A biosensor to gauge protein homeostasis resilience differences in the nucleus compared to cytosol of mammalian cells

Abstract

An extensive network of chaperones and other proteins maintain protein homeostasis and guard against inappropriate protein aggregation that is a hallmark of neurodegenerative diseases. Using a fluorescence resonance energy-based biosensor that simultaneously reports on intact cellular chaperone holdase activity and detrimental aggregation propensity, we investigated the buffering capacity of the systems managing protein homeostasis in the nucleus of the human cell line HEK293 compared to the cytosol. We found that the nucleus showed lower net holdase activity and reduced capacity to suppress protein aggregation, suggesting that the nuclear quality control resources are less effective compared to those in the cytosol. Aggregation of mutant huntingtin exon 1 protein (Httex1) in the cytosol appeared to deplete cytosolic chaperone supply by depleting holdase activity.