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Reply to Beltinger: Double genetic disruption of lactate dehydrogenases A and B is required to ablate the “Warburg effect” restricting tumor growth to oxidative metabolism

Open AccessPublished:January 01, 2019DOI:https://doi.org/10.1074/jbc.RL118.006868
      We thank Christian Beltinger (
      • Beltinger C.
      LDHA and LDHB are dispensable for aerobic glycolysis in neuroblastoma cells while promoting their aggressiveness.
      ) for bringing to our attention an interesting and similar story conducted in neuroblastoma cell lines. Although the recognition that both independent studies (
      • Ždralević M.
      • Brand A.
      • Di Ianni L.
      • Dettmer K.
      • Reinders J.
      • Singer K.
      • Peter K.
      • Schnell A.
      • Bruss C.
      • Decking S.-M.
      • Koehl G.
      • Felipe-Abrio B.
      • Durivault J.
      • Bayer P.
      • Evangelista M.
      • O'Brien T.
      • Oefner P.J.
      • Renner K.
      • Pouysségur J.
      • Kreutz M.
      (2018) Double genetic disruption of lactate dehydrogenases A and B is required to ablate the “Warburg effect” restricting tumor growth to oxidative metabolism.
      ,
      • Dorneburg C.
      • Fischer M.
      • Barth T.F.E.
      • Mueller-Klieser W.
      • Hero B.
      • Gecht J.
      • Carter D.R.
      • de Preter K.
      • Mayer B.
      • Christner L.
      • Speleman F.
      • Marshall G.M.
      • Debatin K.M.
      • Beltinger C.
      LDHA in neuroblastoma is associated with poor outcome and its depletion decreases neuroblastoma growth independent of aerobic glycolysis.
      ) conclude that glycolysis is dispensable for tumor growth, Christian Beltinger raised contrasting findings: “In contrast to the results of Ždralević et al., however, concomitant depletion of LDHA and LDHB in neuroblastoma cells did not abrogate the Warburg effect.” Our answer is that in Beltinger's study LDHB is not fully depleted by doxycycline-induced shRNA. Indeed, we previously experienced that a 90% knockdown of glucose-6-phosphate isomerase (GPI) activity did not alter the rate of glycolysis. Only a complete GPI-KO abrogated the Warburg effect (
      • de Padua M.C.
      • Delodi G.
      • Vučetić M.
      • Durivault J.
      • Vial V.
      • Bayer P.
      • Noleto G.R.
      • Mazure N.M.
      • Ždralević M.
      • Pouysségur J.
      Disrupting glucose-6-phosphate isomerase fully suppresses the “Warburg effect” and activates OXPHOS with minimal impact on tumor growth except in hypoxia.
      ). We therefore presume that the residual LDHB activity in LDHA-KO/LDHB-KD cell lines of Beltinger's study is higher than actually reported, which could be shown if the enzymatic assay was performed with the substrates of the LDHB reaction (lactate + NAD+). A second contrasting point in our two studies is complete clonogenicity suppression of LDHA-KO/LDHB-KD neuroblastoma cell lines, which was not observed in our LDHA/B-DKO Warburg effect–ablated cells in normoxia.
      The use of doxycycline to induce shLDHB expression is problematic because it compromises mitochondrial function (
      • Chatzispyrou I.A.
      • Held N.M.
      • Mouchiroud L.
      • Auwerx J.
      • Houtkooper R.H.
      Tetracycline antibiotics impair mitochondrial function and its experimental use confounds research.
      ). This is particularly relevant in this study, where functional OXPHOS is essential when glycolysis is reduced or ablated.

      References

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        • O'Brien T.
        • Oefner P.J.
        • Renner K.
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