Inhibition of Proteasomes Induces Accumulation, Phosphorylation, and Recruitment of HSP27 and   -Crystallin to Aggresomes

Abstract

Molecular chaperones and the ubiquitin-proteasome pathway are known to participate in the quality control of proteins in cells. In this study, we examined the responses of small heat shock proteins to proteasome inhibitors to clarify their roles under conditions where misfolded proteins are abnormally accumulated. HSP27 and alphaB-crystallin accumulated in both soluble and, more prominently, insoluble fractions after exposure to MG-132, a proteasome inhibitor. Enhanced expression of mRNAs for HSP27 and alphaB-crystallin was observed, suggesting transcriptional activation. Phosphorylation of HSP27 and alphaB-crystallin in cells treated with MG-132 was enhanced concomitantly with activation of p38 and p44/42 MAP kinase pathways. Immunofluorescence analysis revealed that exposure to proteasome inhibitors induced the formation of aggresomes in U373 MG cells, to which HSP27 and alphaB-crystallin were recruited. However, phosphorylation was not required for this accumulation in aggresomes. Thus, HSP27 and alphaB-crystallin are increased, phosphorylated and localized in aggresomes when proteasome activity is inhibited.

AβPP-overexpression and proteasome inhibition increase αB-crystallin in cultured human muscle: Relevance to inclusion-body myositis

“…Those cultured muscle fibers mimic the normally-appearing IBM biopsied muscle fibers that have αBC increase without "significant" morphologic abnormalities [17]. Proteasome inhibition, which appears to be an important part of the s-IBM pathogenesis and in AβPP+ CHMFs, results in aggresome formation [4], additionally increased αBC expression and, in AβPP+ CHMFs, caused αBC accumulation in aggresomes, as previously shown in human glioma cells [32]. (In our studies, increased αBC in AβPP+ CHMFs is not due to the adenovirus transfer vector because using the same vector to transfer antisense AβPP cDNA did not result in increased αBC).…”

Antitumor Activity of PR-171, a Novel Irreversible Inhibitor of the Proteasome

“…The effects of PR-171 on accumulation of these markers was more pronounced than with bortezomib, consistent with the greater effects of brief PR-171 exposure on cell viability, apoptosis, and cell cycle progression. Heat shock protein induction is a common response to cellular stress, including perturbation of proteasome function and accumulation of misfolded proteins (31,36,38,39). Both hsp27 and hsp70 were elevated at the 24-h time point in both cell lines and with both drugs, suggesting that this is a shared, but relatively delayed, response to proteasome inhibition.…”

“…The markers examined included direct proteasome substrates as well as markers that accumulate as a functional consequence of activation of apoptotic, growth arrest, or stress response pathways. Each of the markers has been previously shown to accumulate in cells treated for extended periods with proteasome inhibitors (12,31,(33)(34)(35)(36)(37). The effects of proteasome inhibition on the different markers varied by drug, cell line, and time point of analysis.…”

Proteolytic Stress Causes Heat Shock Protein Induction, Tau Ubiquitination, and the Recruitment of Ubiquitin to Tau-Positive Aggregates in Oligodendrocytes in Culture

“…HSPs can be induced by direct impairment of the proteasomal degradation pathway by proteasome inhibitors (Lee and Goldberg, 1998;Ito et al, 2002;Goldbaum et al, 2003). The present study was undertaken to elucidate whether proteasomal inhibition in cultured oligodendrocytes causes the accumulation of HSPs and ubiquitin and the formation of cytoplasmic inclusions, as observed in neurodegenerative diseases with oligodendroglial pathology.…”