Function of polo-like kinase 3 in NF-κB-mediated proapoptotic response

Abstract

RelA, the p65 subunit of NF-κB transcription factors, plays a key role in regulation of antiapoptotic and pro-apoptotic responses. However, the downstream target genes regulated by RelA-NF-κB in the initiation of pro-apoptotic signaling were not identified. We previously showed that RelA-NF-κB functioned as a proapoptotic factor by activating the p53-signaling pathway in response to doxycycline-induced superoxide. In the present study, we demonstrate that the ability of doxycycline/superoxide to induce expression of polo-like kinase 3 (Plk3) depends on NF-κB activity. We identified a κB binding site in the promoter of Plk3, and this κB site is directly involved in its induction by the RelA-NF-κB complex. Plk3 formed a complex with p53 and was involved in the phosphorylation of p53 on Ser-20 in response to superoxide. Inhibition of Plk3 expression by Plk3 small interfering RNA suppressed the doxycycline/ superoxide-mediated apoptosis. Overexpression of wild-type Plk3 in HCT116 p53+/+ cells induced rapid apoptosis, whereas overexpression of wild-type Plk3 in HCT116 p53-/- cells and the kinase-defective mutant Plk3K91R in p53+/+ cells induced delayed onset of apoptosis. Furthermore, mutagenesis of Plk3 showed that the N-terminal domain (amino acids 1-26) is essential for the induction of delay onset off apoptosis. These data show that Plk3 is a RelA-NF-κB-regulated gene that induces apoptosis in both p53-dependent and -independent signaling pathways, suggesting a possible mechanism for RelA-NF-κB-regulated proapoptotic responses. © 2005 by The American Society for Biochemistry and Molecular Biology, Inc.