Investigating the effects of Wnt/β-catenin Signalling on Melanoma Cell Metabolism and Mitochondrial Dynamics

Wnts are secreted morphogens that play pivotal roles in embryonic development, stem cell biology and a number of disease states including cancer. Most Wnts signal through a pathway that results in the stabilisation of an intracellular signalling molecule called β-catenin. In melanoma cells, Wnt/β-catenin signalling has been implicated as a key regulator of cellular invasion and metastasis. Using both transient and stable enhancement of Wnt/β-catenin signalling, I have found that mutation–based dysregulation of PI3K signalling dictates the invasive capacity of melanoma cell lines in response to Wnt3a stimulation. I demonstrate by confocal imaging that WNT3A facilitates perinuclear localisation of mitochondria with higher levels of mitochondrial networking and they show significant changes in the proteins of mitochondrial dynamics. Observed changes in mitochondrial fusion and fission proteins including MFN1, MFN2, OPA1 and DNM1L suggest that activation of Wnt/β-catenin signalling can increase mitochondrial fusion and decrease mitochondrial fission in melanoma cells. Cellular metabolic analysis using the Seahorse Bioscience XFe96 Analyzer suggests that Wnt/β-catenin mediated mitochondrial fusion may cause a global down-regulation of cellular energy metabolism in melanoma cells. This is supported by biochemical analysis of citrate synthase and lactate dehydrogenase activity. Knockout of -catenin removes the mitochondrial fusion effect in these cells and reverses any Wnt driven reduction in migration and metabolism suggesting that -catenin is able to control mitochondrial function and dynamics. We show that -catenin binds to the mitochondrial regulatory protein PARK2 in melanoma cells and subsequently blocks the autophagy dependency of melanoma cells. In summary, we demonstrate that activation of Wnt/β-catenin signalling in melanoma cells can lead to reduced cellular metabolism coupled with highly altered mitochondrial dynamics. This novel finding, controlled by -catenin, has potentially wide implications for understanding how certain context-dependent effects of Wnt/β-catenin signalling may be secondary to the regulation of mitochondrial dynamics and global cellular metabolism