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Degradation of constitutive transcription factors during apoptosis in rat thymocytes
I de Belle1, L Testolin, S Pandey
1Institute for Biological Sciences, National Research Council of Canada, Ottawa, ON.
Abstract:
Dexamethasone (Dex) accelerates the rate of apoptosis in thymocytes by a process thought to require gene expression. Among the genes implicated in the regulation of this phenomenon are the immediate early genes such as c-fos and c-jun, whose expression is modulated by a complement of preexisting transcription factors. We have analyzed the DNA-binding activity of these constitutive transcription factors during Dex-induced apoptosis in thymocytes to assess their functionality. We observed a progressive loss of the DNA-binding proteins in parallel with the appearance of the characteristic morphological and biochemical features of apoptosis. At the same time we have found a general increase in the nuclear proteolytic activity concomitant with a significant loss of the nuclear nonhistone chromosomal proteins. Indeed, cotreatment of thymocytes with the nonspecific serine protease inhibitor phenylmethylsulphonyl fluoride was able to partially protect the stability of the DNA-binding proteins and alter the expression of the c-fos and c-jun genes but did not inhibit apoptosis. Our results suggest that the action of a protease(s) is responsible for the degradation of constitutive transcription factors during Dex-induced apoptosis, rendering the death pathway irreversible.
Insights
Dexamethasone-induced apoptosis in thymocytes involves protease-mediated degradation of DNA-binding proteins. This degradation of transcription factors contributes to irreversible cell death, even when protease activity is inhibited.
Area of Science:
- Molecular Biology
- Cell Biology
- Immunology
Background:
- Dexamethasone (Dex) accelerates thymocyte apoptosis, a process linked to gene expression.
- Immediate early genes like c-fos and c-jun are implicated in regulating this apoptosis.
- Constitutive transcription factors modulate the expression of these immediate early genes.
Purpose of the Study:
- To analyze the DNA-binding activity of constitutive transcription factors during Dex-induced thymocyte apoptosis.
- To investigate the role of nuclear proteolysis in the degradation of these factors.
- To assess the impact of protease inhibition on apoptosis and gene expression.
Main Methods:
- Analysis of DNA-binding activity of constitutive transcription factors in thymocytes undergoing Dex-induced apoptosis.
- Measurement of nuclear proteolytic activity and nonhistone chromosomal protein levels.
- Assessment of apoptosis markers and c-fos/c-jun gene expression in thymocytes treated with Dexamethasone and phenylmethylsulphonyl fluoride.
Main Results:
- Progressive loss of DNA-binding proteins correlated with apoptosis.
- Increased nuclear proteolytic activity and decreased nonhistone chromosomal proteins observed.
- Phenylmethylsulphonyl fluoride partially protected DNA-binding proteins and altered c-fos/c-jun expression but did not inhibit apoptosis.
Conclusions:
- Protease action is responsible for the degradation of constitutive transcription factors during Dex-induced apoptosis.
- This degradation of transcription factors contributes to the irreversibility of the apoptotic pathway.
- Inhibition of proteases does not prevent apoptosis but affects gene expression and protein stability.