Temperature and animal cell protein synthesis.
A predominant feature of brief heat stress to animal cells is the vigorous but transient activation of a small number of specific genes, previously either silent, or active at low levels. New mRNAs are actively transcribed from these genes and are translated into proteins, known collectively as the heat shock proteins, or hsps. The number of different types of hsp varies considerably in different organisms and cell types but in all cases proteins of approximately 84 and 70 kDa are amongst the most prominent. A dramatic feature that emerges from a study of their genes is that these proteins have been highly conserved during evolution. Gene sequence data reveal specific nucleotide sequences upstream of the transcription start sites that are essential for induction. These are known as 'heat shock elements' and are believed to be the region to which activated 'heat shock transcription factors' bind to facilitate hsp gene transcription. A recent model suggests that transcriptional regulation is based on competition between abnormal intracellular proteins and such a labile regulatory factor. Other experiments suggest such hsp inducers as heat, ethanol, arsenite, or oxygenation after anoxia, may cause protein damage through oxygen-derived free radical action. Although heat shock can cause very considerable changes in transcriptional patterns, effects specifically on translational control are no less dramatic. Different organisms achieve a rapid change in different ways. In Drosophila, heat shock promotes the translation of hsp mRNAs. In yeast there is no mechanism for sequestering pre-existing mRNAs from translation. Instead these mRNAs simply disappear rapidly from the cell. Mammalian cells are different in yet another way. There is neither sequestration of pre-existing mRNAs nor their removal from the cell. Superimposed upon the transient heat induced activation of hsp genes there are now clear indications of developmental regulation. The mechanism for the specific developmental control of hsp expression is not yet known. However, as oncogene products are known to induce hsp synthesis it may be that hsps are involved in eukaryotic growth control. Hypothermia causes loss of protein synthetic activity in cultured animal cells. No specific proteins are however induced and recovery at 37 degrees C is rapid.
Burdon
R H
RH
Department of Bioscience & Biotechnology, University of Strathclyde, Glasgow, Scotland, UK.
D000818:Animals; D002477:Cells / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000096:biosynthesis*; D006358:Hot Temperature
D006360:Heat-Shock Proteins