Pyruvate dehydrogenase complex activity controls metabolic and malignant phenotype in cancer cells.

High lactate generation and low glucose oxidation, despite normal oxygen conditions, are commonly seen in cancer cells and tumors. Historically known as the Warburg effect, this altered metabolic phenotype has long been correlated with malignant progression and poor clinical outcome. However, the mechanistic relationship between altered glucose metabolism and malignancy remains poorly understood. Here we show that inhibition of pyruvate dehydrogenase complex (PDC) activity contributes to the Warburg metabolic and malignant phenotype in human head and neck squamous cell carcinoma. PDC inhibition occurs via enhanced expression of pyruvate dehydrogenase kinase-1 (PDK-1), which results in inhibitory phosphorylation of the pyruvate dehydrogenase alpha (PDHalpha) subunit. We also demonstrate that PDC inhibition in cancer cells is associated with normoxic stabilization of the malignancy-promoting transcription factor hypoxia-inducible factor-1alpha (HIF-1alpha) by glycolytic metabolites. Knockdown of PDK-1 via short hairpin RNA lowers PDHalpha phosphorylation, restores PDC activity, reverts the Warburg metabolic phenotype, decreases normoxic HIF-1alpha expression, lowers hypoxic cell survival, decreases invasiveness, and inhibits tumor growth. PDK-1 is an HIF-1-regulated gene, and these data suggest that the buildup of glycolytic metabolites, resulting from high PDK-1 expression, may in turn promote HIF-1 activation, thus sustaining a feed-forward loop for malignant progression. In addition to providing anabolic support for cancer cells, altered fuel metabolism thus supports a malignant phenotype. Correction of metabolic abnormalities offers unique opportunities for cancer treatment and may potentially synergize with other cancer therapies.

Role of protein-water interactions and electrostatics in alpha-synuclein fibril formation.

Deposition of misfolded alpha-synuclein is a critical factor in several neurodegenerative disorders. Filamentous alpha-synuclein is the major component of Lewy bodies and Lewy neurites, the intracellular inclusions in the dopaminergic neurons of the substantia nigra, which are considered the pathological hallmark of Parkinson's disease. We show here that anions induce partial folding of alpha-synuclein at neutral pH, forming a critical amyloidogenic intermediate, which leads to significant acceleration of the rate of fibrillation. The magnitude of the accelerating effect generally followed the position of the anions in the Hofmeister series, indicating a major role of protein-water-anion interactions in the process at salt concentrations above 10 mM. Below this concentration, electrostatic effects dominated in the mechanism of anion-induced fibrillation. The acceleration of fibrillation by anions was also dependent on the cation. Moderate concentrations of anions affected both the rates of nucleation and the elongation of alpha-synuclein fibrillation, primarily via their effect on the interaction of the protein with water.