Prolonged hypoxia decreases nuclear pyruvate dehydrogenase complex and regulates the gene expression.

Cells require proper regulation of energy metabolism to maintain cellular homeostasis. Pyruvate dehydrogenase (PDH) is a metabolic enzyme that converts pyruvate into acetyl-CoA, connecting glycolysis to the TCA cycle, thus regulating cellular energy metabolism. PDH is involved in multiple cellular processes, such as glucose metabolism, fatty acid synthesis, and protein acetylation, all of which are mediated by acetyl-CoA. We previously demonstrated that PDH-E1ß is downregulated in prolonged hypoxia and inhibits PDH activity, which serves as machinery to securely inhibit PDH activity together with PDH-E1α phosphorylation. PDH has been identified to localize to the nucleus in addition to mitochondria, but its precise regulatory mechanisms in the nucleus remain elusive. In the present study, we characterized nuclear PDH during prolonged hypoxia. Nuclear PDH complex was downregulated under hypoxic conditions, and PDH activity was reduced. Depletion of HIF-1α partly recovered nuclear levels of the PDH complex. Furthermore, decreased nuclear PDH activity resulted in reduced histone H3 acetylation, altering the gene expression profile of cells exposed to prolonged hypoxia. Taken together, these findings indicate that nuclear PDH complex is downregulated under prolonged hypoxic conditions and controls gene expression.

Pyruvate Dehydrogenase PDH-E1ß Controls Tumor Progression by Altering the Metabolic Status of Cancer Cells.

Downregulation of pyruvate dehydrogenase (PDH) is critical for the aberrant preferential activation of glycolysis in cancer cells under normoxic conditions. Phosphorylation-dependent inhibition of PDH is a relevant event in this process, but it is not durable as it relies on PDH kinases that are activated ordinarily under hypoxic conditions. Thus, it remains unclear how PDH is durably downregulated in cancer cells that are not hypoxic. Building on evidence that PDH activity depends on the stability of a multi-protein PDH complex, we found that the PDH-E1ß subunit of the PDH complex is downregulated to inhibit PDH activity under conditions of prolonged hypoxia. After restoration of normoxic conditions, reduced expression of PDH-E1ß was sustained such that glycolysis remained highly activated. Notably, PDH-E1ß silencing in cancer cells produced a metabolic state strongly resembling the Warburg effect, but inhibited tumor growth. Conversely, enforced exogenous expression of PDH-E1ß durably increased PDH activity and promoted the malignant growth of breast cancer cells in vivo Taken together, our results establish the specific mechanism through which PDH acts as an oncogenic factor by tuning glycolytic metabolism in cancer cells.Significance: This seminal study offers a mechanistic explanation for why glycolysis is aberrantly activated in normoxic cancer cells, offering insights into this long-standing hallmark of cancer termed the Warburg effect. Cancer Res; 78(7); 1592-603. ©2018 AACR.

Identification of Cereulide-Producing Bacillus cereus by Nucleic Acid Chromatography and Reverse Transcription Real-Time PCR.

RNA extracts were analyzed with a nucleic acid sequence-based amplification (NASBA) - nucleic acid chromatography and a reverse transcription-quantitative PCR assay (RT-qPCR) based on the TaqMan probe for identification of cereulide-producing Bacillus cereus. All 100 emetic B. cereus strains were found to give positive results, but 50 diarrheal B. cereus strains and other bacterial species showed negative results in the NASBA-chromatography. That is, the assay could selectively identify the emetic strains among B. cereus strains. Also, the B. cereus contents of more than 10(7) cfu/ml were required for the identification of the cereulide-producing strains in this assay. In qRT-PCR assays, all 100 emetic type strains of B. cereus produced 10(2) - 10(4) copy numbers per ng of the RNA preparation, and the strains produced 10(4) copies including ones which had the high vacuolation activities of HEp-2 cells.