Quantitative proteomics of heat-treated human cells show an across-the-board mild depletion of housekeeping proteins to massively accumulate few HSPs

Abstract

Classic semiquantitative proteomic methods have shown that all organisms respond to a mild heat shock by an apparent massive accumulation of a small set of proteins, named heat-shock proteins (HSPs) and a concomitant slowing down in the synthesis of the other proteins. Yet unexplained, the increased levels of HSP messenger RNAs (mRNAs) may exceed 100 times the ensuing relative levels of HSP proteins. We used here high-throughput quantitative proteomics and targeted mRNA quantification to estimate in human cell cultures the mass and copy numbers of the most abundant proteins that become significantly accumulated, depleted, or unchanged during and following 4 h at 41 °C, which we define as mild heat shock. This treatment caused a minor across-the-board mass loss in many housekeeping proteins, which was matched by a mass gain in a few HSPs, predominantly cytosolic HSPCs (HSP90s) and HSPA8 (HSC70). As the mRNAs of the heat-depleted proteins were not significantly degraded and less ribosomes were recruited by excess new HSP mRNAs, the mild depletion of the many housekeeping proteins during heat shock was attributed to their slower replenishment. This differential protein expression pattern was reproduced by isothermal treatments with Hsp90 inhibitors. Unexpectedly, heat-treated cells accumulated 55 times more new molecules of HSPA8 (HSC70) than of the acknowledged heat-inducible isoform HSPA1A (HSP70), implying that when expressed as net copy number differences, rather than as mere “fold change” ratios, new biologically relevant information can be extracted from quantitative proteomic data. Raw data are available via ProteomeXchange with identifier PXD001666.Electronic supplementary materialThe online version of this article (doi:10.1007/s12192-015-0583-2) contains supplementary material, which is available to authorized users.

Identification of differentially expressed reproductive and metabolic proteins in the female abalone ( Haliotis laevigata ) gonad following artificial induction of spawning

“…It is hypothesised that the lower protein abundance observed in SP gonads (compared to the PSP group) was due to a lag between mRNA transcription and protein translation as previously observed for Jurkat cells subjected to mild heat shock where protein expression peaked after three hours of heat stimulation (Finka et al, 2015). This would also explain the peak in protein expression observed in the PSP group that was collected six hours after the heat shock induced during spawning induction.…”

HSP70 in human polymorphonuclear and mononuclear leukocytes: comparison of the protein content and transcriptional activity of HSPA genes

“…On the other hand, heat shock causes an induction of a massive synthesis of HSPs to protect cells against the stress (Trotter et al 2001;Shalgi et al 2013;Finka et al 2015). Both regimes of hyperthermia used in this work induced immediate transcription of HSPA genes in granulocytes and mononuclear cells that peaked within the first hour after exposure and then greatly declined (Fig.…”

“…However, the hyperthermia-induced accumulation of Hsc70 was subsequently described for several cell types (Finka et al 2015). The authors noted that despite the lower HSPA8 extent of expression in comparison with HSPA1A/B, a copy number of newly synthesized Hsc70 molecules may greatly exceed the number of Hsp70 molecules due to an initially greater intracellular Hsc70 content that can be important for the further successful functioning of the cell.…”

“…Translation efficacy of the genes might also change with temperature increase (Finka et al 2015). To trace the hyperthermia effects, intracellular Hsp70 levels were assessed in granulocytes and mononuclear cells after both mild and severe HS.…”

Editorial: The HSP70 Molecular Chaperone Machines

“…Hence, following a 4 h mild fever-like heat-shock at 41°C, the total mass of the HSP70s in Jurkat cells increases 1.6-folds, from ~0.7% (at 37°C) to ~1.1% (Finka et al, 2015). Thus, although sharing 90% sequence identity with HSPA8, the cytosolic HSPA1A, which generally remains undetected in unstressed tissues, strongly accumulates during various abiotic stresses (Finka et al, 2015). Noticeably, non-heat-shocked cancer cells generally express constitutively abnormally elevated levels of HSPA1A that may even exceed the naturally high amounts of HSPA8.…”