Abstract C130: Inhibition of NF-κB activity promotes radiosensitivity of breast cancer cells in three-dimensional culture via a β1-integrin-mediated pathway.

Abstract

Abstract Radioresistance markedly impairs the efficacy of tumor radiotherapy and involves prosurvival signal transduction pathways that prevent radiation-induced cell death. Nuclear factor-κB (NF-κB), a stress-sensitive heterodimeric transcription factor in the regulation of the stress-responsive genes, has been shown to initiate prosurvival signaling in response to ionizing radiation (IR). The cooperative function of NF-κB with other key stress elements in radioresistance has not been clearly defined. We have previously reported that induction of β1-integrin is associated with the enhanced cell survival of breast cancer cells after exposure to clinically relevant doses of IR. Because a typical NF-κB binding site was identified in human β1-integrin promoter region, β1-integrin-mediated resistance to radiation may be regulated by NF-κB. The aim of the present study was to reveal a connection between NF-κB and β1-integrin pathways in radioprotection of malignant T4-2 mammary epithelial cells in 3D lrECM (three-dimensional laminin-rich extracellular matrix). We show that the elevated NF-κB activity was correlated with enhanced clonogenic survival with an increase in total and phosphorylated (Thr 788/789) β1-integrins. Inhibition of NF-κB activation significantly reduced clonogenic survival with the inhibition of β1-integrin, suggesting that NF-κB-mediated induction of β1-integrin is associated with an increased radiation resistance. Treatment of malignant human breast cell colonies, T4-2 with NF-κB activation inhibitor at Day 4 in 3D lrECM before exposure to IR (4-Gy X-ray) resulted in a reduction of the size of colonies. The surviving colonies were associated with a decrease in proliferation and increase in apoptosis, indicating a decrease of resistance to IR. Using an ELISA-based DNA binding assay, we next determined that the binding of NF-κB to its target sequence on β1-integrin promoter region was significantly increased by IR. These data suggest that IR-induced increase in β1-integrin protein expression is mediated by NF-κB activation and subsequent binding of NF-κB to the β1-integrin promoter. Taken together, our results provide the first evidence that NF-κB-mediated β1-integrin expression is responsible for tumor radioresistance. The NF-κB/β1-integrin pathway could provide new insight into the development of new therapeutic modalities to re-sensitize radioresistant tumor cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C130.