Adenine nucleotides transport across the inner mitochondrial membrane in cancer cells: role of ANTs and SCaMCs
Authors:   Dept. Biología Molecular, Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones CientíficasUniversidad Autónoma de Madrid (CSIC-UAM), Madrid, Spain. Instituto de Investigación Sanitaria Fundación Jiménez Díaz (IIS-FJD), 28049 Madrid, Spain., González-Moreno Luis , Juaristi Inés ,   Dept. Biología Molecular, Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones CientíficasUniversidad Autónoma de Madrid (CSIC-UAM), Madrid, Spain. Instituto de Investigación Sanitaria Fundación Jiménez Díaz (IIS-FJD), 28049 Madrid, Spain., Satrústegui Jorgina ,   Dept. Biología Molecular, Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones CientíficasUniversidad Autónoma de Madrid (CSIC-UAM), Madrid, Spain. Instituto de Investigación Sanitaria Fundación Jiménez Díaz (IIS-FJD), 28049 Madrid, Spain., del Arco Araceli ,   Dept. Biología Molecular, Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones CientíficasUniversidad Autónoma de Madrid (CSIC-UAM), Madrid, Spain. Instituto de Investigación Sanitaria Fundación Jiménez Díaz (IIS-FJD), 28049 Madrid, Spain.,   2Facultad de Ciencias Ambientales y Bioquímica, Universidad de Castilla la Mancha, Toledo, Spain. Centro Regional de Investigaciones Biomédicas, Unidad Asociada de Biomedicina UCLM-CSIC, 45071 Toledo, Spain.
Published: June 2022

Introduction: The regulation of adenine nucleotide levels in the mitochondria and the cytosol is essential for cell metabolism. To sustain mitochondrial respiration, ATP generated by ATP synthase must be exported to the cytosol, whereas mitochondria must be refilled with ADP and Pi. Adenine Nucleotide Translocases (ANTs), which catalyze the electrogenic ATP4-/ADP3- exchange, have been proposed to work together with ATP synthase and the mitochondrial phosphate carrier to support mitochondrial oxidative phosphorylation by forming the so-called ATP synthasome. Nevertheless, disruption of the main ANT isoform or pharmacological inhibition of ANTs in cancer cells does not decrease oxidative phosphorylation. Furthermore, the import of cytosolic ATP to the mitochondria when oxidative phosphorylation is inhibited (required, for example, for the maintenance of the ΔΨm) is neither mediated by ANTs in cancer cells. Here, we study the possibility that calcium-regulated mitochondrial ATP-Mg2+/Pi or ADP/Pi carriers, (also called SCaMCs), might participate in the mitochondrial transport of adenine nucleotides in cancer cells. Material and methods: To study the function of SCaMC-1, the main isoform in cancer cells, we have generated SCaMC-1 KO HeLa cells using CRISPR-Cas9 genome editing. These cells have been characterized in terms of OCR (with Seahorse XF24), mitochondrial membrane potential (with TMRM) and mitochondrial ATP levels (with mitoGoATeam genetic probe) in basal conditions and in the presence of ETC inhibitors. Results and conclusions: We show that SCaMC-1, the isoform that is abundant in tumor cells, mediates ATP import to the mitochondria after histamine stimulation of HeLa cells, probably to buffer calcium entry to the mitochondria. However, SCaMC-1 does not participate in the transport of cytosolic ATP for the maintenance of ΔΨm after OXPHOS inhibition, neither decreases mitochondrial respiration. Future studies based on the deletion of the other SCaMCs isoforms (SCaMC-2, SCaMC-3, SCaMC-3 like) together with simultaneous deletion of ANTs and SCaMCs will be required to shed light on the control of adenine nucleotides transport between the mitochondria and the cytosol in cancer cells.