Abstract LB-68: MYCN-induced TRPM7 expression and channel activity occurs through a mechanism that involves ornithine decarboxylase

Abstract

Abstract Neuroblastoma (NB) is an extra-cranial solid cancer in children. MYCN is a transcription factor that regulates the expression of genes that are involved in cell proliferation, growth, cell migration, etc. MYCN gene amplification is a prognostic indicator of poor outcome in NB. Recent studies have shown that intracellular free calcium regulates multiple steps involved in cell migration. Although significant advances have been made in understanding the role of calcium during migration, little has been achieved towards understanding its impact on the malignant progression of NB. Our results showed that MYCN gene amplification or over-expression of MYCN in NB cells increased TRPM7 expression, increased peak TRPM7 current, induced constitutive TRPM7 channel activity, enhanced calcium signaling, and promoted cell migration, implicating TRPM7 as a potential regulator of calcium signals that promote NB cell migration and invasion. Recent results suggest that MYCN may regulate TRPM7 expression through a process that involves ornithine decarboxylase (ODC), a rate limiting enzyme in the biosynthesis of polyamines, and a direct transcriptional target of MYCN. Treatment of NB cells with α-difluoromethylornithine (DFMO), an irreversible inhibitor of ODC, or transfection of ODC specific siRNA effectively decreased TRPM7 expression. This effect was attenuated by supplementing the culture media with spermidine, confirming that ODC may function downstream of MYCN to regulate TRPM7 expression. Interestingly, western blot analysis of NB cell lysates showed that MYCN induced the cleavage of the TRPM7 kinase domain, a post-translational modification that has been shown to increase TRPM7 currents and induce constitutive TRPM7 channel activity. Additionally, DFMO inhibited TRPM7 cleavage, an effect that was reversed by spermidine supplementation. Taken together, these results suggest that MYCN may regulate TRPM7 expression and channel activity through a mechanism that involves ODC-mediated polyamine biosynthesis. Citation Format: Dana-Lynn T. Koomoa, Ingo Lange. MYCN-induced TRPM7 expression and channel activity occurs through a mechanism that involves ornithine decarboxylase. [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 LB-68. doi:10.1158/1538-7445.AM2014-LB-68