Inhibition of Lon protease by triterpenoids alters mitochondria and is associated to cell death in human cancer cells

// Lara Gibellini 1, * , Marcello Pinti 2, * , Regina Bartolomeo 1 , Sara De Biasi 1 , Antonella Cormio 3 , Clara Musicco 4 , Gianluca Carnevale 1 , Simone Pecorini 1 , Milena Nasi 1 , Anto De Pol 1 , Andrea Cossarizza 1 1 Department of Surgery, Medicine, Dentistry and Morphological Sciences, University of Modena and Reggio Emilia, Modena, Italy 2 Department of Life Sciences, University of Modena and Reggio Emilia, Modena, Italy 3 Department of Bioscience, Biotechnology and Biopharmaceutics, University of Bari, Bari, Italy 4 CNR – Institute of Biomembranes and Bioenergetics, Bari, Italy * These authors have contributed equally to this work Correspondence to: Marcello Pinti, e-mail: marcello.pinti@unimore.it Keywords: mitochondria, Lon, CDDO, CDDO-Me Received: January 28, 2015      Accepted: July 03, 2015      Published: July 15, 2015 ABSTRACT Mitochondrial Lon protease (Lon) regulates several mitochondrial functions, and is inhibited by the anticancer molecule triterpenoid 2-cyano-3, 12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO), or by its C-28 methyl ester derivative (CDDO-Me). To analyze the mechanism of action of triterpenoids, we investigated intramitochondrial reactive oxygen species (ROS), mitochondrial membrane potential, mitochondrial mass, mitochondrial dynamics and morphology, and Lon proteolytic activity in RKO human colon cancer cells, in HepG2 hepatocarcinoma cells and in MCF7 breast carcinoma cells. We found that CDDO and CDDO-Me are potent stressors for mitochondria in cancer cells, rather than normal non-transformed cells. In particular, they: i) cause depolarization; ii) increase mitochondrial ROS, iii) alter mitochondrial morphology and proteins involved in mitochondrial dynamics; iv) affect the levels of Lon and those of aconitase and human transcription factor A, which are targets of Lon activity; v) increase level of protein carbonyls in mitochondria; vi) lead to intrinsic apoptosis. The overexpression of Lon can rescue cells from cell death, providing an additional evidence on the role of Lon in conditions of excessive stress load.