bims-mibica 2024-08-25 papers

bims-mibica

Biomed News

on Mitochondrial bioenergetics in cancer

Issue of 2024–08–25
eightteen papers selected by
Kelsey Fisher-Wellman, Wake Forest University

Inner membrane turns inside out to exit mitochondrial organelles.
Lysosomes drive the piecemeal removal of mitochondrial inner membrane.
Misregulation of mitochondrial 6mA promotes the propagation of mutant mtDNA and causes aging in C. elegans.
Cancer tissue of origin constrains the growth and metabolism of metastases.
Mitochondrial uncoupling caused by a wide variety of protonophores is differently sensitive to carboxyatractyloside in rat heart and liver mitochondria.
Malic enzyme 2 maintains metabolic state and anti-tumor immunity of CD8+ T cells.
BRAFV600E/ p-ERK/ p-DRP1(Ser616) Promotes Tumor Progression and Reprogramming of Glucose Metabolism in Papillary Thyroid Cancer.
SLC30A9: an evolutionarily conserved mitochondrial zinc transporter essential for mammalian early embryonic development.
Short-term post-fast refeeding enhances intestinal stemness via polyamines.
FAM210A: An emerging regulator of mitochondrial homeostasis.
Trametinib potentiates anti-PD-1 efficacy in tumors established from chemotherapy-primed pancreatic cancer cells.
The critical role of glutamine and fatty acids in the metabolic reprogramming of anoikis-resistant melanoma cells.
Tretinoin synergistically enhances the antitumor effect of combined BRAF, MEK, and EGFR inhibition in BRAFV600E colorectal cancer.
FDX2, an iron-sulfur cluster assembly factor, is essential to prevent cellular senescence, apoptosis or ferroptosis of ovarian cancer cells.
Structural basis for substrate binding and selection by human mitochondrial RNA polymerase.
Artificial targeting of autophagy components to mitochondria reveals both conventional and unconventional mitophagy pathways.
The role of the primitive marker CD133 in CD34-negative acute myeloid leukemia for the detection of leukemia stem cells.
Adenosine diphosphate released from stressed cells triggers mitochondrial transfer to achieve tissue homeostasis.

Nature. 2024 Aug;632(8027): 987-988

Inner membrane turns inside out to exit mitochondrial organelles.

David Pla-Martín, Andreas S Reichert.



Keywords:  Biochemistry; Cell biology

DOI:  https://doi.org/10.1038/d41586-024-02528-w
Nature. 2024 Aug 21.

Lysosomes drive the piecemeal removal of mitochondrial inner membrane.

Akriti Prashar, Claudio Bussi, Antony Fearns, Mariana I Capurro, Xiaodong Gao, Hiromi Sesaki, Maximiliano G Gutierrez, Nicola L Jones.

Mitochondrial membranes define distinct structural and functional compartments. Cristae of the inner mitochondrial membrane (IMM) function as independent bioenergetic units that undergo rapid and transient remodelling, but the significance of this compartmentalized organization is unknown1. Using super-resolution microscopy, here we show that cytosolic IMM vesicles, devoid of outer mitochondrial membrane or mitochondrial matrix, are formed during resting state. These vesicles derived from the IMM (VDIMs) are formed by IMM herniation through pores formed by voltage-dependent anion channel 1 in the outer mitochondrial membrane. Live-cell imaging showed that lysosomes in proximity to mitochondria engulfed the herniating IMM and, aided by the endosomal sorting complex required for transport machinery, led to the formation of VDIMs in a microautophagy-like process, sparing the remainder of the organelle. VDIM formation was enhanced in mitochondria undergoing oxidative stress, suggesting their potential role in maintenance of mitochondrial function. Furthermore, the formation of VDIMs required calcium release by the reactive oxygen species-activated, lysosomal calcium channel, transient receptor potential mucolipin 1, showing an interorganelle communication pathway for maintenance of mitochondrial homeostasis. Thus, IMM compartmentalization could allow for the selective removal of damaged IMM sections via VDIMs, which should protect mitochondria from localized injury. Our findings show a new pathway of intramitochondrial quality control.

DOI: https://doi.org/10.1038/s41586-024-07835-w
Cell Metab. 2024 Aug 16. pii: S1550-4131(24)00291-2. [Epub ahead of print]

Misregulation of mitochondrial 6mA promotes the propagation of mutant mtDNA and causes aging in C. elegans.

Anne Hahn, Grace Ching Ching Hung, Arnaud Ahier, Chuan-Yang Dai, Ina Kirmes, Brian M Forde, Daniel Campbell, Rachel Shin Yie Lee, Josiah Sucic, Tessa Onraet, Steven Zuryn.

  In virtually all eukaryotes, the mitochondrial DNA (mtDNA) encodes proteins necessary for oxidative phosphorylation (OXPHOS) and RNAs required for their synthesis. The mechanisms of regulation of mtDNA copy number and expression are not completely understood but crucially ensure the correct stoichiometric assembly of OXPHOS complexes from nuclear- and mtDNA-encoded subunits. Here, we detect adenosine N6-methylation (6mA) on the mtDNA of diverse animal and plant species. This modification is regulated in C. elegans by the DNA methyltransferase DAMT-1 and demethylase ALKB-1. Misregulation of mtDNA 6mA through targeted modulation of these activities inappropriately alters mtDNA copy number and transcript levels, impairing OXPHOS function, elevating oxidative stress, and shortening lifespan. Compounding these defects, mtDNA 6mA hypomethylation promotes the cross-generational propagation of a deleterious mtDNA. Together, these results reveal that mtDNA 6mA is highly conserved among eukaryotes and regulates lifespan by influencing mtDNA copy number, expression, and heritable mutation levels in vivo.

Keywords:  6mA; ROS; aging; epigenetics; heteroplasmy; lifespan; mitochondria; mitochondrial genome; mtDNA; oxidative stress

DOI:  https://doi.org/10.1016/j.cmet.2024.07.020
Nat Metab. 2024 Aug 19.

Cancer tissue of origin constrains the growth and metabolism of metastases.

Sharanya Sivanand, Yetis Gultekin, Peter S Winter, Sidney Y Vermeulen, Konstantine M Tchourine, Keene L Abbott, Laura V Danai, Florian Gourgue, Brian T Do, Kayla Crowder, Tenzin Kunchok, Allison N Lau, Alicia M Darnell, Alexandria Jefferson, Satoru Morita, Dan G Duda, Andrew J Aguirre, Brian M Wolpin, Nicole Henning, Virginia Spanoudaki, Laura Maiorino, Darrell J Irvine, Omer H Yilmaz, Caroline A Lewis, Dennis Vitkup, Alex K Shalek, Matthew G Vander Heiden.

Metastases arise from subsets of cancer cells that disseminate from the primary tumour1,2. The ability of cancer cells to thrive in a new tissue site is influenced by genetic and epigenetic changes that are important for disease initiation and progression, but these factors alone do not predict if and where cancers metastasize3,4. Specific cancer types metastasize to consistent subsets of tissues, suggesting that primary tumour-associated factors influence where cancers can grow. We find primary and metastatic pancreatic tumours have metabolic similarities and that the tumour-initiating capacity and proliferation of both primary-derived and metastasis-derived cells is favoured in the primary site relative to the metastatic site. Moreover, propagating cells as tumours in the lung or the liver does not enhance their relative ability to form large tumours in those sites, change their preference to grow in the primary site, nor stably alter aspects of their metabolism relative to primary tumours. Primary liver and lung cancer cells also exhibit a preference to grow in their primary site relative to metastatic sites. These data suggest cancer tissue of origin influences both primary and metastatic tumour metabolism and may impact where cancer cells can metastasize.

DOI: https://doi.org/10.1038/s42255-024-01105-9
Biochim Biophys Acta Bioenerg. 2024 Aug 20. pii: S0005-2728(24)00476-6. [Epub ahead of print]1865(4): 149506

Mitochondrial uncoupling caused by a wide variety of protonophores is differently sensitive to carboxyatractyloside in rat heart and liver mitochondria.

Ljudmila S Khailova, Roman S Kirsanov, Tatyana I Rokitskaya, Vladimir S Krasnov, Galina A Korshunova, Elena A Kotova, Yuri N Antonenko.

  Mitochondrial uncoupling by small-molecule protonophores is generally accepted to proceed via transmembrane proton shuttling. The idea of facilitating this process by the adenine nucleotide translocase ANT originated primarily from the partial reversal of the DNP-induced mitochondrial uncoupling by the ANT inhibitor carboxyatractyloside (CATR). Recently, the sensitivity to CATR was also observed for the action of such potent OxPhos uncouplers as BAM15, SF6847, FCCP and niclosamide. Here, we report measurements of the CATR effect on the activity of a large number of conventional and novel uncouplers in isolated mammalian mitochondria. Despite the broad variety of chemical structures, CATR attenuated the uncoupling efficacy of all the anionic protonophores in rat heart mitochondria with high abundance of ANT, whereas the effect was much less pronounced or even absent, e.g. for SF6847, in rat liver mitochondria with low ANT content. The fact that the uncoupling action is tissue specific for a broad spectrum of anionic protonophores is highlighted here for the first time. Only with the cationic uncoupler ellipticine and the channel-forming peptide gramicidin A, no sensitivity to CATR was found even in rat heart mitochondria. By contrast, with the recently described ester-stabilized ylidic protonophores [Kirsanov et al. Bioelectrochemistry 2023], the stimulating effect of CATR was discovered both in liver and heart mitochondria.

Keywords:  Adenine nucleotide translocator; Carboxyatractyloside; Membrane potential; Mitochondrial uncoupler; Protonophore; Respiration rate

DOI:  https://doi.org/10.1016/j.bbabio.2024.149506
Mol Cell. 2024 Aug 06. pii: S1097-2765(24)00619-1. [Epub ahead of print]

Malic enzyme 2 maintains metabolic state and anti-tumor immunity of CD8+ T cells.

Zhenxi Zhang, Yanting Yang, Yang Chen, Jingyu Su, Wenjing Du.

  The functional integrity of CD8+ T cells is closely linked to metabolic reprogramming; therefore, understanding the metabolic basis of CD8+ T cell activation and antitumor immunity could provide insights into tumor immunotherapy. Here, we report that ME2 is critical for mouse CD8+ T cell activation and immune response against malignancy. ME2 deficiency suppresses CD8+ T cell activation and anti-tumor immune response in vitro and in vivo. Mechanistically, ME2 depletion blocks the TCA cycle flux, leading to the accumulation of fumarate. Fumarate directly binds to DAPK1 and inhibits its activity by competing with ATP for binding. Notably, pharmacological inhibition of DAPK1 abolishes the anti-tumor function conferred by ME2 to CD8+ T cells. Collectively, these findings demonstrate a role for ME2 in the regulation of CD8+ T cell metabolism and effector functions as well as an unexpected function for fumarate as a metabolic signal in the inhibition of DAPK1.

Keywords:  CD8(+) T cell; DAPK1; antitumor immunity; fumarate; malic enzyme 2; metabolite sensing

DOI:  https://doi.org/10.1016/j.molcel.2024.07.021
Thyroid. 2024 Aug 20.

BRAFV600E/ p-ERK/ p-DRP1(Ser616) Promotes Tumor Progression and Reprogramming of Glucose Metabolism in Papillary Thyroid Cancer.

Shishuai Wen, Yijun Wu, Jia-Yang Wang, Zhaoxian Ni, Shuai Dong, Xiaojun Xie, Yu-Ting Wang, Yu Wang, Nai-Si Huang, Qing-Hai Ji, Ben Ma, Ning Qu.

BACKGROUND: Papillary thyroid cancer (PTC) with the BRAFV600E mutation is associated with a poorer prognosis. BRAF inhibitors may demonstrate limited efficacy due to emerging drug resistance. The Warburg effect may have cancer therapeutic implications. It is not known if the BRAFV600E mutation is associated with altered glucose metabolism in PTC.
METHODS: This study examined the effect of the BRAFV600E and DRP1 on various cellular processes in PTC cells, including: cell proliferation, migration, invasion, mitochondrial fission, glucose metabolism, reactive oxygen species (ROS) generation and apoptosis. We used RT-qPCR to assess the expression of key glycolytic enzymes in thyroid cancer tissues. Additionally, the regulatory interaction between BRAFV600E and DRP1 was investigated through Western Blot and immunohistochemical staining. We further evaluated the impact of DRP1 in PTC and inhibitory effects of Dabrafenib and 2-DG in vitro and in vivo.
RESULTS: We found that the BRAFV600E mutation significantly augments aerobic glycolysis while suppressing oxidative phosphorylation in PTC. We identified the BRAFV600E/p-ERK/p-DRP1(Ser616) signaling pathway as a critical mediator in PTC progression. The BRAFV600E/p-ERK/p-DRP1(Ser616) signaling pathway enhances cell proliferation by upregulating HK2 expression and thereby increasing aerobic glycolysis. Secondly, it inhibits apoptosis by promoting mitochondrial fission and reducing ROS levels. Moreover, we demonstrated that the combination therapy of 2-DG and Dabrafenib markedly impedes the progression of BRAFV600E-positive PTC.
CONCLUSION: The BRAFV600E/p-ERK/p-DRP1(Ser616) signaling pathway plays a pivotal role in glucose metabolism reprogramming, contributing to the aggressiveness and progression of BRAFV600E-positive PTC. Our findings suggest that a combined therapeutic approach using 2-DG and Dabrafenib has potential to improve the outcome of PTC patients with BRAFV600E.

DOI: https://doi.org/10.1089/thy.2023.0700
Cell Mol Life Sci. 2024 Aug 19. 81(1): 357

SLC30A9: an evolutionarily conserved mitochondrial zinc transporter essential for mammalian early embryonic development.

Jing Ge, Huihui Li, Xin Liang, Bing Zhou.

  SLC30A9 (ZnT9) is a mitochondria-resident zinc transporter. Mutations in SLC30A9 have been reported in human patients with a novel cerebro-renal syndrome. Here, we show that ZnT9 is an evolutionarily highly conserved protein, with many regions extremely preserved among evolutionarily distant organisms. In Drosophila melanogaster (the fly), ZnT9 (ZnT49B) knockdown results in acutely impaired movement and drastic mitochondrial deformation. Severe Drosophila ZnT9 (dZnT9) reduction and ZnT9-null mutant flies are pupal lethal. The phenotype of dZnT9 knockdown can be partially rescued by mouse ZnT9 expression or zinc chelator TPEN, indicating the defect of dZnT9 loss is indeed a result of zinc dyshomeostasis. Interestingly, in the mouse, germline loss of Znt9 produces even more extreme phenotypes: the mutant embryos exhibit midgestational lethality with severe development abnormalities. Targeted mutagenesis of Znt9 in the mouse brain leads to serious dwarfism and physical incapacitation, followed by death shortly. Strikingly, the GH/IGF-1 signals are almost non-existent in these tissue-specific knockout mice, consistent with the medical finding in some human patients with severe mitochondrial deficiecny. ZnT9 mutations cause mitochondrial zinc dyshomeostasis, and we demonstrate mechanistically that mitochondrial zinc elevation quickly and potently inhibits the activities of respiration complexes. These results reveal the critical role of ZnT9 and mitochondrial zinc homeostasis in mammalian development. Based on our functional analyses, we finally discussed the possible nature of the so far identified human SLC30A9 mutations.

Keywords:  CG8632; Electron transport chain; GH/IGF; ZnT49B; ZnT9

DOI:  https://doi.org/10.1007/s00018-024-05377-y
Nature. 2024 Aug 21.

Short-term post-fast refeeding enhances intestinal stemness via polyamines.

Shinya Imada, Saleh Khawaled, Heaji Shin, Sven W Meckelmann, Charles A Whittaker, Renan Oliveira Corrêa, Chiara Alquati, Yixin Lu, Guodong Tie, Dikshant Pradhan, Gizem Calibasi-Kocal, Luiza Martins Nascentes Melo, Gabriele Allies, Jonas Rösler, Pia Wittenhofer, Jonathan Krystkiewicz, Oliver J Schmitz, Jatin Roper, Marco Aurelio Ramirez Vinolo, Luigi Ricciardiello, Evan C Lien, Matthew G Vander Heiden, Ramesh A Shivdasani, Chia-Wei Cheng, Alpaslan Tasdogan, Ömer H Yilmaz.

For over a century, fasting regimens have improved health, lifespan and tissue regeneration in diverse organisms, including humans1-6. However, how fasting and post-fast refeeding affect adult stem cells and tumour formation has yet to be explored in depth. Here we demonstrate that post-fast refeeding increases intestinal stem cell (ISC) proliferation and tumour formation; post-fast refeeding augments the regenerative capacity of Lgr5+ ISCs, and loss of the tumour suppressor gene Apc in post-fast-refed ISCs leads to a higher tumour incidence in the small intestine and colon than in the fasted or ad libitum-fed states, demonstrating that post-fast refeeding is a distinct state. Mechanistically, we discovered that robust mTORC1 induction in post-fast-refed ISCs increases protein synthesis via polyamine metabolism to drive these changes, as inhibition of mTORC1, polyamine metabolite production or protein synthesis abrogates the regenerative or tumorigenic effects of post-fast refeeding. Given our findings, fast-refeeding cycles must be carefully considered and tested when planning diet-based strategies for regeneration without increasing cancer risk, as post-fast refeeding leads to a burst in stem-cell-driven regeneration and tumorigenicity.

DOI: https://doi.org/10.1038/s41586-024-07840-z
Bioessays. 2024 Aug 19. e2400090

FAM210A: An emerging regulator of mitochondrial homeostasis.

Yubo Wang, Feng Yue.

  Mitochondrial homeostasis serves as a cornerstone of cellular function, orchestrating a delicate balance between energy production, redox status, and cellular signaling transduction. This equilibrium involves a myriad of interconnected processes, including mitochondrial dynamics, quality control mechanisms, and biogenesis and degradation. Perturbations in mitochondrial homeostasis have been implicated in a wide range of diseases, including neurodegenerative diseases, metabolic syndromes, and aging-related disorders. In the past decades, the discovery of numerous mitochondrial proteins and signaling has led to a more complete understanding of the intricate mechanisms underlying mitochondrial homeostasis. Recent studies have revealed that Family with sequence similarity 210 member A (FAM210A) is a novel nuclear-encoded mitochondrial protein involved in multiple aspects of mitochondrial homeostasis, including mitochondrial quality control, dynamics, cristae remodeling, metabolism, and proteostasis. Here, we review the function and physiological role of FAM210A in cellular and organismal health. This review discusses how FAM210A acts as a regulator on mitochondrial inner membrane to coordinate mitochondrial dynamics and metabolism.

Keywords:  FAM210A; cristae remodeling; energy metabolism; mitochondrial dynamics; proteostasis; quality control

DOI:  https://doi.org/10.1002/bies.202400090
Mol Cancer Ther. 2024 Aug 20.

Trametinib potentiates anti-PD-1 efficacy in tumors established from chemotherapy-primed pancreatic cancer cells.

Thao D Pham, Anastasia E Metropulos, Nida Mubin, Jeffrey H Becker, Dhavan Shah, Christina Spaulding, Mario A Shields, David J Bentrem, Hidayatullah G Munshi.

Despite advances in immune checkpoint inhibitors (ICIs), chemotherapy remains the standard therapy for patients with pancreatic ductal adenocarcinoma (PDAC). As the combinations of chemotherapy, including the FOLFIRINOX (5-fluorouracil (5FU), irinotecan, and oxaliplatin) regimen, and ICIs have failed to demonstrate clinical benefit in patients with metastatic PDAC tumors, there is increasing interest in identifying therapeutic approaches to potentiate ICI efficacy in PDAC patients. In this study, we report that neoadjuvant FOLFRINOX-treated human PDAC tumors exhibit increased MEK/ERK activation. We also show elevated MEK/ERK signaling in ex vivo PDAC slice cultures and cell lines treated with a combination of 5FU (F), irinotecan (I), and oxaliplatin (O) (FIO). In addition, we find that the KPC-FIO cells, established from repeated treatment of mouse PDAC cell lines with 6-8 cycles of FIO, display enhanced ERK phosphorylation and demonstrate increased sensitivity to MEK inhibition in vitro and in vivo. Significantly, the KPC-FIO cells develop tumors with a pro-inflammatory immune profile similar to human PDAC tumors following neoadjuvant FOLFIRINOX treatment. Furthermore, we found that the MEK inhibitor Trametinib enables additional infiltration of highly functional CD8+ T cells into the KPC-FIO tumors and potentiates the efficacy of anti-PD-1 antibody in syngeneic mouse models. Our findings provide a rationale for combining Trametinib and anti-PD-1 antibodies in PDAC patients following neoadjuvant or short-term FOLFIRINOX treatment to achieve effective anti-tumor responses.

DOI: https://doi.org/10.1158/1535-7163.MCT-23-0833
Front Pharmacol. 2024 ;15 1422281

The critical role of glutamine and fatty acids in the metabolic reprogramming of anoikis-resistant melanoma cells.

S Peppicelli, T Kersikla, G Menegazzi, E Andreucci, J Ruzzolini, C Nediani, F Bianchini, L Calorini.

  Introduction: Circulating tumor cells (CTCs) represent the sub-population of cells shed into the vasculature and able to survive in the bloodstream, adhere to target vascular endothelial cells, and re-growth into the distant organ. CTCs have been found in the blood of most solid tumor-bearing patients and are used as a diagnostic marker. Although a complex genotypic and phenotypic signature characterizes CTCs, the ability to survive in suspension constitutes the most critical property, known as resistance to anoikis, e.g., the ability to resist apoptosis resulting from a loss of substrate adhesion. Here, we selected melanoma cells resistant to anoikis, and we studied their metabolic reprogramming, with the aim of identifying new metabolic targets of CTCs. Methods: Subpopulations of melanoma cells expressing a high anoikis-resistant phenotype were selected by three consecutive rocking exposures in suspension and studied for their phenotypic and metabolic characteristics. Moreover, we tested the efficacy of different metabolic inhibitors targeting glycolysis (2DG), LDHA (LDHA-in-3), the mitochondrial electron transport chain complex I (rotenone), glutaminase (BPTES), fatty acid transporter (SSO), fatty acid synthase (denifanstat), CPT1 (etomoxir), to inhibit cell survival and colony formation ability after 24 h of rocking condition. Results: Anoikis-resistant cells displayed higher ability to grow in suspension on agarose-covered dishes respect to control cells, and higher cell viability and colony formation capability after a further step in rocking condition. They showed also an epithelial-to-mesenchymal transition associated with high invasiveness and a stemness-like phenotype. Anoikis-resistant melanoma cells in suspension showed a metabolic reprogramming from a characteristic glycolytic metabolism toward a more oxidative metabolism based on the use of glutamine and fatty acids, while re-adhesion on the dishes reversed the metabolism to glycolysis. The treatment with metabolic inhibitors highlighted the effectiveness of rotenone, BPTES, SSO, and etomoxir in reducing the viability and the colony formation ability of cells capable of surviving in suspension, confirming the dependence of their metabolism on oxidative phosphorylation, using glutamine and fatty acids as the most important fuels. Discussion: This finding opens up new therapeutic strategies based on metabolic inhibitors of glutaminase and fatty acid oxidation for the treatment of CTCs and melanoma metastases.

Keywords:  anoikis resistance; cell metabolism; circulating tumor cells; melanoma; therapy

DOI:  https://doi.org/10.3389/fphar.2024.1422281
Cancer Sci. 2024 Aug 22.

Tretinoin synergistically enhances the antitumor effect of combined BRAF, MEK, and EGFR inhibition in BRAFV600E colorectal cancer.

Yuya Yoshida, Masanobu Takahashi, Sakura Taniguchi, Ryunosuke Numakura, Keigo Komine, Chikashi Ishioka.

  Patients with BRAF-mutated colorectal cancer (BRAFV600E CRC) are currently treated with a combination of BRAF inhibitor and anti-EGFR antibody with or without MEK inhibitor. A fundamental problem in treating patients with BRAFV600E CRC is intrinsic and/or acquired resistance to this combination therapy. By screening 78 compounds, we identified tretinoin, a retinoid, as a compound that synergistically enhances the antiproliferative effect of a combination of BRAF inhibition and MEK inhibition with or without EGFR inhibition on BRAFV600E CRC cells. This synergistic effect was also exerted by other retinoids. Tretinoin, added to BRAF inhibitor and MEK inhibitor, upregulated PARP, BAK, and p-H2AX. When either RARα or RXRα was silenced, the increase in cleaved PARP expression by the addition of TRE to ENC/BIN or ENC/BIN/CET was canceled. Our results suggest that the mechanism of the synergistic antiproliferative effect involves modulation of the Bcl-2 family and the DNA damage response that affects apoptotic pathways, and this synergistic effect is induced by RARα- or RXRα-mediated apoptosis. Tretinoin also enhanced the antitumor effect of a combination of the BRAF inhibitor and anti-EGFR antibody with or without MEK inhibitor in a BRAFV600E CRC xenograft mouse model. Our data provide a rationale for developing retinoids as a new combination agent to overcome resistance to the combination therapy for patients with BRAFV600E CRC.

Keywords:  BRAF inhibitor; MEK inhibitor; colorectal cancer; retinoid; tretinoin

DOI:  https://doi.org/10.1111/cas.16280
J Biol Chem. 2024 Aug 14. pii: S0021-9258(24)02179-3. [Epub ahead of print] 107678

FDX2, an iron-sulfur cluster assembly factor, is essential to prevent cellular senescence, apoptosis or ferroptosis of ovarian cancer cells.

Shuko Miyahara, Mai Ohuchi, Miyuki Nomura, Eifumi Hashimoto, Tomoyoshi Soga, Rintaro Saito, Kayoko Hayashi, Taku Sato, Masatoshi Saito, Yoji Yamashita, Muneaki Shimada, Nobuo Yaegashi, Hidekazu Yamada, Nobuhiro Tanuma.

  Recent studies reveal that biosynthesis of iron-sulfur clusters (Fe-Ss) is essential for cell proliferation, including that of cancer cells. Nonetheless, it remains unclear how Fe-S biosynthesis functions in cell proliferation/survival. Here, we report that proper Fe-S biosynthesis is essential to prevent cellular senescence, apoptosis or ferroptosis, depending on cell context. To assess these outcomes in cancer, we developed an ovarian cancer line with conditional KO of FDX2, a component of the core Fe-S assembly complex. FDX2 loss induced global down-regulation of Fe-S-containing proteins and Fe2+ overload, resulting in DNA damage and p53 pathway activation, and driving the senescence program. p53-deficiency augmented DNA damage responses upon FDX2 loss, resulting in apoptosis rather than senescence. FDX2 loss also sensitized cells to ferroptosis, as evidenced by compromised redox homeostasis of membrane phospholipids (PLs). Our results suggest that p53 status and PL homeostatic activity are critical determinants of diverse biological outcomes of Fe-S deficiency in cancer cells.

Keywords:  DNA damage response; cancer biology; cell death; cellular senescence; gene knockout; iron metabolism; iron-sulfur protein; ovarian cancer; p53; reactive oxygen species (ROS); redox regulation; tumor metabolism

DOI:  https://doi.org/10.1016/j.jbc.2024.107678
Nat Commun. 2024 Aug 20. 15(1): 7134

Structural basis for substrate binding and selection by human mitochondrial RNA polymerase.

Karl Herbine, Ashok R Nayak, Dmitry Temiakov.

The mechanism by which RNAP selects cognate substrates and discriminates between deoxy and ribonucleotides is of fundamental importance to the fidelity of transcription. Here, we present cryo-EM structures of human mitochondrial transcription elongation complexes that reveal substrate ATP bound in Entry and Insertion Sites. In the Entry Site, the substrate binds along the O helix of the fingers domain of mtRNAP but does not interact with the templating DNA base. Interactions between RNAP and the triphosphate moiety of the NTP in the Entry Site ensure discrimination against nucleosides and their diphosphate and monophosphate derivatives but not against non-cognate rNTPs and dNTPs. Closing of the fingers domain over the catalytic site results in delivery of both the templating DNA base and the substrate into the Insertion Site and recruitment of the catalytic magnesium ions. The cryo-EM data also reveal a conformation adopted by mtRNAP to reject a non-cognate substrate from its active site. Our findings establish a structural basis for substrate binding and suggest a unified mechanism of NTP selection for single-subunit RNAPs.

DOI: https://doi.org/10.1038/s41467-024-50817-9
Autophagy. 2024 Aug 23.

Artificial targeting of autophagy components to mitochondria reveals both conventional and unconventional mitophagy pathways.

Katharina C Lorentzen, Alan R Prescott, Ian G Ganley.

  Macroautophagy/autophagy enables lysosomal degradation of a diverse array of intracellular material. This process is essential for normal cellular function and its dysregulation is implicated in many diseases. Given this, there is much interest in understanding autophagic mechanisms of action in order to determine how it can be best targeted therapeutically. In mitophagy, the selective degradation of mitochondria via autophagy, mitochondria first need to be primed with signals that allow the recruitment of the core autophagy machinery to drive the local formation of an autophagosome around the target mitochondrion. To determine how the recruitment of different core autophagy components can drive mitophagy, we took advantage of the mito-QC mitophagy assay (an outer mitochondrial membrane-localized tandem mCherry-GFP tag). By tagging autophagy proteins with an anti-mCherry (or anti-GFP) nanobody, we could recruit them to mitochondria and simultaneously monitor levels of mitophagy. We found that targeting ULK1, ATG16L1 and the different Atg8-family proteins was sufficient to induce mitophagy. Mitochondrial recruitment of ULK1 and the Atg8-family proteins induced a conventional mitophagy pathway, requiring RB1CC1/FIP200, PIK3C3/VPS34 activity and ATG5. Surprisingly, the mitophagy pathway upon recruitment of ATG16L1 proceeded independently of ATG5, although it still required RB1CC1 and PIK3C3/VPS34 activity. In this latter pathway, mitochondria were alternatively delivered to lysosomes via uptake into early endosomes.

Keywords:  ATG16L1; Atg8; ULK1; nanobody; targeted organelle degradation

DOI:  https://doi.org/10.1080/15548627.2024.2395149
Cytometry B Clin Cytom. 2024 Aug 23.

The role of the primitive marker CD133 in CD34-negative acute myeloid leukemia for the detection of leukemia stem cells.

Tom Reuvekamp, Luca L G Janssen, Lok Lam Ngai, Jannemieke Carbaat-Ham, Daphne den Hartog, Willemijn J Scholten, Angèle Kelder, Diana Hanekamp, Eliza Wensink, Noortje van Gils, Patrycja Gradowska, Bob Löwenberg, Gert J Ossenkoppele, Arjan A van de Loosdrecht, Theresia M Westers, Linda Smit, Costa Bachas, Jacqueline Cloos.

  The most important reason for dismal outcomes in acute myeloid leukemia (AML) is the development of relapse. Leukemia stem cells (LSCs) are hypothesized to initiate relapse, and high CD34+CD38- LSC load is associated with poor prognosis. In 10% of AML patients, CD34 is not or is low expressed on the leukemic cells (<1%), and CD34+CD38- LSCs are absent. These patients are classified as CD34-negative. We aimed to determine whether the primitive marker CD133 can detect LSCs in CD34-negative AML. We retrospectively quantified 148 CD34-negative patients for proportions of CD34-CD133+ and CD133+CD38- cell fractions in the diagnostic samples of CD34-negative patients in the HOVON102 and HOVON132 trials. No prognostic difference was found between patients with high or low proportions of CD34-CD133+, which is found to be aberrantly expressed in AML. A high level of CD133+CD38- cells was not associated with poor overall survival, and expression in AML was similar to normal bone marrow. To conclude, CD133 is useful as an additional primitive marker for the detection of leukemic blast cells in CD34-negative AML. However, CD133+CD38 alone is not suitable for the detection of LSCs at diagnosis.

Keywords:  CD133; acute myeloid leukemia; flow cytometry; leukemia stem cells; measurable residual disease

DOI:  https://doi.org/10.1002/cyto.b.22201
PLoS Biol. 2024 Aug;22(8): e3002753

Adenosine diphosphate released from stressed cells triggers mitochondrial transfer to achieve tissue homeostasis.

Hao Li, Hongping Yu, Delin Liu, Peng Liao, Chuan Gao, Jian Zhou, Jialun Mei, Yao Zong, Peng Ding, Meng Yao, Bingqi Wang, Yafei Lu, Yigang Huang, Youshui Gao, Changqing Zhang, Minghao Zheng, Junjie Gao.

Cell-to-cell mitochondrial transfer has recently been shown to play a role in maintaining physiological functions of cell. We previously illustrated that mitochondrial transfer within osteocyte dendritic network regulates bone tissue homeostasis. However, the mechanism of triggering this process has not been explored. Here, we showed that stressed osteocytes in mice release adenosine diphosphate (ADP), resulting in triggering mitochondrial transfer from healthy osteocytes to restore the oxygen consumption rate (OCR) and to alleviate reactive oxygen species accumulation. Furthermore, we identified that P2Y2 and P2Y6 transduced the ADP signal to regulate osteocyte mitochondrial transfer. We showed that mitochondrial metabolism is impaired in aged osteocytes, and there were more extracellular nucleotides release into the matrix in aged cortical bone due to compromised membrane integrity. Conditioned medium from aged osteocytes triggered mitochondrial transfer between osteocytes to enhance the energy metabolism. Together, using osteocyte as an example, this study showed new insights into how extracellular ADP triggers healthy cells to rescue energy metabolism crisis in stressed cells via mitochondrial transfer in tissue homeostasis.

DOI: https://doi.org/10.1371/journal.pbio.3002753