Abstract 765: Short- and long-term TNF-alpha mediated NF-κB signaling exerts diverging effects on ABCB1/PgP expression

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Multidrug resistance (MDR) still represents one major obstacle for cancer chemotherapy. The ABC transporter ABCB1/PgP is an important factor mediating resistance of tumor cells towards cytostatic drug treatment. Among numerous overcoming strategies, persistent treatment of pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha) leads to down-regulation of MDR-associated genes, such as ABCB1. The transcription factor NF-κB/p65 is a known key regulator of ABCB1 expression. We analyzed short- and long-term effects of TNF-alpha regarding modulation of NF-κB/p65 signaling and ABCB1/PgP expression in colon carcinoma cells. Highly resistant ABCB1 endogenously overexpressing HCT15 human colon carcinoma cells were subjected to short- (30-120 min) or long-term (24-96 h) TNF-alpha treatment. TNF-alpha-mediated modulation of ABCB1/PgP expression was analyzed by real-time RT-PCR and Western-blot. The effect of TNF-receptor triggered NF-κB/p65 signaling on ABCB1/PgP expression was analyzed by Western blot, ABCB1 promoter reporter assays and by EMSA. The effects of TNF-alpha on drug accumulation and cytotoxicity were determined by FACScan analysis and MTT cytotoxicity assays. The studies revealed that long-term, but not short-term action of TNF-alpha leads to TNF-receptor 1-mediated down-regulation of ABCB1/PgP expression. It furthermore dampens NF-κB/p65 activation as well as IκBα resynthesis. This is associated with reduced nuclear accumulation of NF-κB/p65 and lack of its binding to the NF-κB/p65 consensus sequence in the ABCB1 promoter. In consequence long-term TNF-alpha treatment mediates significant increase in drug accumulation and sensitization of HCT15 cells towards drug treatment. The study reveals the diverging effects of short- or long-term TNF-alpha action and provides novel insights into mechanism of ABCB1 regulation by this pro-inflammatory cytokine. Citation Format: Wolfgang Walther, Lisa Bauer, Jutta Aumann, Dennis Kobelt, Ulrike S. Stein. Short- and long-term TNF-alpha mediated NF-κB signaling exerts diverging effects on ABCB1/PgP expression. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 765. doi:10.1158/1538-7445.AM2014-765