1. Obstacles in Renal Regenerative Medicine: Metabolic and Epigenetic Parallels Between Cellular Reprogramming and Kidney Cancer Oncogenesis 
Zsuzsanna Lichner, Fabrice Mac-Way, George M. Yousef 
European Urology Focus 
DOI: /j.euf
Copyright © Terms and Conditions

2. Fig. 1
Comparison of main molecular events in RCC pathogenesis and cellular reprogramming. The Warburg effect is a metabolic change that was indicated as a possible driver and an early event in RCC pathogenesis as well as in cellular reprogramming. Similarly, RCC and iPS cells share specific epigenetic changes and have overlapping miRNA expression patterns. ATP=adenosine triphosphate; RCC=clear cell renal cell carcinoma; iPSC=induced pluripotent stem cells; OXPHOS=oxidative phosphorylation; SWI/SNF=switch/sucrose nonfermentable; PBRM1=polybromo 1; ARID1A=AT-rich interaction domain 1A; SMARCA4=SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily A, member 4; SETD2=SET domain containing 2; BAP1=BRCA1-associated protein-1; BMI1=BMI1 proto-oncogene, polycomb ring finger; DNMT1=DNA (cytosine-5-)-methyltransferase 1.
European Urology Focus DOI: ( /j.euf )
Copyright © Terms and Conditions

3. Fig. 2
Interaction of metabolic pathways upon hypoxia. Under normoxic conditions, cells generate energy by aerobic cellular respiration. Theoretically, each glucose molecule generates six molecules of CO2, six molecules of water, and 38 ATP molecules, and glucose metabolism is dependent on the presence of oxygen. Complete catabolism of pyruvate (through TCA cycle and OXPHOS) would thus maximize ATP production but would restrict the production of high-energy precursors of the biomass, setting a limit to cell division. Under hypoxic conditions, the mitochondrial OXPHOS is truncated due to a lack of oxygen. Excess glucose is diverted to the pentose phosphate cycle to synthesize amino acids, nucleic acids, and fatty acids—all necessary components to build the actively dividing cells. Hypoxic cells are able to use glutamine as an alternative carbon source and metabolize it through reductive carboxylation, to further support amino acid and fatty acid synthesis. Inhibition of OXPHOS promotes reductive carboxylation. Interestingly, several oncogenes, such as RAS and MYC, cause mitochondrial dysfunction and thus promote metabolic rewiring of the cell. ATP=adenosine triphosphate; TCA=tricarboxylic acid; OXPHOS=oxidative phosphorylation.
European Urology Focus DOI: ( /j.euf )
Copyright © Terms and Conditions

4. Fig. 3
Aerobic glycolysis promotes pentose phosphate pathway (PPP). PPP generates NADPH and pentoses, such as ribose-5-phosphate and erythrose-4-phosphate. NADPH is used in reductive cellular metabolic steps, such as fatty acid synthesis, while ribose 5 phosphate is the precursor of nucleic acids and erythrose 4 phosphate is the precursor of aromatic amino acids. Glucose-6-phosphate, 3-phosphoglycerate, and pyruvate are common substrates for glycolysis and PPP. A recent study describes the uniform depletion of fructose-1,6-bisphosphatase 1 (FBP1) in RCC. FBP1 is a rate-limiting regulatory enzyme in gluconeogenesis. Its absence could streamline and expedite glycolysis, while it could also prevent FBP1 from binding and inhibiting the hypoxia-inducible factor 1 (HIF1). Unlike normal cells, cancer cells express the M2-PK splice variant of pyruvate kinase. M2-PK’s enzymatic activity is lower, leading to the accumulation of phosphoenolpyruvate (PEP). In M2-PK expressing cells, PEP acts as a phosphate donor and participates in the phosphorylation of phosphoglycerate mutase (PGAM1), while producing pyruvate through this alternative way of glycolysis. Additionally, M2-PK has nuclear functions as well, since it acts as a transcriptional coactivator of HIF1α and the POU Class 5 Homeobox 1 (OCT4). The sustained pyruvate production contributes to important anabolic reactions of the cell and supports rapid cell division. Lactate dehydrogenase (LDH) is overexpressed in cancer cells and is a potential biomarker for renal cell carcinoma progression. NADPH=nicotinamide adenine dinucleotide phosphate; M2-PK=a splice variant of pyruvate kinase; RCC=renal cell carcinoma.
European Urology Focus DOI: ( /j.euf )
Copyright © Terms and Conditions

5. Fig. 4
Metabolic consequences of the Warburg effect. The Warburg effect is a phenomenon that was originally described in cancer cells; it refers to an alternative energy producing mechanism that is based on the high rate of glycolysis and cytosolic lactate production. This phenomenon is likely a uniform property of highly proliferative cells. Cancer cells support the altered, aerobic glycolysis by additional metabolic adaptations, such as the ability to use glutamine as a major carbon source besides glucose, through reductive carboxylation. In parallel, oxidative phosphorylation (OXPHOS) is compromised, and reduced OXPHOS promotes reductive carboxylation (dotted arrow). Glutamine is deaminated to glutamate in the cytosol or in the mitochondria and is converted to α-ketoglutarate (α-KG) in an isocitrate dehydrogenase 1 and/or 2 (IDH1 and IDH2)–dependent manner; α-KG is either further carboxylated to isocitrate and citrate in the mitochondria, or follows the regular biochemical events of TCA cycle. Reductive metabolism of α-KG leads to the production of acetyl coenzyme A (Ac-CoA) and oxaloacetic acid (OAA). These metabolic building blocks (in black rectangles) are used for fatty acid and amino acid synthesis in the cytosol and will create the biomass of the tumor. Recent carbon tracing studies show that hypoxic cells and von Hippel–Lindau factor (VHL)–deficient renal cells preferentially use reductive carboxylation for lipid synthesis. Glutamate is also a predominant substrate for gluconeogenesis in kidney normal and hypoxic kidney cells. Glutamine is the most abundant amino acid in the human body and is the most important nitrogen source for the rapidly dividing cells. In the kidney, glutamate is the end product when glutaminase enzyme releases ammonia and urea. Hypoxic and/or VHL-deficient cells have increased glutamine consumption, as the hypoxia-inducible factor 1α is probably a necessary component of the metabolic switch to aerobic glycolysis. FH=fumarate hydratase; SDH=succinate dehydrogenase; TCA=tricarboxylic acid.
European Urology Focus DOI: ( /j.euf )
Copyright © Terms and Conditions

6. Fig. 5
Interaction between metabolic and epigenetic regulation in hypoxia. (A) α-ketoglutarate (α-KG) is produced in the TCA cycle, and its availability likely has an effect on enzymes that impact epigenetic and metabolic regulation. Fe– and α-KG–dependent dioxygenases are a large group of catalytically diverse, oxygen-activated enzymes that oxidize their substrate using α-KG as a cosubstrate. Many of these enzymes possess additional catalytic activity that links their well-established epigenetic role to metabolic regulation. (B) Besides dioxygenases, the SWI/SNF complex activity is intertwined with metabolism. Members of the yeast SWI/SNF complex had been isolated by a mutation screen that enabled yeast to switch from glucose to the alternative carbon source. ARID1A and ARID1B are the orthologs of the yeast Snf1. SWI/SNF activity has a double metabolic input: the presence of glucose and AMPK. RAG1 is a glucose transporter that participates in SWI/SNF activation. AMPK forms a complex with SNF1 and might also be directly regulated by AMP and ADP levels. SWI/SNF is an ATP-dependent chromatin remodeling complex and has a major consequence on genome-wide transcription. It has also been suggested that it coordinates glycolysis and glucose transport in yeast. Aerob=aerobic; ATP=adenosine triphosphate; TCA=tricarboxylic acid; SWI/SNF=switch/sucrose nonfermentable, ARID1A and ARID1B=AT-rich interaction domain 1A and 1B; AMPK=AMP-activated protein kinase; PHD=zinc fingers, prolyl hydroxylase domain type; TET=ten–eleven translocation methylcytosine dioxygenase family; JMJD=Jumonji domain containing protein family; HIF=hypoxia-inducible factor.
European Urology Focus DOI: ( /j.euf )
Copyright © Terms and Conditions