ARD1-mediated Hsp70 acetylation balances stress-induced protein refolding and degradation

Abstract

Heat shock protein (Hsp)70 is a molecular chaperone that maintains protein homoeostasis during cellular stress through two opposing mechanisms: protein refolding and degradation. However, the mechanisms by which Hsp70 balances these opposing functions under stress conditions remain unknown. Here, we demonstrate that Hsp70 preferentially facilitates protein refolding after stress, gradually switching to protein degradation via a mechanism dependent on ARD1-mediated Hsp70 acetylation. During the early stress response, Hsp70 is immediately acetylated by ARD1 at K77, and the acetylated Hsp70 binds to the co-chaperone Hop to allow protein refolding. Thereafter, Hsp70 is deacetylated and binds to the ubiquitin ligase protein CHIP to complete protein degradation during later stages. This switch is required for the maintenance of protein homoeostasis and ultimately rescues cells from stress-induced cell death in vitro and in vivo. Therefore, ARD1-mediated Hsp70 acetylation is a regulatory mechanism that temporally balances protein refolding/degradation in response to stress.

Co-translational, Post-translational, and Non-catalytic Roles of N-Terminal Acetyltransferases

“…Heat shock protein 70 (Hsp70) works to promote protein refolding during the immediate time after chemical stress. NAA10 is also involved in stress response through Nε acetylation of Hsp70, increasing the affinity of Hsp70 for a co-chaperone, promoting its refolding activity (Seo et al, 2016). Further, NAA10 interacts with and Nε-acetylates the androgen receptor (AR), a mechanistic explanation for the fact that NAA10 is upregulated in prostate cancer.…”

“…Because NAA10 potentially has many modes of action, as discussed earlier, the interpretation of the exact substrates and signaling pathways through which it affects cancer cells is complicated. This ranges from its major role in the NatA complex as a NAT (Arnesen et al, 2006c;Gromyko et al, 2010) to various KAT activities toward specific substrates (Lee et al, 2017b;Lim et al, 2006;Qian et al, 2017;Seo et al, 2016;Shin et al, 2009Shin et al, , 2014Vo et al, 2017;Wang et al, 2012;Yoon et al, 2014) and non-catalytic roles (Hua et al, 2011;Lee et al, 2017a). The cancer relevance of the KAT and non-catalytic roles of NAA10 are increasingly underpinned.…”

Dynamics-function relationship of N-terminal acetyltransferases: the β6β7 loop modulates substrate accessibility to the catalytic site

“…β-hairpin loops are known to have a strong hydrophobic core and interstrand interactions keeping them compact and the turn stable [76]. The human Naa10 has been shown to acetylate internal lysines of various proteins [24,26,27,77] and the auto-acetylation on its K136 found on the β6β7 loop could be the reason of its shift of substrate specificity towards internal lysine [78]. Acetylation of unexpected substrates might be enabled by an increased mobility of loop β6β7 triggered by either a particular substrate or experimental conditions.…”

“…The loops have been proposed to prevent the access of internal lysine to the catalytic site and as a consequence prevent their acetylation by NATs [15,20]. However, there have been reports of lysine acetylations by NATs [18,21–27]. Moreover, NATs can be inhibited by so-called bisubstrate inhibitors consisting of a short polypeptide covalently bound to the Ac-CoA [6,17,28,29].…”

Unconventional Approaches to Modulating the Immunogenicity of Tumor Cells

“…Hyperacetylation of HSP90 has been proposed to cause the release of the cochaperone complex protein p23, and to inhibit the chaperone’s ATPase function, collectively reducing HSP90 chaperoning activity (Bali, Pranpat, Bradner, et al, 2005; Kekatpure, Dannenberg, & Subbaramaiah, 2009; Koga et al, 2006; Rao et al, 2008). Other chaperone proteins, e.g., HSP70 and GRP78 have also been found to be regulated by reversible acetylation (Chang et al, 2016; Li, Li, et al, 2016; Li, Zhuang, et al, 2016; Park, Seo, Park, Lee, & Kim, 2017; Seo et al, 2016). Acetylation of HSP90 has been proposed to regulate it and its client proteins ubiquitination and subsequent proteolytic breakdown (Mollapour & Neckers, 2012; Nanduri, Hao, Fitzpatrick, & Yao, 2015; Quadroni, Potts, & Waridel, 2015; Zhou, Agoston, Atadja, Nelson, & Davidson, 2008).…”