Abstract 3536: The biphasic mechanism of TNF-alpha mediated modulation of mdr1 expression and chemosensitization of colon cancer cells is linked to the NFkappaB pathway

Abstract

Abstract Multidrug resistance (MDR) is one major cause for cancer chemotherapy failure. Therefore, numerous overcoming strategies have been tested for tumor chemosensitization. Among these, persistent action of proinflammatory cytokines, such as tumor necrosis factor-alpha (TNF) showed great potential for downregulation of MDR-associated genes, particularly for the ABC-transporter P-glycoprotein Pgp, encoded by the mdr1 gene. These cytokine-mediated effects are still under controversial discussion, since transient action of TNF was shown to increase mdr1 expression, whereas persistent TNF action reduces mdr1 expression. Key mediator for this is the transcription factor NFkappaB/p65. This factor is acting via binding to NFkappaB/p65 consensus sequences within the mdr1 promoter. To determine the cellular mechanisms of TNF mediated modulation of mdr1 expression, we analyzed transient and persistent effects in regard to biphasic NFkappaB signaling in colon carcinoma cells. The mdr1 overexpressing, multidrug resistant human HCT15 colon carcinoma cells were treated for transient 30 to 120 min or long-term, 24 to 96 h incubations with TNF. The TNF mediated modulation of mdr1 expression was analyzed by real-time RT-PCR and Western-blot. Involvement of TNF-receptor I or II and time-dependent analysis of NFkappaB/p65 signaling was determined by Western blot, luciferase cell signaling reporter assay and EMSA. Our studies revealed that the persistent long-term action of TNF leads to down-regulation of mdr1 at mRNA and protein level. We showed, that this effect is mediated by TNF-receptor I, which is known to trigger the NFkappaB/p65 pathway. More importantly, the persistent TNF action on the colon cancer cells abolishes TNF mediated induction of the NFkappaB/p65 signaling, associated with reduced nuclear accumulation of NFkappaB/p65 and also its impaired binding to the consensus sequence of the mdr1 promoter. This study supports the biphasic nature of TNF action and points to the contrary effects of transient or persistent action of this cytokine. It provides insights into mechanism of MDR overcoming in colon cancer and potential clues for effects associated with chronic inflammation of the intestine Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3536.