Abstract
Heat shock at 45 degrees C virtually abolishes protein synthesis in HeLa cells, but return to 37 degrees C effects a complete recovery and the concomitant synthesis of heat shock-induced proteins. Heat shock induces polysome disaggregation, indicating initiation is principally inhibited. In vitro assays for initiation factor activities reveal heat shock inhibits eukaryotic initiation factor 2 (eIF-2), eIF-(3 + 4F), and eIF-4B. Immunoblot analyses show that eIF-2 alpha and eIF-2 beta become modified during heat shock, and eIF-4B variants disappear. Upon return to 37 degrees C, these alterations reverse. The modifications of eIF-2 alpha and eIF-4B are due to phosphorylation and dephosphorylation, respectively. Enzymatic activities induced by heat shock inhibit protein synthesis and modify initiation factors in a rabbit reticulocyte lysate. Initiation factor modifications may contribute to, or cause, protein synthesis inhibition.
Highlights
Heat shock at 45 "C virtually abolishes protein synthesis in HeLa cells, but return to 37 "C effects a complete recovery and the concomitant synthesis of heat shock-induced proteins
Heat shock characteristically has two effects on translation: thepattern of protein synthesis shows the appearance of several new protein species,and the rateof protein synthesis on pre-heat shock mRNAs is inhibited
The severity of inhibition varies with cell type and determines how predominant heat shock-specific protein synthesis becomes
Summary
Heat shock induces polysome disaggregation, indicating initiation is principally inhibited. Enzymatic activities inducedby heat shock inhibit protein synthesis and modify initiation factors in a rabbit reticulocyte lysate. Initiation factor modifications may contribute to, or cause, protein synthesis inhibition. Evidence supporting an inhibition of the elongation [2] or of the initiation [3] process has been reported,as well as alterations affecting ribosomal protein S6 [4, 5], histones [5, 6] eIF1-2a [7], and ribosome activity [8, 9]. Wehave used thesemethodsto examine whether the heasthock-induced inhibition of translation in HeLacells is due to initiation factor protein alterations. The resultsclearly indicated thatmodifications of initiation factor proteins arecaused by heat shock, and suggest that some or all of the modifications contribute to the inhibition of translation
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