Chaperone Hsp27 inhibits translation during heat shock by binding eIF4G and facilitating dissociation of cap-initiation complexes

Abstract

Inhibition of protein synthesis during heat shock limits accumulation of unfolded proteins that might damage eukaryotic cells. We demonstrate that chaperone Hsp27 is a heat shock-induced inhibitor of cellular protein synthesis. Translation of most mRNAs requires formation of a cap-binding initiation complex known as eIF4F, consisting of factors eIF4E, eIF4A, eIF4E kinase Mnk1, poly(A)-binding protein, and adaptor protein eIF4G. Hsp27 specifically bound eIF4G during heat shock, preventing assembly of the cap-initiation/eIF4F complex and trapping eIF4G in insoluble heat shock granules. eIF4G is a specific target of Hsp27, as eIF4E, eIF4A, Mnk1, poly(A)-binding protein, eIF4B, and eIF3 were not bound by Hsp27 and were not recruited into insoluble complexes. Dissociation of eIF4F was enhanced during heat shock by ectopic overexpression of Hsp25, the murine homolog of human Hsp27. Overexpression of Hsc70, a constitutive homolog of Hsp70, prevented loss of cap-initiation complexes and maintained eIF4G solubility. Purified Hsp27 specifically bound purified eIF4G in vitro, prevented in vitro translation, eliminated eIF4G interaction with protein binding factors, and promoted eIF4G insolubilization. These results therefore demonstrate that Hsp27 is a heat-induced inhibitor of eIF4F-dependent mRNA translation.

HAX1-dependent control of mitochondrial proteostasis governs neutrophil granulocyte differentiation

“…Since RC-I dysfunction is not the causative mechanism for neutropenia in HAX1-deficient patients, novo" protein folding machineries, and TCA cycle (Figure 6, F and G). Notably, the group of highly enriched proteins included key RNA-binding proteins, such as MRPSs, MRPLs, and TUFM, indicative of an involvement of HSP27 in translation (52,53).…”

Translation of the ERM-1 membrane-binding domain directserm-1mRNA localization to the plasma membrane in theC. elegansembryo

“…As a complementary approach to disrupting global translation initiation via RNAi, we next disrupted translation through heat shock and quantified the resulting changes in erm-1 mRNA enrichment at the plasma membrane (Parker et al, 2020). Heat shock prevents protein synthesis primarily through changes in phosphorylation states of translation initiation factors followed by their subsequent inactivation (Cuesta et al, 2000; Duncan and Hershey, 1984; Shalgi et al, 2013). Heat shock acts within a shorter time frame than ifg-1 RNAi (25 minutes heat shock vs. 48 hrs RNAi exposure).…”

The Absence of Heat Shock Protein HSP101 Affects the Proteome of Mature and Germinating Maize Embryos

“…More recent work determined that HSC70, HSP40, eIF4F, and PABP stabilize the ARE-mRNA BIM, preventing its degradation, thereby regulating the expression of BIM, an activator of cell death in hematopoietic progenitor cells to control the number of blood cells . HSP27, a small heat shock protein, has been involved in translation inhibition by preventing eIF4F assembly under thermal shock conditions through binding and sequestering eIF4G in insoluble heat stress granules . In addition, wheat HSP101 has the ability to enhance translation of mRNAs carrying particular sequences at their 5′UTR …”

“…The second-dimension SDS-PAGE was performed in a Ettan DALT 12 System (GE Healthcare) until the dye migrated off the gel. Following SDS-PAGE, gels were fixed with 50% methanol for 30 min and, then, stained with Coomassie Colloidal (20% [v/v] ethanol, 1.6% [v/v] phosphoric acid, 8% [w/v] ammonium sulfate, 0.08% [w/v] Coomassie Brilliant Blue G-250) for at least 16 h. For S 35 -labeling analysis, after destaining, the gels were impregnated with Amplify, dried and exposed to an amplifier phosphor screen (GE Healthcare).…”