Optical Redox Imaging Is Responsive to TGFβ Receptor Signalling in Triple-Negative Breast Cancer Cells

Co-enzyme nicotinamide adenine dinucleotide NAD(H) regulates hundreds of biochemical reactions within the cell. We previously reported that NAD(H) redox status may have prognostic value for predicting breast cancer metastasis. However, the mechanisms of NAD(H) involvement in metastasis remain elusive. Given the important roles of TGFβ signalling in metastatic processes, such as promoting the epithelial-to-mesenchymal transition, we aimed to investigate the involvement of the mitochondrial NAD(H) redox status in TGFβ receptor signalling. Here we present the initial evidence that NAD(H) redox status is responsive to TGFβ receptor signalling in triple-negative breast cancer cells in culture. The mitochondrial NAD(H) redox status was determined by the optical redox imaging (ORI) technique. Cultured HCC1806 (less aggressive) and MDA-MB-231 (more aggressive) cells were subjected to ORI after treatment with exogenous TGFβ1 or LY2109761, which stimulates or inhibits TGFβ receptor signalling, respectively. Cell migration was determined with the transwell migration assay. Global averaging quantification of the ORI images showed that 1) TGFβ1 stimulation resulted in differential responses between HCC1806 and MDA-MB-231 lines, with HCC1806 cells having a significant change in the mitochondrial redox status, corresponding to a larger increase in cell migration; 2) HCC1806 cells acutely treated with LY2109761 yielded immediate increases in ORI signals. These preliminary data are the first evidence that suggests the existence of a cell line-dependent shift of the mitochondrial NAD(H) redox status in the TGFβ receptor signalling induced migratory process of breast cancer cells. Further research should be conducted to confirm these results as improved understanding of the underlying mechanisms of metastatic process may contribute to the identification of prognostic biomarkers and therapeutic targets.