Figure 1. DNA damage response and DNA repair are tightly regulated by ubiquitin pathway.
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 (Fig. 1). 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 (Fig. 2).
Figure 2. Identification of Rad17 as a DNA damage induced degradable protein by
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. This project is currently supported by NIH/NCI R01 grant (CA154695).