Summary The lactate dehydrogenase-A (LDH-A) enzyme catalyzes the inter-conversion of pyruvate and lactate, is upregulated in human cancers and is associated with aggressive tumor outcomes. Here we use a novel inducible murine model and demonstrate that inactivation of LDH-A in mouse models of NSCLC driven by oncogenic K-RAS or EGFR leads to decreased tumorigenesis and disease regression in established tumors. We also show that abrogation of LDH-A results in reprogramming of pyruvate metabolism, with decreased lactic fermentation in vitro, in vivo, and ex vivo. This was accompanied by re-activation of mitochondrial function in vitro but not in vivo or ex vivo. Finally, using a specific small molecule LDH-A inhibitor, we demonstrated that LDH-A is essential for cancer initiating cell survival and proliferation. Thus, LDH-A can be a viable therapeutic target for NSCLC including cancer stem cell-dependent drug resistant tumors.

SUMMARY Mutations in the metabolic enzymes isocitrate dehydrogenase-1 (IDH1) and IDH2 that produce the oncometabolite D-2-hydroxyglutarate (2-HG) occur frequently in human acute myeloid leukemia (AML). 2-HG modulates numerous biological pathways implicated in malignant transformation, but the contribution of mutant IDH proteins to maintenance and progression of AML in vivo is currently unknown. To answer this crucial question we have generated transgenic mice that express IDH2R140Q in an on/ off- and tissue-specific manner using a tetracycline-inducible system. We found that IDH2R140Q can cooperate with overexpression of HoxA9 and Meis1a and with mutations in FMS-like tyrosine kinase 3 (FLT3) to drive acute leukemia in vivo. Critically, we show that genetic deinduction of mutant IDH2 in leukemic cells in vivo has profound effects on their growth and/or maintenance. Our data demonstrate the proto-oncogenic role of mutant IDH2 and support its relevance as a therapeutic target for the treatment of human AML.

Welle S, Burgess K, Mehta S. Stimulation of skeletal muscle myofibrillar protein synthesis, p70 S6 kinase phosphorylation, and ribosomal protein S6 phosphorylation by inhibition of myostatin in mature mice. Am J Physiol Endocrinol Metab 296: E567-E572, 2009. First published January 13, 2009; doi:10.1152/ajpendo.90862.2008.-Knocking out myostatin activity during development increases the rate of muscle protein synthesis. The present study was done to determine whether postdevelopmental loss of myostatin activity stimulates myofibrillar protein synthesis and the phosphorylation of some of the proteins involved in regulation of protein synthesis rate. Myostatin activity was inhibited for 4 days, in 4-to 5-mo-old male mice, with injections of an anti-myostatin antibody (JA16). The mean myofibrillar synthesis rate increased 19% (P Ͻ 0.01) relative to the mean rate in saline-treated mice, as determined by incorporation of deuterium-labeled phenylalanine. JA16 increased phosphorylation of p70 S6 kinase (S6K) and ribosomal protein S6 (rpS6) 1.9-fold (P Ͻ 0.05). It did not affect phosphorylation of eukaryotic initiation factor 4E-binding protein-1 or Akt. Microarrays and realtime PCR analyses indicated that JA16 administration did not selectively enrich levels of mRNAs encoding myofibrillar proteins, ribosomal proteins, or translation initiation and elongation factors. Rapamycin treatment did not affect the rate of myofibrillar protein synthesis whether or not the mice received JA16 injections, although it eliminated the phosphorylation of S6K and rpS6. We conclude that the normal level of myostatin activity in mature muscle is sufficient to inhibit myofibrillar synthesis rate and phosphorylation of S6K and rpS6. Reversal of the inhibition of myofibrillar synthesis with an anti-myostatin antibody is not dependent on mTOR activation. rapamycin; mammalian target of rapamycin; Akt; eukaryotic initiation factor 4E-binding protein-1; translation; JA16 anti-myostatin antibody GENETIC MUTATIONS CAUSING LOSS of myostatin activity lead to marked hypermuscularity in several mammalian species, including humans (3,12,13,19,20). When myostatin activity is inhibited in mice several weeks or months after birth, there is a more modest muscle growth (2, 9, 23, 26 -28). The postdevelopmental effects of myostatin are of great interest with respect to potential clinical applications of myostatin inhibitors. The early responses to myostatin inhibition are important in understanding the mechanism of hypertrophy and could be useful biomarkers for preclinical or initial clinical trials of the efficacy of potential anti-myostatin agents. Thus the present study was done to search for early molecular changes in adult skeletal muscle after inhibition of myostatin activity with an anti-myostatin antibody.For muscle fiber enlargement to be functionally useful, the mass of myofibrils must increase along with the overall muscle size. Increased myofibrillar mass can occur only if the rate of myofibrillar synthesis exceeds the rate of degradation. In cul...

We compared the growth, phenology and leaf demography of partly defoliated, connected shoots with that of partly defoliated, severed shoots in four old-field perennials (Solidago canadensis, S. altissima, S. gigantea, Aster lanceolatus) with differing genet architectures (rhizome systems), in a common garden and in the field. Our main hypothesis was that defoliation would have fewer negative effects on shoot performance if shoots were connected than if their rhizomes were severed. Since degree of clonal integration is related to differences in genet architecture, our second hypothesis was that the effects of defoliation would be less pronounced in more integrated than in less integrated clones. Removing about 50% of the total leaf area from shoots had different effects depending on plant species, shoot density, and in particular whether rhizome connections between shoots were left intact or severed. In agreement with our prediction, experimentally isolated shoots in the field or in high density clumps in the garden suffered the most from defoliation, while shoots with intact connections or in low density clumps suffered the least. Our second prediction was neither confirmed nor falsified in the present study. Solidago altissima showed overcompensation in response to simulated herbivory in the common garden, i.e. defoliated shoots grew faster and were larger at harvest than their non-defoliated neighbours.