Wnt signaling controls radiosensitivity via cyclooxygenase-2-mediated Ku expression in head and neck cancer

It has been proposed that Wnt signaling pathway may be a key radioprotective mechanism in irradiated cancer cells; however, the specific radioresistance mechanisms remain not to be fully clarified. Here we elucidate a novel signaling pathway of radioresistance in head and neck cancer (HNC) cell lines involving interactions among the Wnt signaling pathway, cyclooxygenase-2 (COX-2) and Ku expression. Activation of the Wnt signaling pathway by (2'Z,3'E)-6-bromoindirubin-3'-oxime (BIO) resulted in beta-catenin cytoplasmic accumulation and translocation to the nucleus, upregulated Ku expression and increased radioresistance in the COX-2-expressing HNC cell line. In contrast, Wnt singaling activation by BIO had no effects on Ku expression and radiosensitivity in a HNC cell line negative for COX-2. Interactions between Wnt singaling and Ku were indirectly regulated by COX-2. Blockage of COX-2 signaling led to the suppression of beta-catenin-induced Ku expression, and to consequent recovery of the radiosensitivity in HNC cells. Our results conclusively suggest that beta-catenin plays a pivotal role in the regulation of Ku expression via the proposed COX-2 intracellular pathway, thus supporting a novel radioresistance mechanism of HNC.