Reward-related memories are essential for adaptive behavior and evolutionary fitness, but are also a core component of maladaptive brain diseases such as addiction. Reward learning requires dopamine neurons located in the ventral tegmental area (VTA), which encode relationships between predictive cues and future rewards. Recent evidence suggests that epigenetic mechanisms, including DNA methylation, are essential regulators of neuronal plasticity and experience-driven behavioral change. However, the role of epigenetic mechanisms in reward learning is poorly understood. Here, we reveal that the formation of reward-related associative memories in rats upregulates key plasticity genes in the VTA, which are correlated with memory strength and associated with gene-specific changes in DNA methylation. Moreover, DNA methylation in the VTA is required for the formation of stimulus-reward associations. These results provide the first evidence that that activity-dependent methylation and demethylation of DNA is an essential substrate for the behavioral and neuronal plasticity driven by reward-related experiences.

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Cite this articleGoldsmith ZK, McEwen MW, Kibe MW, et al. Sirtuin inhibitor as a novel cell cycle checkpoint and regulator of the TP53-MDM2 pathway in uveal melanoma. ABSTRACT PurposeThe liver is the most common site of uveal melanoma (UM) metastasis with approximately 50% of UM patients being affected. With no proven therapies that mitigate metastases the mortality rate is 85% within the first year after detection of the liver disease. In this study, we provide a mechanistic understanding of the de-regulation of the TP53-MDM2 pathway in UM, which plays a central role in tumor biology. MethodsWe investigated the TP53-MDM2 signaling pathway in the microenvironment of liver metastases taken from both a murine orthotopic xenograft and post-mortem metastatic UM human liver. These findings were studied in-depth using both primary and metastatic UM cell lines treated with the MDM2 antagonist Nutlin-3a and the sirtuin inhibitor and transcriptional activator of TP53, Tenovin-6. ResultsDe-regulation of the TP53-MDM2 signaling pathway is specific to the liver microenvironment, providing a survival mechanism for UM metastases. Tenovin-6, not Nutlin-3a, reduced UM cell survival by increasing the percentage of cell death and reducing the percentage of proliferating cells. Tenovin-6 increased acetylation of p53, reduced ubiquitination of the protein, and acted as a cell cycle regulator. ConclusionOur findings suggest that in patients with metastatic UM de-regulation of TP53-MDM2 signaling pathway promotes growth of the liver metastases and provides pre-clinical information on the potential of targeting of the TP53-MDM2 signaling pathway via Tenovin-6.