Pathology of hereditary renal cell carcinoma syndromes: Tuberous sclerosis complex (TSC)

Tuberous sclerosis complex (TSC) is an autosomal dominant genetic disease characterized by hamartomatous tumors involving multiple organs such as the brain, skin, heart, lung and kidney. TSC is caused by inactivating mutations in TSC1/TSC2, which encodes hamartin and tuberin, respectively, and forms a complex that regulates mechanistic target of rapamycin complex 1 (mTORC1), resulting in cell overgrowth and oncogenesis. Since a leading cause of morbidity and mortality in TSC relates to chronic kidney disease and the ability to preserve renal function, this review describes the important pathologic findings in TSC-associated renal neoplasms and their correlating sporadic counterparts. The most common renal tumor in TSC patients are AMLs, followed by a heterogeneous spectrum of renal epithelial tumors, which may provide clues to establishing a diagnosis of TSC.

Ornithine aminotransferase supports polyamine synthesis in pancreatic cancer

There is a need to develop effective therapies for pancreatic ductal adenocarcinoma (PDA), a highly lethal malignancy with increasing incidence1 and poor prognosis2. Although targeting tumour metabolism has been the focus of intense investigation for more than a decade, tumour metabolic plasticity and high risk of toxicity have limited this anticancer strategy3,4. Here we use genetic and pharmacological approaches in human and mouse in vitro and in vivo models to show that PDA has a distinct dependence on de novo ornithine synthesis from glutamine. We find that this process, which is mediated through ornithine aminotransferase (OAT), supports polyamine synthesis and is required for tumour growth. This directional OAT activity is usually largely restricted to infancy and contrasts with the reliance of most adult normal tissues and other cancer types on arginine-derived ornithine for polyamine synthesis5,6. This dependency associates with arginine depletion in the PDA tumour microenvironment and is driven by mutant KRAS. Activated KRAS induces the expression of OAT and polyamine synthesis enzymes, leading to alterations in the transcriptome and open chromatin landscape in PDA tumour cells. The distinct dependence of PDA, but not normal tissue, on OAT-mediated de novo ornithine synthesis provides an attractive therapeutic window for treating patients with pancreatic cancer with minimal toxicity.

O-GlcNAc Regulates CD4+ T Cell Differentiation

Chronic inflammation is a feature of obesity and enhances the risk of heart disease, cancer, and diabetes. Specifically, pro-inflammatory TH1 and TH17 CD4+ effector T cells are increased in metabolic diseases. However, a clear molecular mechanism linking metabolic changes with pro-inflammatory T cells is lacking. We hypothesize that elevated levels of O-linked β-N-acetylglucosamine (O-GlcNAc), a post-translational modification (PTM) of nuclear and cytoplasmic proteins, promotes pro-inflammatory CD4+ T cell differentiation. Since production of O-GlcNAc involves input from multiple metabolic pathways, the PTM acts as a nutrient sensor. To investigate the role of O-GlcNAc in a setting of metabolic disease, we analyzed O-GlcNAc levels in CD4+ T cells in mice fed a high fat diet. CD4+ T cells from obese mice have elevated O-GlcNAc levels and are primed to secrete more IL-17A, the eponymous TH17 cytokine, and IFNγ, the signature TH1 cytokine. We also cultured mouse splenic CD4+ T cells with Thiamet-G (TMG), a selective inhibitor of the enzyme that removes O-GlcNAc. We find a significant increase in protein and transcript levels of IL-17A and IFNγ in TMG treated cells. Acetyl CoA carboxylase (ACC1), the rate limiting enzyme in fatty acid synthesis, is known to enhance generation of TH17 cells by producing ligands that increase the activity of RORγt, the transcription factor defining the TH17 lineage. We find that ACC1 is O-GlcNAcylated in CD4+ T cells. Collectively, our data suggest that elevated O-GlcNAc levels prime TH17 CD4+ T cell differentiation by altering ACC1 activity. Further study into how O-GlcNAcylation promotes pro-inflammatory T cell differentiation will provide insight into how nutritional excess exacerbates inflammation.

O-GlcNAc regulates CD4+ T cell differentiation

Chronic inflammation is a feature of diabetes and obesity and enhances the risk of atherosclerosis and cancer. Specifically, proinflammatory Th1 and Th17 CD4+ T cells are increased in metabolic diseases. However, a clear molecular mechanism linking metabolic changes with proinflammatory T cells is lacking. We hypothesize that elevated levels of O-linked β-N-acetylglucosamine (O-GlcNAc), a post-translational modification of nuclear and cytoplasmic proteins, promotes proinflammatory CD4+ T cell differentiation. Since production of O-GlcNAc involves input from carbohydrate, amino acid, fatty acid, and nucleic acid metabolism, the modification acts as a general sensor of a cell’s nutritional status. To investigate O-GlcNAc’s role, we cultured mouse splenic CD4+ T cells with Thiamet-G (TMG), a selective inhibitor of the enzyme that removes O-GlcNAc (O-GlcNAcase, OGA), before activating with anti-CD3 and anti-CD28 under permissive Th0 conditions. We find a significant two-fold increase in protein and transcript levels of IL-17A, the eponymous Th17 cytokine. Intracellular cytokine staining shows two-fold increases in IFNγ+ cells, IL-17+ cells, and IFNγ+IL-17+ cells. Phosphorylation of STAT3 and STAT4, the transcriptionally active form of STATs which define the Th17 and Th1 lineage programs respectively, is increased in TMG-treated cells within 10 minutes of T cell receptor activation. Collectively, our data suggest that elevated O-GlcNAc levels prime Th17, Th1, and Th1-like Th17 CD4+ T cell differentiation by increasing activated STAT3 and STAT4. Further study into the molecular mechanism of how O-GlcNAcylation promotes proinflammatory T cells may provide insight into how nutritional excess exacerbates inflammation.