Valeria G. Antico Arciuch

Mitochondrial Regulation of Cell Cycle and Proliferation

Eukaryotic mitochondria resulted from symbiotic incorporation of α-proteobacteria into ancient archaea species. During evolution, mitochondria lost most of the prokaryotic bacterial genes and only conserved a small fraction including those encoding 13 proteins of the respiratory chain. In this process, many functions were transferred to the host cells, but mitochondria gained a central role in the regulation of cell proliferation and apoptosis, and in the modulation of metabolism; accordingly, defective organelles contribute to cell transformation and cancer, diabetes, and neurodegenerative diseases. Most cell and transcriptional effects of mitochondria depend on the modulation of respiratory rate and on the production of hydrogen peroxide released into the cytosol. The mitochondrial oxidative rate has to remain depressed for cell proliferation; even in the presence of O₂, energy is preferentially obtained from increased glycolysis (Warburg effect). In response to stress signals, traffic of pro- and antiapoptotic mitochondrial proteins in the intermembrane space (B-cell lymphoma-extra large, Bcl-2-associated death promoter, Bcl-2 associated X-protein and cytochrome c) is modulated by the redox condition determined by mitochondrial O₂ utilization and mitochondrial nitric oxide metabolism. In this article, we highlight the traffic of the different canonical signaling pathways to mitochondria and the contributions of organelles to redox regulation of kinases. Finally, we analyze the dynamics of the mitochondrial population in cell cycle and apoptosis.

Mitochondrial Nitric Oxide Synthase: A Masterpiece of Metabolic Adaptation, Cell Growth, Transformation, and Death

Mitochondria are specialized organelles that control energy metabolism and also activate a multiplicity of pathways that modulate cell proliferation and mitochondrial biogenesis or, conversely, promote cell arrest and programmed cell death by a limited number of oxidative or nitrative reactions. Nitric oxide (NO) regulates oxygen uptake by reversible inhibition of cytochrome oxidase and the production of superoxide anion from the mitochondrial electron transfer chain. In this sense, NO produced by mtNOS will set the oxygen uptake level and contribute to oxidation-reduction reaction (redox)–dependent cell signaling. Modulation of translocation and activation of neuronal nitric oxide synthase (mtNOS activity) under different physiologic or pathologic conditions represents an adaptive response properly modulated to adjust mitochondria to different cell challenges.

Hypothyroid phenotype is contributed by mitochondrial complex I inactivation due to translocated neuronal nitric-oxide synthase.

Although transcriptional effects of thyroid hormones have substantial influence on oxidative metabolism, how thyroid sets basal metabolic rate remains obscure. Compartmental localization of nitric-oxide synthases is important for nitric oxide signaling. We therefore examined liver neuronal nitric-oxide synthase-α (nNOS) subcellular distribution as a putative mechanism for thyroid effects on rat metabolic rate. At low 3,3′,5-triiodo-l-thyronine levels, nNOS mRNA increased by 3-fold, protein expression by one-fold, and nNOS was selectively translocated to mitochondria without changes in other isoforms. In contrast, under thyroid hormone administration, mRNA level did not change and nNOS remained predominantly localized in cytosol. In hypothyroidism, nNOS translocation resulted in enhanced mitochondrial nitric-oxide synthase activity with low O2 uptake. In this context, NO utilization increased active O2 species and peroxynitrite yields and tyrosine nitration of complex I proteins that reduced complex activity. Hypothyroidism was also associated to high phospho-p38 mitogen-activated protein kinase and decreased phospho-extracellular signal-regulated kinase 1/2 and cyclin D1 levels. Similarly to thyroid hormones, but without changing thyroid status, nitric-oxide synthase inhibitor Nω-nitro-l-arginine methyl ester increased basal metabolic rate, prevented mitochondrial nitration and complex I derangement, and turned mitogen-activated protein kinase signaling and cyclin D1 expression back to control pattern. We surmise that nNOS spatial confinement in mitochondria is a significant downstream effector of thyroid hormone and hypothyroid phenotype.

Akt1 Intramitochondrial Cycling Is a Crucial Step in the Redox Modulation of Cell Cycle Progression

Akt is a serine/threonine kinase involved in cell proliferation, apoptosis, and glucose metabolism. Akt is differentially activated by growth factors and oxidative stress by sequential phosphorylation of Ser473 by mTORC2 and Thr308 by PDK1. On these bases, we investigated the mechanistic connection of H2O2 yield, mitochondrial activation of Akt1 and cell cycle progression in NIH/3T3 cell line with confocal microscopy, in vivo imaging, and directed mutagenesis. We demonstrate that modulation by H2O2 entails the entrance of cytosolic P-Akt1 Ser473 to mitochondria, where it is further phosphorylated at Thr308 by constitutive PDK1. Phosphorylation of Thr308 in mitochondria determines Akt1 passage to nuclei and triggers genomic post-translational mechanisms for cell proliferation. At high H2O2, Akt1-PDK1 association is disrupted and P-Akt1 Ser473 accumulates in mitochondria in detriment to nuclear translocation; accordingly, Akt1 T308A is retained in mitochondria. Low Akt1 activity increases cytochrome c release to cytosol leading to apoptosis. As assessed by mass spectra, differential H2O2 effects on Akt1-PDK interaction depend on the selective oxidation of Cys310 to sulfenic or cysteic acids. These results indicate that Akt1 intramitochondrial-cycling is central for redox modulation of cell fate.

Tumor Cell Phenotype Is Sustained by Selective MAPK Oxidation in Mitochondria

Mitochondria are major cellular sources of hydrogen peroxide (H2O2), the production of which is modulated by oxygen availability and the mitochondrial energy state. An increase of steady-state cell H2O2 concentration is able to control the transition from proliferating to quiescent phenotypes and to signal the end of proliferation; in tumor cells thereby, low H2O2 due to defective mitochondrial metabolism can contribute to sustain proliferation. Mitogen-activated protein kinases (MAPKs) orchestrate signal transduction and recent data indicate that are present in mitochondria and regulated by the redox state. On these bases, we investigated the mechanistic connection of tumor mitochondrial dysfunction, H2O2 yield, and activation of MAPKs in LP07 murine tumor cells with confocal microscopy, in vivo imaging and directed mutagenesis. Two redox conditions were examined: low 1 µM H2O2 increased cell proliferation in ERK1/2-dependent manner whereas high 50 µM H2O2 arrested cell cycle by p38 and JNK1/2 activation. Regarding the experimental conditions as a three-compartment model (mitochondria, cytosol, and nuclei), the different responses depended on MAPKs preferential traffic to mitochondria, where a selective activation of either ERK1/2 or p38-JNK1/2 by co-localized upstream kinases (MAPKKs) facilitated their further passage to nuclei. As assessed by mass spectra, MAPKs activation and efficient binding to cognate MAPKKs resulted from oxidation of conserved ERK1/2 or p38-JNK1/2 cysteine domains to sulfinic and sulfonic acids at a definite H2O2 level. Like this, high H2O2 or directed mutation of redox-sensitive ERK2 Cys214 impeded binding to MEK1/2, caused ERK2 retention in mitochondria and restricted shuttle to nuclei. It is surmised that selective cysteine oxidations adjust the electrostatic forces that participate in a particular MAPK-MAPKK interaction. Considering that tumor mitochondria are dysfunctional, their inability to increase H2O2 yield should disrupt synchronized MAPK oxidations and the regulation of cell cycle leading cells to remain in a proliferating phenotype.

Mitochondrial nitric oxide synthase drives redox signals for proliferation and quiescence in rat liver development

Mitochondrial nitric oxide synthase (mtNOS) is a fine regulator of oxygen uptake and reactive oxygen species that eventually modulates the activity of regulatory proteins and cell cycle progression. From this perspective, we examined liver mtNOS modulation and mitochondrial redox changes in developing rats from embryonic days 17–19 and postnatal day 2 (proliferating hepatocyte phenotype) through postnatal days 15–90 (quiescent phenotype). mtNOS expression and activity were almost undetectable in fetal liver, and progressively increased after birth by tenfold up to adult stage. NO‐dependent mitochondrial hydrogen peroxide (H2O2) production and Mn‐superoxide dismutase followed the developmental modulation of mtNOS and contributed to parallel variations of cytosolic H2O2 concentration ([H2O2]ss) and cell fluorescence. mtNOS‐dependent [H2O2]ss was a good predictor of extracellular signal–regulated kinase (ERK)/p38 activity ratio, cyclin D1, and tissue proliferation. At low 10−11–10−12 M [H2O2]ss, proliferating phenotypes had high cyclin D1 and phospho‐ERK1/2 and low phospho‐p38 mitogen‐activated protein kinase, while at 10−9 M [H2O2]ss, quiescent phenotypes had the opposite pattern. Accordingly, leading postnatal day 2–isolated hepatocytes to embryo or adult redox conditions with H2O2 or NO‐H2O2 scavengers, or with ERK inhibitor U0126, p38 inhibitor SB202190 or p38 activator anisomycin resulted in correlative changes of ERK/p38 activity ratio, cyclin D1 expression, and [3H] thymidine incorporation in the cells. Accordingly, p38 inhibitor SB202190 or N‐acetyl‐cysteine prevented H2O2 inhibitory effects on proliferation. In conclusion, the results suggest that a synchronized increase of mtNOS and derived H2O2 operate on hepatocyte signaling pathways to support the liver developmental transition from proliferation to quiescence. (HEPATOLOGY 2004;40:157–166.)

Mitochondrial kinases in cell signaling: Facts and perspectives.

Phylogenetic studies had shown that evolution of mitochondria occurred in parallel with the maturation of kinases implicated in growth and final size of modern organisms. In the last years, different reports confirmed that MAPKs, Akt, PKA and PKC are present in mitochondria, particularly in the intermembrane space and inner membrane where they meet mitochondrial constitutive upstream activators. Although a priori phosphorylation is the apparent aim of translocation, new perspectives indicate that kinase activation depends on redox status as determined by the mitochondrial production of oxygen species. We observed that the degree of mitochondrial oxidation of ERK Cys(38) and Cys(214) discriminates the kinase to be phosphorylated and determines translocation to the nuclear compartment and proliferation, or accumulation in mitochondria and arrest. Otherwise, transcriptional gene regulation by Akt depends on Cys(60) and Cys(310) oxidation to sulfenic and sulfonic acids. It is concluded that the interactions between kinases and mitochondria control cell signaling pathways and participate in the modulation of cell proliferation and arrest, tissue protection, tumorigenesis and cancer progression.

Abstract A019: Heme-oxygenase 1 drives the metabolic fate in prostate cancer

Prostate cancer (PCa) is the second leading cause of cancer-associated death in men. Energetic metabolism alterations have become a new hallmark of cancer, since variations in a single gene can orchestrate changes in metabolic pathways and confer an adaptive advantage. Heme-oxygenase 1 (HO-1) exerts an antitumoral role in PCa inhibiting cell proliferation, migration, tumor growth, and angiogenesis. The aim of this work was to assess the role of HO-1 in the metabolic signature of PCa. Through RNA-Seq we found a set of metabolic genes deregulated under pharmacologic induction (hemin treatment) or genetic induction of HO-1 in PC3 cells. STAR and ATP5L2 were upregulated, while HMGCS2, PRODH, and ACOT12 were downregulated. These genes encode for steroid hormone metabolism, ATP synthesis, ketogenesis, proline and lipid metabolism. The analysis of the deregulated genes (2-fold) by Gene Ontology revealed alterations in several metabolic pathways such as steroid, proline and lipid metabolism, and ATP synthesis. Functional analysis highlighted a decrease in oxygen consumption rate and ATP production under hemin treatment. Furthermore, HO-1 induction led to a decrease in the extracellular lactate levels. Bone is the only site of PCa progression, and bone cells are able to produce factors that favor progression. However, the molecular nature of this interaction remains elusive. Our results performed on cocultures of PC3 cells (treated or not with hemin) with Raw264.7 (preosteoclastic) or MC3T3 (preosteoblastic) cells demonstrate that HO-1 directs the metabolic fate of bone precursor cells due to the deregulation of glycolytic genes. HO-1 induction in PC3 cells downregulated PKM2 and LDHA expression in cocultured Raw264.7 and MC3T3 cells (p Based on our results, we propose HO-1 as a key regulator of the metabolic status of PCa cells and a powerful mediator capable of redefining the metabolic signature of bone precursor cells, thus favoring the establishment of a less aggressive phenotype. Citation Format: Valeria G. Antico Arciuch, Florencia Cascardo, Florencia Velazquez, Sofia Lage Vickers, Nicolas Anselmino, Estefania Labanca, Javier Cotignola, Geraldine Gueron, Nora Navone, Elba Vazquez. Heme-oxygenase 1 drives the metabolic fate in prostate cancer [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr A019.