Dr. Skoko’s research is focused on understanding how reactive oxygen and nitrogen species (ROS and RNS) control cell signaling pathways involved in breast cancer initiation, growth and metastasis as well as how these mechanisms can be exploited therapeutically. Of particular interest are H2O2 and electrophilic nitroalkenes, which can act as post translational modifications to regulate protein function by binding to redox reactive cysteine residues. Exploration of these species as redox signaling modulators of DNA repair pathways in breast cancer encompasses two primary lines of study.
 
1) The role of peroxiredoxin 1 (PRDX1) in DNA damage signaling.
Endogenously and exogenously generated ROS species can cause damage to intracellular proteins, lipids and DNA. A significant contributor to oxidant scavenging and the modulation of oxidatively-modified proteins is the PRDX family, which consists of six members that enzymatically reduce peroxides through an active site cysteine (peroxidatic cysteine, Cp). The PRDX proteins are subdivided into groups characterized by the presence of a “resolving” cysteine that enables a single (1-Cys; PRDX VI) or dual (2-Cys; PRDX I-IV and atypical 2-Cys; PRDX V) cysteine-dependent peroxide reduction. The Cp of PRDXs is highly reactive toward hydroperoxides, with rate constants ranging from 105 - 107 m−1 s−1. Through its peroxidase and signaling mediator activities, PRDX1 plays an important role in the prevention of malignancy. Prdx1+/- and Prdx1-/- mice display decreased lifespan due to the formation of lymphoma and various organ site sarcomas and carcinomas as well as hemolytic anemia. Isolated Prdx1-/- mouse embryonic fibroblasts (MEF) were further found to harbor increased 8-oxoguanine in DNA when compared to Prdx1+/+ MEFs. Also, levels of intracellular reactive species are elevated and display increased nuclear localization upon loss of PRDX1 activity. The role of PRDX1 in DNA damage signaling is being actively pursued.
 
2) Electrophilic nitroalkenes as homologous recombination inhibitors to sensitize triple-negative breast cancer to DNA damaging agents.
Fatty acid nitroalkenes are endogenously produced compounds formed via unsaturated fatty acid and nitric oxide or nitrite-dependent reactions. These molecules mediate several intracellular signaling pathways by adducting to reactive cysteine residues present in proteins including Keap1, NF-κB, PPARγ, and HSF-1. In our studies, a reactive thiol present in RAD51 was exploited to inhibit the homologous recombination DNA repair pathway in triple-negative breast cancer cells. Mechanistic studies revealed that electrophilic nitroalkenes can inhibit irradiation-induced RAD51 foci formation by post-translational adduction to RAD51 and inhibit tumor growth in vivo. Further studies continue to expand the effects of electrophilic nitroalkenes as anti-cancer agents by perturbation of DNA damage signaling in breast cancer in vivo.