Lon upregulation contributes to cisplatin resistance by triggering NCLX-mediated mitochondrial Ca2+ release in cancer cells

Abstract

Mitochondria are the major organelles in sensing cellular stress and inducing the response for cell survival. Mitochondrial Lon has been identified as an important stress protein involved in regulating proliferation, metastasis, and apoptosis in cancer cells. However, the mechanism of retrograde signaling by Lon on mitochondrial DNA (mtDNA) damage remains to be elucidated. Here we report the role of Lon in the response to cisplatin-induced mtDNA damage and oxidative stress, which confers cancer cells on cisplatin resistance via modulating calcium levels in mitochondria and cytosol. First, we found that cisplatin treatment on oral cancer cells caused oxidative damage of mtDNA and induced Lon expression. Lon overexpression in cancer cells decreased while Lon knockdown sensitized the cytotoxicity towards cisplatin treatment. We further identified that cisplatin-induced Lon activates the PYK2-SRC-STAT3 pathway to stimulate Bcl-2 and IL-6 expression, leading to the cytotoxicity resistance to cisplatin. Intriguingly, we found that activation of this pathway is through an increase of intracellular calcium (Ca2+) via NCLX, a mitochondrial Na+/Ca2+ exchanger. We then verified that NCLX expression is dependent on Lon levels; Lon interacts with and activates NCLX activity. NCLX inhibition increased the level of mitochondrial calcium and sensitized the cytotoxicity to cisplatin in vitro and in vivo. In summary, mitochondrial Lon-induced cisplatin resistance is mediated by calcium release into cytosol through NCLX, which activates calcium-dependent PYK2-SRC-STAT3-IL-6 pathway. Thus, our work uncovers the novel retrograde signaling by mitochondrial Lon on resistance to cisplatin-induced mtDNA stress, indicating the potential use of Lon and NCLX inhibitors for better clinical outcomes in chemoresistant cancer patients.

Mitochondrial oxidative stress in the tumor microenvironment and cancer immunoescape: foe or friend?

“…As a cytoprotective chaperone, Lon interacts with Hsp60-mtHsp70 complex [ 82 ] and sequesters p53 [ 83 ] in mitochondria matrix to restrain apoptosis. A recent study also showed that the resistance mechanism by Lon interacting with NCLX inhibits excess mitochondrial calcium influx induced by cisplatin to trigger cell death [ 84 ]. Lon also participates in cysteine metabolism to repress lipid peroxidative in regulating ferroptosis [ 85 ].…”

“…MAMs contains ER-localized IP3R/RyR receptors, SERCA pumps, mitochondrial Voltage-dependent anion channel (VDAC), and the mitochondrial Ca 2+ uniporter (MCU) in the outer and inner mitochondrial membrane [ 111 ]. To avoid the lethal cell death triggered by mtROS, cells set up the preventive mechanism to neutralize the mitochondria generated ROS through activation of mitophagy, release of mitochondrial calcium through NCLX efflux channel [ 84 ], MnSOD enzymatic dismutation [ 112 , 113 ]. Taken together, it is important that, for the normal function of mitochondria Ca 2+ and ROS homeostasis are very signification, a little dynamic alterations or imbalance in calcium leads to different consequences on cellular function especially during pathophysiological process.…”

“…In addition, HIF1α is a key stimulator to induce upregulation of mitochondrial Lon that generates ROS [ 48 ]. A recent study also indicated that under cisplatin treatment, IL-6 secretion promoted by STAT3 signaling is dependent on Lon-induced increase in intracellular ROS and calcium [ 84 ]. Therefore, the positive feedback of Lon-induced ROS via NF-kB axis enhanced downstream signaling to promote tumor progression.…”

“…In addition, mtDNA is vulnerable to damage by ROS and the mtDNA mutations play a role in chemotherapy resistance [220,221]. The cisplatin resistant cancer cells showed mtDNA mutations and elevated ROS thereby activating NF-κB mediated inhibitor of apoptotic proteins and Ca 2+ -dependent inflammation [84,222].…”

Roles of LonP1 in Oral-Maxillofacial Developmental Defects and Tumors: A Novel Insight

“…An association has also been noted between NCLX and LonP1 levels in oral cancer tissue samples. Inhibitors of LonP1 and NCLX may be used as potential adjuvants to cisplatin therapy to avoid chemoresistance and enhance the curative effect in patients with oral cancer [ 87 ].…”