Abstract B090: Tyrosine 211 phosphorylation of PCNA: A new paradigm of linking cell proliferation to cancer stemness and metastasis
Authors: Wang Yuan-Liang , Lee Chuan-Chun , Lin Pei-Le , Shen Yi-Chun , Wu Wan-Rong , Xia Wei-Ya , Hung Mien-Chie , Wang Shao-Chun 
Published: March 2020

Abstract
Cancer metastasis is the fundamental cause of cancer-related death. While 5-year survival rate of breast cancer with local involvement is very optimistic, the number precipitately dropped for patients whose disease has spread to distant organs. Some cancer cells can remain dormant for a long time and evolve to full blown malignancy at a later time. Despite intensive study, the mechanisms underpinning metastasis and tumor dormancy continue to drive cancer morbidity. PCNA forms a homotrimer ring encircling the DNA double helix and acts as a sliding platform indispensable for DNA replication, DNA damage repair, and chromatin remodeling. While a positive role of PCNA in is conceivable, how PCNA functions in tumor progression remains elusive due to the embryonic lethal phenotype in PCNA-deficient mice. We have shown that PCNA is regulated by phosphorylation at tyrosine 211 (Y211) meditated through multiple growth factor-stimulated signaling pathways. Y211 phosphorylation enhances chromatin-bound PCNA to promote cell proliferation and is frequently detected in multiple human cancers including breast cancer. To further dissect its biological functions, we have generated genetic mouse strain in which Y211 is replaced with phenylalanine which is structurally similar to tyrosine but cannot be phosphorylated. Comparing to wild-type mice, 211F mice have significantly reduced mammary tumor formation upon induction by the carcinogen DMBA. To understand its biological role in oncogene-induced mammary tumorigenesis, mice were crossed with the MMTV-PyMT mice in which mammary gland expression of the oncogene polyoma virus middle T antigen (PyMT) is driven by the mouse mammary tumor virus (MMTV) enhancer/promoter. Female 211F/PyMT mice have statistically significant but only moderate decrease in mammary tumor development. However, their lung metastasis is dramatically ablated compared to WT/PyMT mice harboring primary tumors of similar size. These results suggest that pY211-PCNA has an essential function not only in tumorigenesis but more importantly in progression to distant metastasis. Consistently, mammary tumors derived from WT/PyMT mice exhibits more pronounced stromal activity than tumors of 211F/PyMT mice. The suppression of metastasis and stromal activity in 211F/PyMT mice is associated with reduced number of tumor-initiating cells (TICs) as determined by in vitro and in vivo analyses. Further study using syngeneic orthotopic model of transplanting murine cancer cells into the mammary glands of WT and 211F mice unveils an unexpected function of pY211-PCNA in the stromal compartment on tumor development. Thus, our study reveals a novel tumor-promoting function of PCNA in both parenchymal and stromal compartments besides its traditional role in cell proliferation. Numerous FDA-approved drugs are targeting the signaling pathways leading to Y211 phosphorylation, suggesting that pY211-PCNA is a new druggable mechanism to target tumor metastasis.
Citation Format: Yuan-Liang Wang, Chuan-Chun Lee, Pei-Le Lin, Yi-Chun Shen, Wan-Rong Wu, Wei-Ya Xia, Mien-Chie Hung, Shao-Chun Wang. Tyrosine 211 phosphorylation of PCNA: A new paradigm of linking cell proliferation to cancer stemness and metastasis [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr B090. doi:10.1158/1535-7163.TARG-19-B090