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Effect of heat shock on protein degradation in mammalian cells: involvement of the ubiquitin system.
Author(s) -
Parag H.A.,
Raboy B.,
Kulka R.G.
Publication year - 1987
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1002/j.1460-2075.1987.tb04718.x
Subject(s) - ubiquitin , proteolysis , biology , heat shock protein , protein degradation , ubiquitin ligase , microbiology and biotechnology , biochemistry , enzyme , gene
Exposure of cultured rat hepatoma (HTC) cells to a 43 degrees C heat shock transiently accelerates the degradation of the long‐lived fraction of cellular proteins. The rapid phase of proteolysis which lasts approximately 2 h after temperature step‐up is followed by a slower phase of proteolysis. During the first 2 h after temperature step‐up there is a wave of ubiquitin conjugation to cellular proteins which is accompanied by a fall in ubiquitin and ubiquitinated histone 2A (uH2A) levels. Upon continued incubation at 43 degrees C the levels of ubiquitin conjugates fall with a corresponding increase of ubiquitin and uH2A to initial levels. The burst of protein degradation and ubiquitin conjugation after temperature step‐up is not affected by the inhibition of heat shock protein synthesis. Cells of the FM3A ts85 mutant, which have a thermolabile ubiquitin activating enzyme (E1), do not accelerate protein degradation in response to a 43 degrees C heat shock, whereas wild‐type FM3A mouse cells do. This observation indicates that the ubiquitin system is involved in the degradation of heat‐denatured proteins. Sequential temperature jump experiments show that the extent of proteolysis at temperatures up to 43 degrees C is related to the final temperature and not to the number of steps taken to attain it. Temperature step‐up to 45 degrees C causes the inhibition of intracellular proteolysis. We propose the following explanation of the above observations. Heat shock causes the conformational change or denaturation of a subset of proteins stable at normal temperatures.(ABSTRACT TRUNCATED AT 250 WORDS)