Growth-regulated Hsp70 phosphorylation regulates stress responses and prion maintenance

Abstract

Maintenance of protein homeostasis in eukaryotes during normal growth and stress conditions requires the functions of Hsp70 chaperones and associated co-chaperones.Here we investigate an evolutionarily-conserved serine phosphorylation that occurs at the site of communication between the nucleotide-binding and substrate-binding domains of Hsp70. Ser151 phosphorylation in yeast Hsp70 (Ssa1) is promoted by cyclindependent kinase (Cdk1) during normal growth and dramatically affects heat shock responses, a function conserved with Hsc70 S153 phosphorylation in human cells.Phospho-mimic forms of Ssa1 (S151D) also fail to relocalize in response to starvation conditions, do not associate in vivo with Hsp40 co-chaperones, Ydj1 and Sis1, and do not catalyze refolding of denatured proteins in vitro in cooperation with Ydj1 and Hsp104. S151 phosphorylation strongly promotes survival of heavy metal exposure and reduces Sup35-dependent [PSI + ] prion activity, however, consistent with proposed roles for Ssa1 and Hsp104 in generating self-nucleating seeds of misfolded proteins. Taken together, these results suggest that Cdk1 downregulates Hsp70 function during periods of active growth, reducing propagation of aggregated proteins despite potential costs to overall chaperone efficiency.3

Comparative proteomics analysis of Shiraia bambusicola revealed a variety of regulatory systems on conidiospore formation

“…HSP70 multi-domain protein levels were very low in the mycelia of S. bambusicola but significantly increased during conidial formation. As a non-specific protective protein, HSP70 can help denatured proteins restore their correct conformation, facilitate the folding and assembly process of nascent peptide chains, and significantly improve the resistance of cells to stress (Kao et al, 2020). The differential proteins were also concentrated in the endocytic patch.…”

Closest horizons of Hsp70 engagement to manage neurodegeneration

“…Although the activity of Hsp70 is firstly dependent on its expression, some enzymes also may introduce modifications, regulating Hsp70 in kinase dependent manner. For instance, it has been reported that cyclin-dependent kinase 1 (Cdk1) is able to temporarily downregulate chaperonic functions of Hsp70 by phosphorylation of serine in a region between ATP-and substrate-binding domains (Kao et al, 2020). Interestingly, in addition to de novo synthesis of Hsp70, neurons tend to uptake it from neighboring astrocytes (Tytell et al, 1986;Hightower and Guidon, 1989;Guzhova et al, 1998Guzhova et al, , 2001Kalmar and Greensmith, 2017).…”