The catalytic subunit of DNA-PK has a unique function in inflammation independently of Ku70 and DNA repair: a new opportunity to target the enzyme without interfering with DNA repair

Abstract

Abstract Our laboratory demonstrated a critical role for DNA-dependent protein kinase (DNA-PK) in asthma pathogenesis via modulating the pertinent immune responses. DNA-PK is DNA repair enzyme composed of a catalytic subunit (DNA-PKcs) and two DNA-binding subunits (Ku70 and Ku80). Human cells express high levels of DNA-PK, surprisingly such high levels do not confer increased ability to repair DNA damage. Here we show that the role of DNA-PK in promoting inflammatory responses is independent of its function in the DNA repair. We examined the effect(s) of partial depletion of Ku70 on Ovalbumin (OVA) induced lung inflammation in mouse model of the disease. Of note, depletion of Ku70 by gene heterozygosity causes deficiency in DNA-PK-dependent DNA repair. Unlike the protective effects provided by DNA-PKcs gene heterozygosity, Ku70 heterozygosity did not alter the OVA-induced eosinophilia, mucus hypersecretion, Th2 cytokines production, or OVA-specific IgE upon OVA challenge. Interestingly, Ku70 heterozygosity enhanced methacholine-induced AHR over that of WT mice. Using a cell culture system, we demonstrate that while IL-4 and TNF-α are potent inducers of DNA-PKcs, such activation did not coincide with any detectable DNA damage or repair responses. Remarkably, while Ku70−/− blocked DNA-PKcs autophosphorylation in response to the DNA damage agent, etoposide, it did not affect the kinase in response to TNFα. Our findings suggest that the mechanism by which DNA-PK functions in inflammation is completely unrelated to its role in DNA repair, thus, unraveling a completely novel function for the kinase. More importantly, this provides a window of opportunity to target DNA-PK in inflammatory diseases without interfering with DNA repair processes.