Functions of the LKB1 tumor suppressor in control in metabolism and epigenetics

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Intermediates generated in cell metabolism also serve as substrates for covalent modification of chromatin, enabling the potential coupling of metabolic states and epigenetic control. This interplay between metabolic control and epigenetic reprogramming has been recently been proposed as a potential mechanism for regulation of stem cell differentiation and for pathologic processes such as cancer. We identify such a network as a major mediator of cell transformation downstream of the LKB1, an important tumour suppressor that is mutationally inactivated in many cancers (e.g. lung, pancreas). LKB1 encodes a serine-threonine kinase that integrates nutrient availability, metabolism and growth, although the mechanisms for LKB1-dependent tumour suppression remain elusive. By developing primary epithelial cell models and employing transcriptional, proteomics, and metabolic analyses, we find that oncogenic cooperation between LKB1 loss and KRAS activation, alterations commonly coinciding in human cancer, is fueled by pronounced rewiring of nutrient utilization. In particular, we demonstrate that LKB1 inactivation potentiates glycolysis while also channeling glycolytic intermediates to the serine-glycine-one carbon network coupled to generation of the methyl donor S-adenosylmethionine (SAM). In concert, DNA methyltransferases (DNMT1 and DNMT3A) are upregulated, leading to global elevation in genomic 5- methylcytosine levels. Correspondingly, LKB1 deficiency renders cells independent of exogenous serine for growth, but highly sensitive to inhibition of serine biosynthesis and DNA methylation in vitro and in vivo. Thus, we define a hypermetabolic state resulting from loss of LKB1 that links rewiring of glucose metabolism and chromatin regulation. This state both potentiates and is critically required for the tumorigenic program of LKB1- mutant cells, suggesting novel points of therapeutic intervention in defined patient subsets. Here, we will build on these exciting findings, with the goals of defining how this enhanced DNA methylation contributes to the tumor phenotypes, deciphering the signaling and transcriptional pathways by which LKB1 loss activates to SGOC network, and further establishing the therapeutic potential of targeting this pathway in relevant in vivo preclinical models.