PAD4 MEDIATED CANCER EXTRACELLULAR CHROMATIN NETWORK IN BREAST CANCER PROMOTES THE DEVELOPMENT AND PROGRESSION OF LUNG METASTASIS

Open Access
- Author:
- Shi, Lai
- Graduate Program:
- Molecular, Cellular and Integrative Biosciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 26, 2019
- Committee Members:
- Yanming Wang, Dissertation Advisor/Co-Advisor
Yong Wang, Committee Chair/Co-Chair
Siyang Zheng, Committee Member
Yanming Wang, Committee Member
Robert Paulson, Outside Member - Keywords:
- PAD4
Hypercitrullination
Cancer Extracellular Chromatin Network
Breast cancer
Lung metastasis - Abstract:
- Peptidyl Arginine Deiminase 4 (PAD4/PADI4) is a posttranslational modification enzyme to convert protein arginine or mono-methylarginine to citrulline. The PAD4 mediated hypercitrullination reaction in neutrophils leads to the decondensation of chromatin and the release of nuclear chromatin to form a chromatin network termed Neutrophil Extracellular Traps (NETs). NETs are first described as antimicrobial fibers that bind and kill bacteria and deemed as a self-defensive mechanism used by neutrophils. Interestingly, excessive level of NETs is later demonstrated to cause many autoimmunity diseases and cancer. They can facilitate cancer metastasis and awaken dormant cancer cells. Thus, NETs are actually a double-edged sword both beneficial and detrimental to human health depending on the level and context. PAD4 can also lead to extracellular chromatin trap in other cell types like macrophages and eosinophils and is found to be highly expressed in human tumor tissues by pathologists. However, previous researches only focus on its role in gene regulation in cancer cells and it is unknown if PAD4 can mediate the release of chromatin DNA to the extracellular space in cancer cells. Here, we report that murine breast cancer 4T1 cells with high levels of Padi4 expression can release Cancer Extracellular Chromatin Network (CECN) in vitro and in vivo. Depletion of tumor Padi4 using CRISPR/Cas9 abolished CECN formation in 4T1 cells. Padi4 deletion in 4T1 cells reduced tumor growth rate in an allograft model, and more strikingly 4T1 cancer cells with Padi4 deletion showed drastically decreased breast to lung metastasis. Meanwhile, DNase I treatment also reduced breast to lung metastasis of Paid4 wild type 4T1 cells in allograft experiments in the Padi4 knockout mice. We further demonstrated that the block of CECN does not alter circulating tumor cells but decreases metastasis through steps after intravasation. Our work thus unveils PAD4 plays a cell autonomous role in cancer metastasis. Our work reveals a novel mechanism for targeted cancer treatment by blocking CECN formation to prevent cancer metastasis.