Basal and stress-induced Hsp70 are modulated by ataxin-3

Abstract

Regulation of basal and induced levels of hsp70 is critical for cellular homeostasis. Ataxin-3 is a deubiquitinase with several cellular functions including transcriptional regulation and maintenance of protein homeostasis. While investigating potential roles of ataxin-3 in response to cellular stress, it appeared that ataxin-3 regulated hsp70. Basal levels of hsp70 were lower in ataxin-3 knockout (KO) mouse brain from 2 to 63 weeks of age and hsp70 was also lower in fibroblasts from ataxin-3 KO mice. Transfecting KO cells with ataxin-3 rescued basal levels of hsp70 protein. Western blots of representative chaperones including hsp110, hsp90, hsp70, hsc70, hsp60, hsp40/hdj2, and hsp25 indicated that only hsp70 was appreciably altered in KO fibroblasts and KO mouse brain. Turnover of hsp70 protein was similar in wild-type (WT) and KO cells; however, basal hsp70 promoter reporter activity was decreased in ataxin-3 KO cells. Transfecting ataxin-3 restored hsp70 basal promoter activity in KO fibroblasts to levels of promoter activity in WT cells; however, mutations that inactivated deubiquitinase activity or the ubiquitin interacting motifs did not restore full activity to hsp70 basal promoter activity. Hsp70 protein and promoter activity were higher in WT compared to KO cells exposed to heat shock and azetidine-2-carboxylic acid, but WT and KO cells had similar levels in response to cadmium. Heat shock factor-1 had decreased levels and increased turnover in ataxin-3 KO fibroblasts. Data in this study are consistent with ataxin-3 regulating basal level of hsp70 as well as modulating hsp70 in response to a subset of cellular stresses.

Identification and analysis of HSP70 from Sepiella maindroni under stress of Vibrio harveyi and Cd 2+

“…(For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) (Wu et al, 2003), bay scallop A. irradians (Reina et al, 2012), Mytilus galloprovincialis (Anestis et al, 2007), and M. coruscus (Liu et al, 2014). In this study the complete cDNA sequence of HSP70 from S. maindroni was identified by homology cloning (GenBank accession no.…”

“…HSP70s are responsible for the folding or assembly of native proteins and extracellular immunoregulatory functions (Reina et al, 2012). The protective mechanism of HSP70 is the induction of stress response proteins as molecular chaperones involved in heat, heavy metals, desiccation, diseases and parasites (Tukaj et al, 2011).…”

Basal and stress-inducible expression of HSPA6 in human keratinocytes is regulated by negative and positive promoter regions

“…Other non-HSF proteins have also been recently shown to contribute control over basal and stress-induced HSP expression. Ataxin-3, possibly through DNA binding but more likely through its interaction with transcription factors, augments the full capacity of the HSP70 (HSPA1A) promoter to thermal and chemical stress (Reina et al 2012).…”

Toward therapeutic targets for SCA3: Insight into the role of Machado–Joseph disease protein ataxin-3 in misfolded proteins clearance

“…Ataxin-3-deficient fibroblast cells showed a clear reduction in both basal and stress-induced levels of HSP70 (Reina et al, 2012) as well as its regulator Hsf1. It seemed that lack of ataxin-3 affects transcription rather than the turnover of HSP70 in ataxin-3 knockout mice.…”