Identification of NF-kappaB and DNA-dependent protein kinase (DNA-PK) as new players in the regulation and signaling of the oncogenic phosphatase Wip1

Wild-type p53-induced phosphatase 1 (Wip1) is a stress-induced nuclear type 2C protein phosphatase (PP2C) that is over-expressed and amplified in many types of cancers. Further studies have shown Wip1 to act as an oncogene by inhibiting tumor suppressors such as p16/p19, p53, and ATM. The physiological role of Wip1 is to facilitate the return of the cell to homeostasis by inhibiting apoptosis and cell cycle arrest through the inactivation of several key stress signaling proteins such as p38, p53, and ATM. However, this physiological function may possibly be an additional oncogenic property of Wip1, since this may lead to premature inhibition of stress signaling and genomic instability in cases when Wip1 is over-expressed. Due to its oncogenic properties, Wip1 is an attractive drug target for human cancers, and, therefore, understanding Wip1 molecular functions is important. The studies outlined in this project identify novel regulation of Wip1 as well as novel Wip1 targets after stress and in a cancer setting. Nuclear factor-kappa B (NF-kappaB) directly induced or inhibited Wip1 expression at the transcriptional level depending on the cellular context. Additionally, Wip1 enhanced NF-kappaB activation in certain contexts by reducing the expression of the NF-kappaB inhibitor, Inhibitor of NF-kappaB-alpha (IkappaBalpha). DNA-PK, a major enzymatic complex important for the Non-Homologous End-Joining DNA double strand break repair process, was identified as a Wip1 target. Specifically, Wip1 reduced phosphorylation levels of the catalytic subunit of DNA-PK (DNA-PKcs) at the activating residue Thr2609. As a consequence, Wip1 inhibited NHEJ after genotoxic stress. These results contribute to the understanding of the functions of Wip1 in both a physiological and tumorigenic setting. New roles for NF-kappaB and DNA-PK in Wip1 signaling were identified, which have direct implications in the understanding of Wip1 oncogenic functions and the treatment of human cancer.