Physiological Role of Glutamate Dehydrogenase in Cancer Cells.

Abstract

NH 4 + 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 NH 4 + fixation, its covalent regulation and kinetic parameters were determined under near-physiological conditions. Increased total protein and phosphorylation were attained in NH 4 + -supplemented metastatic cells, but total cell GDH activity was unchanged. Higher V max values for the GDH reverse reaction vs. forward reaction in both isolated hepatoma (HepM) and liver mitochondria [rat liver mitochondria (RLM)] favored an NH 4 + -fixing role. GDH sigmoidal kinetics with NH 4 + , ADP, and leucine fitted to Hill equation showed n H values of 2 to 3. However, the K 0.5 values for NH 4 + were over 20 mM, questioning the physiological relevance of the GDH reverse reaction, because intracellular NH 4 + in tumors is 1 to 5 mM. In contrast, data fitting to the Monod-Wyman-Changeux (MWC) model revealed lower K m values for NH 4 + , 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, NH 4 + -fixing reaction that are compatible with an anabolic role for supporting growth of cancer cells.

• Authors: 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
• Journal: Frontiers in oncology (Front Oncol) Vol. 10 Pg. 429 ( 2020) ISSN: 2234-943X [Print] Switzerland
• PMID: 32328457 (Publication Type: Journal Article)
• Copyright: Copyright © 2020 Moreno-Sánchez, Marín-Hernández, Gallardo-Pérez, Pacheco-Velázquez, Robledo-Cadena, Padilla-Flores, Saavedra and Rodríguez-Enríquez.