Peptidylarginine deiminase inhibitors regulate autophagy of human cancer cells and inflammation response of immune cells
Open Access
- Author:
- Wang, Shu
- Graduate Program:
- Biochemistry, Microbiology, and Molecular Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- January 23, 2014
- Committee Members:
- Yanming Wang, Dissertation Advisor/Co-Advisor
Yanming Wang, Committee Chair/Co-Chair
Andrea Marie Mastro, Committee Member
David Scott Gilmour, Committee Member
Gong Chen, Committee Member
Robert Paulson, Committee Member - Keywords:
- PAD inhibitor; cancer epigenetics; ChIP-exo; citrullination; ER
- Abstract:
- In cancer cells, tumor suppressor genes are frequently silenced by enzymes that catalyze epigenetic histone modifications. Peptidylarginine deiminase 4 (PAD4), an enzyme that converts Arg or monomethyl-Arg to citrulline in histones, is markedly overexpressed in many human cancers. Previously, researchers in in our lab have found that PAD4 counteracts the function of protein arginine methyltransferase; and thus, alters the transcription status of p53 target genes, suggesting that PAD4 is a potential target for cancer treatment. Furthermore, PAD4 is expressed in neutrophils, and is essential for NET formation induced by bacteria and pro-inflammatory cytokines. In this dissertation, I will report the inhibition of the growth of cancer cells by the novel PAD inhibitors my colleagues and I generated. Among those with low micromolar IC50, YW3-56 induced p53 target gene SESN2 (sestrin 2, a negative regulator of mTOR signaling); and thus, inhibited the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway in p53 wild type osteosarcoma U2OS cancer cells. In U2OS cells, PAD4 functions as a co-repressor of p53 to regulate SESN2 expression. However, YW3-56 inhibits the growth of diverse cancer cells in a p53 independent manner. In the p53 mutant breast cancer MDA-MB-231 cells, YW3-56 triggers a type of cell death distinct from apoptosis, one that shows mitochondria depletion, mTORC1 inhibition, and blocking of autophagy. I investigated the mechanism underlying the growth inhibition effect of YW3-56 in the MDA-MB-231 cells and identified ATF4, a transcription factor in the ER stress pathway, as the novel transcription regulator mediating SESN2 expression. Using YW3-56 as a query tool, I found that ATF4 WAS required for YW3-56-induced SESN2 expression. Forced expression of ATF4 was sufficient to activate SESN2. With the detection of the ATF4 binding site on SESN2 promoter region, we identified the ATF4-SESN2 transcription circuit as a novel link between the ER stress and the mTORC1 signaling pathway. Furthermore, YW3-56 treatment triggered ROS accumulation in MDA-MB-231 cells, and the YW3-56 induced ATF4 target gene expression was ROS dependent. This finding suggests that ROS might active other factors that cooperate with ATF4 for transcription regulation. In nude mice xenograft experiments, we found that YW3-56 was effective in inhibiting the growth of tumors derived from the MDA-MB-231 subline 1833TR cells. Its antitumor efficiency also correlated with the gene transcription profiling featured a significant induction of SESN2. Taken together, ATF4-SESN2 circuit could be a potential therapeutic target for p53 mutant cancers. In this thesis, I unveiled the anticancer mechanisms and therapeutic potential of the pan-PAD inhibitor YW3-56.