Serine Catabolism by SHMT2 Is Required for Proper Mitochondrial Translation Initiation and Maintenance of Formylmethionyl-tRNAs.

Upon glucose restriction, eukaryotic cells upregulate oxidative metabolism to maintain homeostasis. Using genetic screens, we find that the mitochondrial serine hydroxymethyltransferase (SHMT2) is required for robust mitochondrial oxygen consumption and low glucose proliferation. SHMT2 catalyzes the first step in mitochondrial one-carbon metabolism, which, particularly in proliferating cells, produces tetrahydrofolate (THF)-conjugated one-carbon units used in cytoplasmic reactions despite the presence of a parallel cytoplasmic pathway. Impairing cytoplasmic one-carbon metabolism or blocking efflux of one-carbon units from mitochondria does not phenocopy SHMT2 loss, indicating that a mitochondrial THF cofactor is responsible for the observed phenotype. The enzyme MTFMT utilizes one such cofactor, 10-formyl THF, producing formylmethionyl-tRNAs, specialized initiator tRNAs necessary for proper translation of mitochondrially encoded proteins. Accordingly, SHMT2 null cells specifically fail to maintain formylmethionyl-tRNA pools and mitochondrially encoded proteins, phenotypes similar to those observed in MTFMT-deficient patients. These findings provide a rationale for maintaining a compartmentalized one-carbon pathway in mitochondria.

Role of NADH Dehydrogenase (Ubiquinone) 1 Alpha Subcomplex 4-Like 2 in Clear Cell Renal Cell Carcinoma.

PURPOSE: We delineated the functions of the hypoxia-inducible factor-1α (HIF1α) target NADH dehydrogenase (ubiquinone) 1 alpha subcomplex 4-like 2 (NDUFA4L2) in clear cell renal cell carcinoma (ccRCC) and characterized NDUFA4L2 as a novel molecular target for ccRCC treatment. EXPERIMENTAL DESIGN: We evaluated normal kidney and ccRCC patient microarray and RNAseq data from Oncomine and The Cancer Genome Atlas for NDUFA4L2 mRNA levels and the clinical implications of high NDUFA4L2 expression. In addition, we examined normal kidney and ccRCC patient tissue samples, human ccRCC cell lines, and murine models of ccRCC for NDUFA4L2 mRNA and protein expression. Utilizing short hairpin RNA, we performed NDUFA4L2 knockdown experiments and analyzed the proliferation, clonogenicity, metabolite levels, cell structure, and autophagy in ccRCC cell lines in culture. RESULTS: We found that NDUFA4L2 mRNA and protein are highly expressed in ccRCC samples but undetectable in normal kidney tissue samples, and that NDUFA4L2 mRNA expression correlates with tumor stage and lower overall survival. In addition, we demonstrated that NDUFA4L2 is an HIF1α target in ccRCC and that NDUFA4L2 knockdown has a profound antiproliferative effect, alters metabolic pathways, and causes major stress in cultured RCC cells. CONCLUSIONS: Collectively, our data show that NDUFA4L2 is a novel molecular target for ccRCC treatment. Clin Cancer Res; 22(11); 2791-801. ©2016 AACR.

Analyses of the transcriptome and metabolome demonstrate that HIF1α mediates altered tumor metabolism in clear cell renal cell carcinoma.

Hypoxia inducible factor 1 alpha (HIF1α) is a transcription factor that is frequently stabilized and active in human clear cell renal cell carcinoma (ccRCC). We have found that constitutively active HIF1α is sufficient to cause neoplastic transformation in a murine model of ccRCC termed the TRACK model. RNA sequencing (RNAseq) and untargeted metabolomics analyses of samples from TRACK kidneys demonstrate that HIF1α activates the transcription of genes that cause increased glucose uptake, glycolysis, and lactate production, as well as a decrease in the flux of pyruvate entering the tricarboxylic acid (TCA) cycle and a decrease in oxidative phosphorylation; these changes are identical to those observed in human ccRCC samples. These studies show that a constitutively active HIF1α promotes tumorigenesis in TRACK mice by mediating a metabolic switch to aerobic glycolysis, i.e., the Warburg effect, and suggest that TRACK mice are a valid model to test novel therapies targeting metabolic changes to inhibit human ccRCC.

Mesoscale nanoparticles selectively target the renal proximal tubule epithelium.

We synthesized "mesoscale" nanoparticles, approximately 400 nm in diameter, which unexpectedly localized selectively in renal proximal tubules and up to 7 times more efficiently in the kidney than other organs. Although nanoparticles typically localize in the liver and spleen, modulating their size and opsonization potential allowed for stable targeting of the kidneys through a new proposed uptake mechanism. Applying this kidney targeting strategy, we anticipate use in the treatment of renal disease and the study of renal physiology.

Genome-Wide Profiling of TRACK Kidneys Shows Similarity to the Human ccRCC Transcriptome.

UNLABELLED: Renal cell carcinoma (RCC) is the most common cancer arising from the kidney in adults, with clear cell RCC (ccRCC) representing the majority of all RCCs. Expression of a human HIF1α triple-mutant (P402A, P564A, and N803A) construct in the proximal tubule cells of C57BL/6 mice [TRAnsgenic model of Cancer of the Kidney (TRACK); ref. 1] mimics the histologic changes found in early stage human ccRCC. To better understand the genomic landscape, a high-throughput sequence analysis was performed with cDNA libraries (RNAseq) derived from TRACK transgenic positive (TG(+)) kidney cortex along with human ccRCC transcripts from the Oncomine and The Cancer Genome Atlas databases. Importantly, the expression profiles of TRACK TG(+) kidneys show significant similarities with those observed in human ccRCC, including increased expression of genes involved in glycolysis and the tricarboxylic acid cycle. Some of the transcripts overexpressed in both the TRACK mouse model and human ccRCC include ANKRD37, CA9, EGLN3, HK2, NDUFA4L2, and SLC16A3. These data suggest that constitutive activation of HIF1α in kidney proximal tubule cells transcriptionally reprograms the regulation of metabolic pathways in the kidney and that HIF1α is a major contributor to the altered metabolism observed in human ccRCC. IMPLICATIONS: TRACK (GGT-HIF1αM3) kidney mRNA profiles show similarities to human ccRCC transcriptome and phenotypes associated with the Warburg effect.

The role of HIF1α in renal cell carcinoma tumorigenesis.

UNLABELLED: The transcription factor HIF1α is implicated in the development of clear cell renal cell carcinoma (ccRCC). Although HIF1α was initially believed to be essential for ccRCC development, recent studies hypothesize an oncogenic role for HIF2α in ccRCC, but a tumor suppressor role for HIF1α, leading to uncertainty as to the precise roles of the different HIF transcription factors in this disease. Using evidence available from studies with human ccRCC cell lines, mouse xenografts, murine models of ccRCC, and human ccRCC specimens, we evaluate the roles of HIF1α and HIF2α in the pathogenesis of ccRCC. We present a convergence of clinical and mechanistic data supporting an important role for HIF1α in promoting tumorigenesis in a clinically important and large subset of ccRCC. This indicates that current understanding of the exact roles of HIF1α and HIF2α is incomplete and that further research is required to determine the diverse roles of HIF1α and HIF2α in ccRCC. KEY MESSAGES: The TRACK mouse ccRCC model with constitutively active HIF1α but not HIF2α expressed in proximal tubules develops RCC. HIF1α protein is expressed in the majority of human ccRCC specimens. Elevated HIF1α in ccRCC correlates with a worse prognosis. Many publications do not support a tumor suppressor role for HIF1α in ccRCC. HIF1α, but not HIF2α, is expressed in some types of cancer stem cells.