A Splice Variant of the Human Ion Channel TRPM2 Modulates Neuroblastoma Tumor Growth Through HIF-1/2{alpha} [Cell Biology]

November 12th, 2014 by Chen, S.-j., Hoffman, N. E., Shanmughapriya, S., Bao, L., Keefer, K., Conrad, K., Merali, S., Takahashi, Y., Abraham, T., Hirschler-Laszkiewicz, I., Wang, J., Zhang, X.-Q., Song, J., Barrero, C., Shi, Y., Kawasawa, Y. I., Bayerl, M., Sun, T., Barbour

The calcium permeable ion channel TRPM2 is highly expressed in a number of cancers. In neuroblastoma, full length TRPM2 (TRPM2-L) protected cells from moderate oxidative stress through increased levels of Forkhead transcription factor 3a (FOXO3a) and superoxide dismutase 2 (MnSOD). Cells expressing dominant negative short isoform (TRPM2-S) had reduced FOXO3a and MnSOD levels, reduced calcium influx in response to oxidative stress, and enhanced ROS, leading to decreased cell viability. Here, in xenografts generated with SH-SY5Y neuroblastoma cells stably expressing TRPM2 isoforms, growth of tumors expressing TRPM2-S was significantly reduced compared to tumors expressing TRPM2-L. Expression of HIF-1/2α was significantly reduced in TRPM2-S expressing tumor cells, as was expression of target proteins regulated by HIF-1/2α including those involved in glycolysis (LDHA, ENO2), oxidant stress (FOXO3a), angiogenesis (VEGF), mitophagy and mitochondrial function (BNIP3 and NDUFA4L2), and mitochondrial electron transport chain activity (complex IV, cytochrome oxidase 4.1/4.2). The reduction in HIF-1/2α was mediated both through significantly reduced HIF-1/2α mRNA levels and increased levels of von Hippel-Lindau in TRPM2-S expressing cells. Inhibition of TRPM2-L by pretreatment with clotrimazole or expression of TRPM2-S significantly increased sensitivity of cells to doxorubicin. Reduced survival of TRPM2-S expressing cells after doxorubicin was rescued by gain of HIF-1 or 2α function. These data suggest that TRPM2 activity is important for tumor growth, and cell viability and survival following doxorubicin, and that interference with TRPM2-L function may be a novel approach to reduce tumor growth through modulation of HIF-1/2α, mitochondrial function and mitophagy.