Variant‐specific and reciprocal Hsp40 functions in Hsp104‐mediated prion elimination

Abstract

SummaryThe amyloid‐based prions of Saccharomyces cerevisiae are heritable aggregates of misfolded proteins, passed to daughter cells following fragmentation by molecular chaperones including the J‐protein Sis1, Hsp70 and Hsp104. Overexpression of Hsp104 efficiently cures cell populations of the prion [PSI +] by an alternative Sis1‐dependent mechanism that is currently the subject of significant debate. Here, we broadly investigate the role of J‐proteins in this process by determining the impact of amyloid polymorphisms (prion variants) on the ability of well‐studied Sis1 constructs to compensate for Sis1 and ask whether any other S. cerevisiae cytosolic J‐proteins are also required for this process. Our comprehensive screen, examining all 13 members of the yeast cytosolic/nuclear J‐protein complement, uncovered significant variant‐dependent genetic evidence for a role of Apj1 (antiprion DnaJ) in this process. For strong, but not weak [PSI +] variants, depletion of Apj1 inhibits Hsp104‐mediated curing. Overexpression of either Apj1 or Sis1 enhances curing, while overexpression of Ydj1 completely blocks it. We also demonstrated that Sis1 was the only J‐protein necessary for the propagation of at least two weak [PSI +] variants and no J‐protein alteration, or even combination of alterations, affected the curing of weak [PSI +] variants, suggesting the possibility of biochemically distinct, variant‐specific Hsp104‐mediated curing mechanisms.

Three J-proteins impact Hsp104-mediated variant-specific prion elimination: a new critical role for a low-complexity domain

“…Both of these orthologs also propagate at least some variants of the prion [RNQ + ] (Lopez et al 2003). It is worth noting that Sis1 orthologs have retained the ability to propagate some variants of [PSI + ] and [RNQ + ], but all higher eukaryotic orthologs examined to date lack the ability to substitute for Sis1 in Hsp104-mediated curing, now including human Hdj1 (Sporn and Hines 2015), D. melanogaster Droj1 (Astor et al 2018), A. thaliana atDjB1 (Verma et al 2017), and five other A. thaliana Sis1 orthologs (Sahi and Hines, unpublished observations). Wickner et al, have described Hsp104-mediated curing as one of many "anti-prion" functions of yeast (Wickner et al 2015(Wickner et al , 2018.…”

“…The mechanism of Hsp104-mediated elimination of [PSI + ] is the subject of significant current debate as several contradictory models have been proposed in the recent literature (Helsen and Glover 2012;Winkler et al 2012;Park et al 2014;Zhao et al 2017;Ness et al 2017;Cox and Tuite 2018;Matveenko et al 2018). Here, we will revisit our recent findings (Astor et al 2018) and present some additional data on the roles of J-proteins in Hsp104-mediated elimination of [PSI + ]. Considering our new findings, we expand on our understanding of the role of Apj1 in this process and underscore the importance of low-complexity regions in prion biology.…”

“…Hdj1 is also sufficient in substituting for Sis1 in the propagation of strong, but not weak variants of [PSI + ] (Harris et al 2014), although it is insufficient in Hsp104-mediated elimination of [PSI + ] (Sporn and Hines 2015). In continuing this line of investigation, we recently showed that the Sis1 Drosophila melanogaster ortholog Droj1 supports the propagation of strong, but not weak [PSI + ] variants, and like Hdj1, Droj1 was also deficient in supporting Hsp104mediated [PSI + ] elimination (Astor et al 2018).…”

“…We then utilized this same set of J-protein deletion strains to determine if any of these 12 other J-proteins are required for efficient Hsp104-mediated [PSI + ] elimination. This screen revealed that in addition to Sis1, Apj1 is also required for efficient Hsp104mediated curing, but only for the strong variants; no evidence was uncovered that any J-protein, including Sis1, is necessary for the elimination of weak [PSI + ] variants (Astor et al 2018).…”

Forms and abundance of chaperone proteins influence yeast prion variant competition

“…). Interestingly, Sis1 overexpression was reported to enhance [ PSI + ] curing with excess Hsp104 (Kirkland et al ., ; Kryndushkin et al ., ; Astor et al ., ). It is plausible that fewer propagons resulted from Sis1 overexpression lowered the threshold for efficient prion elimination.…”