Department of Pharmacology and Chemical Biology

Synergism of the molecular axes PARP1-KLF4 and USP11-BRCA1 in breast cancer treatment


Our recent identification of interaction between KLF4 and PARP1 based on mass spectrometry leads to the characterization of PARP1-mediated KLF4 ADP-ribosylation in the recruitment of KLF4 to chromatin that is a critical step in ensuring KLF4-governed transcriptional function. Given the vital role of KLF4 in determining the cell-fate in response to DNA damage through regulating p21 and Bax, demonstration of KLF4 PARylation by PARP1 has revealed a new paradigm as to how cancer cells are sensitized to radiation or chemotherapeutic agents. We are now elucidating the mechanism by which KLF4 is modified by PARylation and how ADP-ribosylation of KLF4 leads to recruitment of KLF4 onto chromatin. In addition, we recently observe that inhibition of BRCA1 deubiquitination, a mechanism that stabilizes BRCA1, results in enhanced efficacy for PARP inhibitor in killing breast cancer cells. We thus propose a synthetic lethality based strategy to treat breast cancer cells with either positive or negative BRCA1 background using combination of PARP1 and USP11 inhibitors in patient-driven breast cancer xenograft mouse model. This project is funded by NIH/NCI R01 grant (CA202963)

Proteolytic regulation of Rad17 in orchestrating checkpoint function and tumorigenesis

Genotoxic stress, such as environmental radiation and chemical mutagens, results in genomic instability leading to cancer. Both DNA-damage response and DNA repair are tightly regulated by posttranslational modifications. The pivotal role of posttranslational modification has been demonstrated in the recognition of DNA damage lesion sites, activation of DNA damage checkpoint response, recruitment of DNA repair elements and termination of DNA damage checkpoint following metabolic recovery from genotoxic stress. To systematically search for proteins that are ubiquitylated and degraded in response to genotoxic stress and to further examine their impact on genomic integrity and carcinogenesis, we have performed a high-throughput screening. One interesting candidate that we identified was Rad17, a checkpoint protein.  We  are   currently   investigating the mechanism   by which Rad17 is   ubiquitylated and   degraded in response to DNA damage signal. By purifying protein complex followed by mass spectrometry, we recently identified functional interaction between Rad17 and Cdh1/APC (E3 ligase) as well as between Rad17 and USP20 (deubiquitinase). We are now determining how failure in proteolytic regulation of Rad17 by Cdh1/APC and USP20 would affect genomic integrity and tumorigenesis by various tumor mouse models. In collaboration with clinical group, we are developing a new combinatorial therapy for melanoma/skin  cancer in synergistically targeting BRAF and ATR-Cdh1/APC-Rad17-Chk1 checkpoint pathway, using various combinations of BRAF inhibitor, ATR inhibitor, Chk1 inhibitor as well as Cdh1/Cdc20 inhibitor in an animal model.

rad 17
dna damage signaling