-induced aggre- gation; cells with aggregated mutant SOD1 A4V also exhibited a 50 ± 10% decrease in levels of internalized transferrin com- pared with cells expressing the soluble WT or mutant protein (Fig. 1 E–G ).

Here, we show that diverse disease-associated aggregates se- quester the highly abundant major chaperone heat shock cognate protein 70 (HSC70) to the point of functional collapse of an essential cellular process, clathrin-mediated endocytosis (CME).

BEL Commons is developed and maintained in an academic capacity by Charles Tapley Hoyt and Daniel Domingo-Fernández at the Fraunhofer SCAI Department of Bioinformatics with support from the IMI project, AETIONOMY. It is built on top of PyBEL, an open source project. Please feel free to contact us here to give us feedback or report any issues. Also, see our Publishing Notes and Data Protection information.

If you find BEL Commons useful in your work, please consider citing: Hoyt, C. T., Domingo-Fernández, D., & Hofmann-Apitius, M. (2018). BEL Commons: an environment for exploration and analysis of networks encoded in Biological Expression Language. Database, 2018(3), 1–11.