The Role of PAD4 in Chromatin Decondensation

Open Access
- Author:
- Leshner, Marc
- Area of Honors:
- Microbiology
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Yanming Wang, Thesis Supervisor
Yanming Wang, Thesis Supervisor
Dr. Teh-hui Kao, Thesis Honors Advisor
Dr. Wendy Hanna-Rose, Faculty Reader - Keywords:
- PAD4
- Abstract:
- ABSTRACT NETosis, the process where neutrophils release highly decondensed chromatin, better known as neutrophil extracellular traps (NETs), has gained much attention as an efficient means of killing bacteria. In vivo, NETs are induced by bacteria and proinflammatory cytokines. Our lab has shown that peptidyl arginine deiminase 4 (PAD4), an enzyme that converts Arg or monomethyl-Arg to citrulline in histones, is essential for NET formation. We found that areas of extensive chromatin decondensation, along NETs, are rich in histone citrullination. Although the mediators involved in NET formation are known, the overall mechanism underlying higher-order chromatin structure changes has yet to be elucidated. Upon investigating the effect of global citrullination in vivo, we have discovered that PAD4 overexpression in U2OS cells is sufficient to cause extensive chromatin decondensation independent of apoptosis. The highly decondensed chromatin is released to the extracellular space and stains strongly by a histone citrulline-specific antibody. The structure of the decondensed chromatin is reminiscent of NETs but is unique in that it occurs devoid of stimulation of cells with proinflammatory cytokines, bacteria or calcium ionophore treatment. By using this PAD4 overexpression model system in U2OS cells, we have begun to unveil the process of PAD4 mediated chromatin decondensation and show that intracellular concentrations of calcium, the activity of PAD4, and changes in higher-order chromatin regulators (i.e. NPM1) are essential for the decondensation process.