Frontiers in Oncology (Apr 2020)

Physiological Role of Glutamate Dehydrogenase in Cancer Cells

  • Rafael Moreno-Sánchez,
  • Álvaro Marín-Hernández,
  • Juan C. Gallardo-Pérez,
  • Silvia C. Pacheco-Velázquez,
  • Diana X. Robledo-Cadena,
  • Joaquín Alberto Padilla-Flores,
  • Emma Saavedra,
  • Sara Rodríguez-Enríquez

DOI
https://doi.org/10.3389/fonc.2020.00429
Journal volume & issue
Vol. 10

Abstract

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NH4+ increased growth rates and final densities of several human metastatic cancer cells. To assess whether glutamate dehydrogenase (GDH) in cancer cells may catalyze the reverse reaction of NH4+ fixation, its covalent regulation and kinetic parameters were determined under near-physiological conditions. Increased total protein and phosphorylation were attained in NH4+-supplemented metastatic cells, but total cell GDH activity was unchanged. Higher Vmax values for the GDH reverse reaction vs. forward reaction in both isolated hepatoma (HepM) and liver mitochondria [rat liver mitochondria (RLM)] favored an NH4+-fixing role. GDH sigmoidal kinetics with NH4+, ADP, and leucine fitted to Hill equation showed nH values of 2 to 3. However, the K0.5 values for NH4+ were over 20 mM, questioning the physiological relevance of the GDH reverse reaction, because intracellular NH4+ in tumors is 1 to 5 mM. In contrast, data fitting to the Monod–Wyman–Changeux (MWC) model revealed lower Km values for NH4+, of 6 to 12 mM. In silico analysis made with MWC equation, and using physiological concentrations of substrates and modulators, predicted GDH N-fixing activity in cancer cells. Therefore, together with its thermodynamic feasibility, GDH may reach rates for its reverse, NH4+-fixing reaction that are compatible with an anabolic role for supporting growth of cancer cells.

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