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Selective cleavage of nuclear autoantigens during CD95 (Fas/APO-1)-mediated T cell apoptosis
C A Casiano1, S J Martin, D R Green
1W. M. Keck Autoimmune Disease Center, Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, California 92037, USA.
Abstract:
Intracellular proteases appear to be important mediators of apoptosis. Substrates cleaved by proteases during apoptosis include nuclear autoantigens targeted in systemic autoimmune diseases. Using human autoantibodies as probes, we demonstrate here that T cell apoptosis mediated by CD95 (Fas/APO-1) is associated with substantial cleavage of a subset of nuclear autoantigens (7 of 33 examined). This subset included poly (ADP-ribose) polymerase, the 70-kD protein of the U1 small nuclear ribonucleoprotein particle, lamin B, the nuclear mitotic apparatus protein NuMA, DNA topoisomerases I and II, and the RNA polymerase I upstream binding factor UBF. Several of the cleaved autoantigens are involved in ensuring the integrity and proper conformation of DNA in the nucleus through interactions with the nuclear matrix, suggesting the possibility that their cleavage may contribute to the collapse of nuclear structure during apoptosis. The relative cleavage kinetics indicated that the autoantigens were targeted at various times after induction of apoptosis, suggesting either differential accessibility or activation of distinct proteases during the cell death process. These data reinforce the hypothesis that apoptosis is accompanied by selective cleavage of key substrates and not by a generalized degradation of intracellular material.
Insights
Cell death involves specific protein breakdown, not general degradation. Researchers found that T cell apoptosis cleaves key nuclear autoantigens, crucial for DNA integrity.
Area of Science:
- Cell Biology
- Molecular Biology
- Immunology
Background:
- Intracellular proteases play a role in programmed cell death (apoptosis).
- Nuclear autoantigens are targets in systemic autoimmune diseases and can be cleaved during apoptosis.
Purpose of the Study:
- To investigate the cleavage of nuclear autoantigens during T cell apoptosis mediated by CD95 (Fas/APO-1).
- To identify specific nuclear autoantigens cleaved during this process and understand their potential role in apoptosis.
Main Methods:
- Utilized human autoantibodies as probes to detect cleaved nuclear autoantigens.
- Examined the cleavage of 33 different nuclear autoantigens during CD95-mediated T cell apoptosis.
Main Results:
- Demonstrated substantial cleavage of 7 out of 33 examined nuclear autoantigens during T cell apoptosis.
- Identified cleaved autoantigens including poly (ADP-ribose) polymerase, U1 snRNP 70 kDa protein, lamin B, NuMA, DNA topoisomerases I and II, and UBF.
- Observed differential cleavage kinetics, suggesting sequential protease activation or varying substrate accessibility.
Conclusions:
- Apoptosis involves selective cleavage of key substrates, not generalized cellular degradation.
- Cleavage of autoantigens involved in DNA integrity may contribute to nuclear structure collapse during apoptosis.
- The findings support the hypothesis of targeted substrate proteolysis during programmed cell death.