Phosphorylation of IκBα at Serine 32 by T-lymphokine-activated Killer Cell-originated Protein Kinase Is Essential for Chemoresistance against Doxorubicin in Cervical Cancer Cells

T-lymphokine-activated killer cell-originated protein kinase (TOPK) is known to be up-regulated in cancer cells and appears to contribute to cancer cell proliferation and survival. However, the molecular mechanism by which TOPK regulates cancer cell survival still remains elusive. Here we show that TOPK directly interacted with and phosphorylated I kappa B alpha at Ser-32, leading to p65 nuclear translocation and NF-kappa B activation. We also revealed that doxorubicin promoted the interaction between nonphosphorylated or phosphorylated TOPK and I kappa B alpha and that TOPK-mediated I kappa B alpha phosphorylation was enhanced in response to doxorubicin. Also, exogenously overexpressed TOPK augmented transcriptional activity driven by either NF-kappa B or inhibitor of apoptosis protein 2 (cIAP2) promoters. On the other hand, NF-kappa B activity including I kappa B alpha phosphorylation and p65 nuclear translocation, as well as cIAP2 gene expression, was markedly diminished in TOPK knockdown HeLa cervical cancer cells. Moreover, doxorubicin-mediated apoptosis was noticeably increased in TOPK knockdown HeLa cells, compared with control cells, which resulted from caspase-dependent signaling pathways. These results demonstrate that TOPK is a molecular target of doxorubicin and mediates doxorubicin chemoresistance of HeLa cells, suggesting a novel mechanism for TOPK barrier of doxorubicin-mediated cervical cancer cell apoptosis.