Heat shock and recovery are mediated by different translational mechanisms.

Abstract

When Drosophila cells are shifted from 25°C to 37C, protein synthesis is rapidly redirected from the complex pattern characteristic of normal growth to the simple pattern of heat shock proteins (HSPs). On return to 250C, synthesis ofnormal proteins is gradually reactivated and that of HSPs is repressed.In quantifying many different recovery experiments, we found that preexisting mRNAs always behaved as a cohort, with messages for different proteins returning to translation at the same rate. Heat shock mRNAs (HS mRNAs), on the other hand, never behaved as a cohort. Their repression was asynchronous, with translation of hsp7O always the first and translation of hsp82 always the last to be repressed. Although recovery times varied enormously (depending on the severity of the heat treatment), repression of hsp7O was always correlated with restoration of normal synthesis, suggesting a link between the two events. hsp7O repression was not simply due to competition with reactivated 250C mRNAs. A general decline in the translation efficiency of hsp7O mRNA was not observed. Instead, an increasing number of messages were translationally inactivated, while those remaining in the translational pool retained full ribosome loading. Unlike inactive 25°C mRNAs, which are stable during heat shock, inactive HSP mRNAs are degraded during recovery.When eukaryotic cells are exposed to temperatures 5-15°C above their optimum for growth, they respond by inducing a small number of evolutionarily conserved proteins, the socalled heat shock proteins (HSPs). The response of Drosophila cells is particularly rapid and dramatic [see Ashburner and Bonner (1) for review]. Within minutes ofa shift from 25°C to 37°C, transcription is blocked at most previously active sites and is vigorously initiated at HS gene loci (2-4). At the same time, a mechanism oftranslational control is activated that clears preexisting messages from polysomes and allows heat shock messages to be translated with maximum efficiency as soon as they appear (5,(8)(9)(10)(11)(12)(13)(14). This response provides the most dramatic example of selective translational regulation known in any eukaryotic cell.The commitment to heat shock synthesis is not a terminal event; when cells are returned to 250C, normal patterns oftranscription and translation are gradually restored (6-8). Thus, an equally profound change in the specificity of translation occurs during recovery. We examined several parameters of recovery after subjecting cells to a variety of different heat treatments. The data indicate that the shift away from heat shock-synthesis is accomplished by a different mechanism than the shift into 'heat shock synthesis.MATERIALS cells are exposed to elevated temperatures, they shift entirely to heat shock synthesis within 20 min. This contrasts with a much more gradual restoration of normal protein synthesis when cells are returned to 25°C. Fig. 1 displays a time course of recovery following a 30-min treatment at 36.5°C, the optimum temperature for HS induction with our ...

Anaerobic treatment of maize roots affects transcription of Adh1 and transcript stability.

“…Recovery from anoxia involves a rapid decrease in Adhl transcription and decreased stability of Adhl transcripts. Similarly, recovery from heat shock involves decreased hsp transcription and decreased stability of hsp transcripts (8). We conclude that the response of maize roots to flooding is remarkably similar to the response of Drosophila cells to heat shock, involving a complex set of regulatory changes affecting both RNA production and turnover.…”

Glucocorticoid-induced glucose release is abolished in trout hepatocytes with elevated hsp70 content

“…Vijayan, Submitted). As the re-synthesis of other proteins correlates with repressed hsp70 synthesis, our results suggest that the 'normal' protein synthetic machinery in trout hepatocytes is perhaps inhibited for longer periods relative to mammalian or transformed fish cells (DiDomenico et al 1982, Kothary et al 1984. This inhibition may be due to either the intensity of the HS (+15 C) and/or the lower ambient temperature (13 C) in the present study.…”

“…These stressors induced hsp70 synthesis at 3 h of recovery and the protein accumulated over a 24 h period. While studies with transformed cells showed that HS-or arsenite-induced hsp70 synthesis is repressed upon recovery (DiDomenico et al 1982, Kothary et al 1984, we detected 35[S]methionine incorporation into hsp70 even at 24 h post-recovery from HS (A.N. Boone and M.M.…”

“…Upon exposure to stressors, particularly those affecting the protein machinery, the inducible form of hsp70 is synthesized in large amounts and is crucial for maintaining cellular homeostasis (Parsell & Lindquist 1993). Also, stressor-induced hsp70 synthesis represses the transcription and/or translation of other cellular proteins, whereas the removal of this inhibition correlates with decreased hsp70 synthesis during recovery from HS (DiDomenico et al 1982). Thus hsp70 induction, while crucial for cellular stressor tolerance and survival, may impact the metabolic potential of cells to subsequent stressors.…”

Heat shock proteins (HSPs) in coeliac disease

“…Later these puffs were found to code proteins, which were identified as HSPs (Moran et al, 1978). When eukaryotic cells were exposed to temperatures 5-15 °C above their optimum for growth, they responded also by induction of HSPs (DiDomenico et al, 1982). These molecules were found also in prokaryotes and other eukaryotes (Lemaux et al, 1978;Carper et al, 1987;Kelley & Schlesinger, 1978;Timperio et al, 2008).…”