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Proteasome activities decrease during dexamethasone-induced apoptosis of thymocytes

Beyette, Jill , Mason, Grant , Murray, Rachael, Cohen, Gerald , & Rivett, A.Jennifer (1998) Proteasome activities decrease during dexamethasone-induced apoptosis of thymocytes. Biochemical Journal, 332, pp. 315-320.

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Abstract

The induction of apoptosis in thymocytes by the glucocorticoid dexamethasone was used as a model system to investigate whether there are changes in 20 S and 26 S proteasome activities during apoptosis. We observed that thymocytes contain high concentrations of proteasomes and that following treatment with dexamethasone, cell extracts showed a decrease in proteasome chymotrypsin-like activity which correlated with the degree of apoptosis observed. The decrease in chymotrypsin-like activity of 20 S and 26S proteasomes was still apparent after these complexes had been partially puri®ed from apoptotic thymocyte extracts and was therefore not due to competition resulting from a general increase in protein turnover. The trypsin-like and peptidylglutamylpeptide hydrolase activities of proteasome complexes were also observed to decrease during apoptosis, but these decreases were reversed by the inhibition of apoptosis by the caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp(OMe)-¯uoromethylketone. However, the chymotrypsin-like activity of proteasomes decreased further in the presence of the apoptosis inhibitor. Val-Ala-Asp-¯uoromethylketone was found to inhibit the chymotrypsin- and trypsin-like activity of 26 S proteasomes in .itro. The decrease in proteasome activities in apoptosis did not appear to be due to a decrease in the concentration of total cellular proteasomes. Thus, the early decreases in 20 S and 26 S proteasome activities during apoptosis appear to be due to a down-regulation of their proteolytic activities and not to a decrease in their protein concentration. These data suggest that proteasomes may be responsible, in thymocytes, for the turnover of a protein that functions as a positive regulator of apoptosis.

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ID Code: 50499
Item Type: Journal Article
ISSN: 0264-6021
Subjects: Australian and New Zealand Standard Research Classification > BIOLOGICAL SCIENCES (060000) > BIOCHEMISTRY AND CELL BIOLOGY (060100) > Enzymes (060107)
Deposited On: 24 May 2012 12:08
Last Modified: 24 May 2012 12:08

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