Polyglutamine-Expanded Androgen Receptors Form Aggregates That Sequester Heat Shock Proteins, Proteasome Components and SRC-1, and Are Suppressed by the HDJ-2 Chaperone

Abstract

Spinal bulbar muscular atrophy is a neurodegenerative disorder caused by a polyglutamine expansion in the androgen receptor (AR). We show in transiently transfected HeLa cells that an AR containing 48 glutamines (ARQ48) accumulates in a hormone-dependent manner in both cytoplasmic and nuclear aggregates. Electron microscopy reveals both types of aggregates to have a similar ultrastructure. ARQ48 aggregates sequester mitochondria and steroid receptor coactivator 1 and stain positively for NEDD8, Hsp70, Hsp90 and HDJ-2/HSDJ. Co-expression of HDJ-2/HSDJ significantly represses aggregate formation. ARQ48 aggregates also label with antibodies recognizing the PA700 proteasome caps but not 20S core particles. These results suggest that ARQ48 accumulates due to protein misfolding and a breakdown in proteolytic processing. Furthermore, the homeostatic disturbances associated with aggregate formation may affect normal cell function.

Accumulation of Mutant Huntingtin Fragments in Aggresome-like Inclusion Bodies as a Result of Insufficient Protein Degradation

“…Cummings et al (1998) showed that ubiquitin-positive nuclear inclusions in neurons of spinocerebellar ataxia type 1 patients and transgenic mice stain positively for the 20S proteasome and the molecular chaperone HDJ-2/HSDJ, indicating that subcomplexes of the 26S proteasome as well as heat shock proteins are redistributed to the sites of ataxin-1 protein aggregation. These results were confirmed in cell culture, transgenic mouse as well as fly model systems, using different polyQ-containing proteins Stenoien et al, 1999;Warrick et al, 1999). Together these findings suggest that the redistribution of the proteasomal machinery and molecular chaperones to polyQ-containing protein aggregates is a natural response of cells to remove misfolded aggregation-prone proteins.…”

TorsinA and heat shock proteins act as molecular chaperones: suppression of α‐synuclein aggregation

“…Cummings et al (1998) used a cellular model of mutant ataxin-1 aggregation to demonstrate that HDJ-1, HDJ-2 and Hsp70 all colocalized with nuclear inclusions. A similar study found that Hsp90 colocalizes with aggregates of mutant androgen receptor but not aggregates of mutant ataxin-3, also using in vitro models of aggregation (Stenoien et al 1999). Regardless, it remains to be determined if any of the proteins deposited in Lewy bodies are related to the function of a-synuclein or are coincidental, and there is a possibility that HSPs and torsinA are unrelated to the function of a-synuclein or to the disease processes present in PD and related disorders.…”

Essential role for the dimerization domain of NuMA-RARα in its oncogenic activities and localization to NuMA sites within the nucleus

“…Cells were fed with fresh media the day after transfection and allowed to recover approximately 24 h prior to addition of vehicle (ethanol) or ATRA at a final concentration 10 À6 m for 2 h as indicated ( Figure 7). Cells were fixed as described (Stenoien et al, 1999) and imaged on LSM 510 confocal microscope (Carl Zeiss, Inc.). Representative images from single focal planes were digitally processed in an identical manner for presentation using Adobe Photoshop.…”