bims-lymeca Biomed News
on Lysosome metabolism in cancer
Issue of 2022–02–13
nineteen papers selected by
Harilaos Filippakis, Harvard University
  1. Disrupting the MYC-TFEB Circuit Impairs Amino Acid Homeostasis and Provokes Metabolic Anergy.
  2. Built to last: lysosome remodeling and repair in health and disease.
  3. Activation of endo-lysosomal two-pore channels by NAADP and PI(3,5)P2. Five things to know.
  4. The hallmarks of cancer metabolism: Still emerging.
  5. Tri-2-Hydroxyarachidonein Induces Cytocidal Autophagy in Pancreatic Ductal Adenocarcinoma Cancer Cell Models.
  6. A mechanistic modeling framework reveals the key principles underlying tumor metabolism.
  7. Development of a novel spatiotemporal depletion system for cellular cholesterol.
  8. Personalized Medicine for Prostate Cancer: Is Targeting Metabolism a Reality?
  9. Cryo-EM of the Yeast VO Complex Reveals Distinct Binding Sites for Macrolide V-ATPase Inhibitors.
  10. Combined inhibition of G9a and EZH2 suppresses tumor growth via synergistic induction of IL24-mediated apoptosis.
  11. Escape From Cisplatin-Induced Senescence of Hypoxic Lung Cancer Cells Can Be Overcome by Hydroxychloroquine.
  12. Research Progress and Prospects of Autophagy in the Mechanism of Multidrug Resistance in Tumors.
  13. Involvement of calcium signaling in different types of cell death in cancer.
  14. Small Molecule MMRi62 Induces Ferroptosis and Inhibits Metastasis in Pancreatic Cancer via Degradation of Ferritin Heavy Chain and Mutant p53.
  15. The transcriptional elongation factor CTR9 demarcates PRC2-mediated H3K27me3 domains by altering PRC2 subtype equilibrium.
  16. PD-L1 promotes myofibroblastic activation of hepatic stellate cells by distinct mechanisms selective for TGF-β receptor I versus II.
  17. Low-Density Lipoprotein Internalization, Degradation and Receptor Recycling Along Membrane Contact Sites.
  18. Liquid-liquid phase separation drives cellular function and dysfunction in cancer.
  19. Structural mechanism of allosteric activation of TRPML1 by PI(3,5)P2 and rapamycin.
  1. Cancer Res. 2022 Feb 11. pii: canres.1168.2021. [Epub ahead of print]
    Disrupting the MYC-TFEB Circuit Impairs Amino Acid Homeostasis and Provokes Metabolic Anergy.
    Mario R Fernandez, Franz X Schaub, Chunying Yang, Weimin Li, Seongseok Yun, Stephanie K Schaub, Frank C Dorsey, Min Liu, Meredith A Steeves, Andrea Ballabio, Alexandar Tzankov, Zhihua Chen, John M Koomen, Anders E Berglund, John L Cleveland.
      MYC family oncoproteins are regulators of metabolic reprogramming that sustains cancer cell anabolism. Normal cells adapt to nutrient-limiting conditions by activating autophagy, which is required for amino acid (AA) homeostasis. Here we report that the autophagy pathway is suppressed by Myc in normal B cells, in premalignant and neoplastic B cells of Eμ-Myc transgenic mice, and in human MYC-driven Burkitt lymphoma. Myc suppresses autophagy by antagonizing the expression and function of transcription factor EB (TFEB), a master regulator of autophagy. Mechanisms that sustained AA pools in MYC-expressing B cells include coordinated induction of the proteasome and increases in AA transport. Reactivation of the autophagy-lysosomal pathway by TFEB disabled the malignant state by disrupting mitochondrial functions, proteasome activity, amino acid transport, and amino acid and nucleotide metabolism, leading to metabolic anergy, growth arrest and apoptosis. This phenotype provides therapeutic opportunities to disable MYC-driven malignancies, including AA restriction and treatment with proteasome inhibitors.
    DOI:  https://doi.org/10.1158/0008-5472.CAN-21-1168
  2. Trends Cell Biol. 2022 Feb 02. pii: S0962-8924(22)00001-0. [Epub ahead of print]
    Built to last: lysosome remodeling and repair in health and disease.
    Roberto Zoncu, Rushika M Perera.
      Lysosomes play major roles in growth regulation and catabolism and are recognized as critical mediators of cellular remodeling. An emerging theme is how the lysosome is itself subjected to extensive remodeling in order to perform specific tasks that meet the changing demands of the cell. Accordingly, lysosomes can sustain physical damage and undergo dramatic changes in composition following pathogen infection, accumulation of protein aggregates, or cellular transformation, necessitating dedicated pathways for their repair, remodeling, and restoration. In this review, we focus on emerging molecular mechanisms for piecemeal remodeling of lysosomal components and wholesale repair and discuss their implications in physiological and pathogenic challenges such as cancer, neurodegeneration, and pathogen infection.
    Keywords:  cancer; infection; lysosome; membrane damage; neurodegeneration; repair
    DOI:  https://doi.org/10.1016/j.tcb.2021.12.009
  3. Cell Calcium. 2022 Jan 25. pii: S0143-4160(22)00018-5. [Epub ahead of print]103 102543
    Activation of endo-lysosomal two-pore channels by NAADP and PI(3,5)P2. Five things to know.
    Sandip Patel, Yu Yuan, Gihan S Gunaratne, Taufiq Rahman, Jonathan S Marchant.
      Two-pore channels are ancient members of the voltage-gated ion channel superfamily that are expressed predominantly on acidic organelles such as endosomes and lysosomes. Here we review recent advances in understanding how TPCs are activated by their ligands and identify five salient features: (1) TPCs are Ca2+-permeable non-selective cation channels gated by NAADP. (2) NAADP activation is indirect through associated NAADP receptors. (3) TPCs are also Na+-selective channels gated by PI(3,5)P2. (4) PI(3,5)P2 activation is direct through a structurally-resolved binding site. (5) TPCs switch their ion selectivity in an agonist-dependent manner.
    Keywords:  Ca2+; Endosomes; JPT2; LSM12; Lysosomes; TPC1; TPC2:TPC3; TPCN1; TPCN2; TPCN3
    DOI:  https://doi.org/10.1016/j.ceca.2022.102543
  4. Cell Metab. 2022 Feb 01. pii: S1550-4131(22)00022-5. [Epub ahead of print]
    The hallmarks of cancer metabolism: Still emerging.
    Natalya N Pavlova, Jiajun Zhu, Craig B Thompson.
      Metabolism of cancer cells is geared toward biomass production and proliferation. Since the metabolic resources within the local tissue are finite, this can lead to nutrient depletion and accumulation of metabolic waste. To maintain growth in these conditions, cancer cells employ a variety of metabolic adaptations, the nature of which is collectively determined by the physiology of their cell of origin, the identity of transforming lesions, and the tissue in which cancer cells reside. Furthermore, select metabolites not only serve as substrates for energy and biomass generation, but can also regulate gene and protein expression and influence the behavior of non-transformed cells in the tumor vicinity. As they grow and metastasize, tumors can also affect and be affected by the nutrient distribution within the body. In this hallmark update, recent advances are incorporated into a conceptual framework that may help guide further research efforts in exploring cancer cell metabolism.
    DOI:  https://doi.org/10.1016/j.cmet.2022.01.007
  5. Front Physiol. 2021 ;12 782525
    Tri-2-Hydroxyarachidonein Induces Cytocidal Autophagy in Pancreatic Ductal Adenocarcinoma Cancer Cell Models.
    Javier Fernández-Díaz, Roberto Beteta-Göbel, Manuel Torres, Joan Cabot, Paula Fernández-García, Victoria Lladó, Pablo V Escribá, Xavier Busquets.
      Cell proliferation in pancreatic cancer is determined by a complex network of signaling pathways. Despite the extensive understanding of these protein-mediated signaling processes, there are no significant drug discoveries that could considerably improve a patient's survival. However, the recent understanding of lipid-mediated signaling gives a new perspective on the control of the physiological state of pancreatic cells. Lipid signaling plays a major role in the induction of cytocidal autophagy and can be exploited using synthetic lipids to induce cell death in pancreatic cancer cells. In this work, we studied the activity of a synthetic lipid, tri-2-hydroxyarachidonein (TGM4), which is a triacylglycerol mimetic that contains three acyl moieties with four double bonds each, on cellular and in vivo models of pancreatic cancer. We demonstrated that TGM4 inhibited proliferation of Mia-PaCa-2 (human pancreatic carcinoma) and PANC-1 (human pancreatic carcinoma of ductal cells) in in vitro models and in an in vivo xenograft model of Mia-PaCa-2 cells. In vitro studies demonstrated that TGM4 induced cell growth inhibition paralleled with an increased expression of PARP and CHOP proteins together with the presence of sub-G0 cell cycle events, indicating cell death. This cytocidal effect was associated with elevated ER stress or autophagy markers such as BIP, LC3B, and DHFR. In addition, TGM4 activated peroxisome proliferator-activated receptor gamma (PPAR-γ), which induced elevated levels of p-AKT and downregulation of p-c-Jun. We conclude that TGM4 induced pancreatic cell death by activation of cytocidal autophagy. This work highlights the importance of lipid signaling in cancer and the use of synthetic lipid structures as novel and potential approaches to treat pancreatic cancer and other neoplasias.
    Keywords:  autophagy; cancer; cell death; oncology; pancreas; signal transduction; synthetic lipid
    DOI:  https://doi.org/10.3389/fphys.2021.782525
  6. PLoS Comput Biol. 2022 Feb 11. 18(2): e1009841
    A mechanistic modeling framework reveals the key principles underlying tumor metabolism.
    Shubham Tripathi, Jun Hyoung Park, Shivanand Pudakalakatti, Pratip K Bhattacharya, Benny Abraham Kaipparettu, Herbert Levine.
      While aerobic glycolysis, or the Warburg effect, has for a long time been considered a hallmark of tumor metabolism, recent studies have revealed a far more complex picture. Tumor cells exhibit widespread metabolic heterogeneity, not only in their presentation of the Warburg effect but also in the nutrients and the metabolic pathways they are dependent on. Moreover, tumor cells can switch between different metabolic phenotypes in response to environmental cues and therapeutic interventions. A framework to analyze the observed metabolic heterogeneity and plasticity is, however, lacking. Using a mechanistic model that includes the key metabolic pathways active in tumor cells, we show that the inhibition of phosphofructokinase by excess ATP in the cytoplasm can drive a preference for aerobic glycolysis in fast-proliferating tumor cells. The differing rates of ATP utilization by tumor cells can therefore drive heterogeneity with respect to the presentation of the Warburg effect. Building upon this idea, we couple the metabolic phenotype of tumor cells to their migratory phenotype, and show that our model predictions are in agreement with previous experiments. Next, we report that the reliance of proliferating cells on different anaplerotic pathways depends on the relative availability of glucose and glutamine, and can further drive metabolic heterogeneity. Finally, using treatment of melanoma cells with a BRAF inhibitor as an example, we show that our model can be used to predict the metabolic and gene expression changes in cancer cells in response to drug treatment. By making predictions that are far more generalizable and interpretable as compared to previous tumor metabolism modeling approaches, our framework identifies key principles that govern tumor cell metabolism, and the reported heterogeneity and plasticity. These principles could be key to targeting the metabolic vulnerabilities of cancer.
    DOI:  https://doi.org/10.1371/journal.pcbi.1009841
  7. J Lipid Res. 2022 Feb 07. pii: S0022-2275(22)00011-6. [Epub ahead of print] 100178
    Development of a novel spatiotemporal depletion system for cellular cholesterol.
    Ha Pham, Indira Singaram, Jiachen Sun, Arthur Ralko, Madalyn Puckett, Ashutosh Sharma, Alice Vrielink, Wonhwa Cho.
      Cholesterol is an essential component of mammalian cell membranes whose subcellular concentration and function are tightly regulated by de novo biosynthesis, transport, and storage. Although recent reports have suggested diverse functions of cellular cholesterol in different subcellular membranes, systematic investigation of its site-specific roles has been hampered by the lack of a methodology for spatiotemporal manipulation of cellular cholesterol levels. Here we report development of a new cholesterol depletion system that allows for spatiotemporal manipulation of intracellular cholesterol levels. This system utilizes a genetically-encoded cholesterol oxidase whose intrinsic membrane binding activity is engineered in such a way that its membrane targeting can be controlled in a spatiotemporally specific manner via chemically-induced dimerization. In combination with in situ quantitative imaging of cholesterol and signaling activity measurements, this system allows for unambiguous determination of site-specific functions of cholesterol in different membranes, including the plasma membrane and the lysosomal membrane.
    Keywords:  Chemically induced dimerization; Cholesterol; Cholesterol quantification; Cholesterol signaling; Lysosomes; Plasma membrane; Site-specific depletion
    DOI:  https://doi.org/10.1016/j.jlr.2022.100178
  8. Front Oncol. 2021 ;11 778761
    Personalized Medicine for Prostate Cancer: Is Targeting Metabolism a Reality?
    Gio Fidelito, Matthew J Watt, Renea A Taylor.
      Prostate cancer invokes major shifts in gene transcription and metabolic signaling to mediate alterations in nutrient acquisition and metabolic substrate selection when compared to normal tissues. Exploiting such metabolic reprogramming is proposed to enable the development of targeted therapies for prostate cancer, yet there are several challenges to overcome before this becomes a reality. Herein, we outline the role of several nutrients known to contribute to prostate tumorigenesis, including fatty acids, glucose, lactate and glutamine, and discuss the major factors contributing to variability in prostate cancer metabolism, including cellular heterogeneity, genetic drivers and mutations, as well as complexity in the tumor microenvironment. The review draws from original studies employing immortalized prostate cancer cells, as well as more complex experimental models, including animals and humans, that more accurately reflect the complexity of the in vivo tumor microenvironment. In synthesizing this information, we consider the feasibility and potential limitations of implementing metabolic therapies for prostate cancer management.
    Keywords:  lipid metabolism; metabolic heterogeneity; metabolic targeting; metabolism; obesity; patient-derived xenograft; prostate neoplasia
    DOI:  https://doi.org/10.3389/fonc.2021.778761
  9. ACS Chem Biol. 2022 Feb 11.
    Cryo-EM of the Yeast VO Complex Reveals Distinct Binding Sites for Macrolide V-ATPase Inhibitors.
    Kristine A Keon, Samir Benlekbir, Susanne H Kirsch, Rolf Müller, John L Rubinstein.
      Vacuolar-type adenosine triphosphatases (V-ATPases) are proton pumps found in almost all eukaryotic cells. These enzymes consist of a soluble catalytic V1 region that hydrolyzes ATP and a membrane-embedded VO region responsible for proton translocation. V-ATPase activity leads to acidification of endosomes, phagosomes, lysosomes, secretory vesicles, and the trans-Golgi network, with extracellular acidification occurring in some specialized cells. Small-molecule inhibitors of V-ATPase have played a crucial role in elucidating numerous aspects of cell biology by blocking acidification of intracellular compartments, while therapeutic use of V-ATPase inhibitors has been proposed for the treatment of cancer, osteoporosis, and some infections. Here, we determine structures of the isolated VO complex from Saccharomyces cerevisiae bound to two well-known macrolide inhibitors: bafilomycin A1 and archazolid A. The structures reveal different binding sites for the inhibitors on the surface of the proton-carrying c ring, with only a small amount of overlap between the two sites. Binding of both inhibitors is mediated primarily through van der Waals interactions in shallow pockets and suggests that the inhibitors block rotation of the ring. Together, these structures indicate the existence of a large chemical space available for V-ATPase inhibitors that block acidification by binding the c ring.
    DOI:  https://doi.org/10.1021/acschembio.1c00894
  10. Cancer Res. 2022 Feb 11. pii: canres.2218.2021. [Epub ahead of print]
    Combined inhibition of G9a and EZH2 suppresses tumor growth via synergistic induction of IL24-mediated apoptosis.
    Francesco Casciello, Gregory M Kelly, Priya Ramarao-Milne, Nabilah Kamal, Teneale A Stewart, Pamela Mukhopadhyay, Stephen H Kazakoff, Mariska Miranda, Dorim Kim, Felicity M Davis, Nicholas K Hayward, Paula M Vertino, Nicola Waddell, Frank Gannon, Jason S Lee.
      G9a and EZH2 are two histone methyltransferases commonly upregulated in several cancer types, yet the precise roles that these enzymes play cooperatively in cancer is unclear. We demonstrate here that frequent concurrent upregulation of both G9a and EZH2 occurs in several human tumors. These methyltransferases cooperatively repressed molecular pathways responsible for tumor cell death. In genetically distinct tumor subtypes, concomitant inhibition of G9a and EZH2 potently induced tumor cell death, highlighting the existence of tumor cell survival dependency at the epigenetic level. G9a and EZH2 synergistically repressed expression of genes involved in the induction of endoplasmic reticulum (ER) stress and the production of reactive oxygen species. IL24 was essential for the induction of tumor cell death and was identified as a common target of G9a and EZH2. Loss-of-function of G9a and EZH2 activated the IL24-ER stress axis and increased apoptosis in cancer cells while not affecting normal cells. These results indicate that G9a and EZH2 promotes the evasion of ER stress-mediated apoptosis by repressing IL24 transcription, therefore suggesting that their inhibition may represent a potential therapeutic strategy for solid cancers.
    DOI:  https://doi.org/10.1158/0008-5472.CAN-21-2218
  11. Front Oncol. 2021 ;11 738385
    Escape From Cisplatin-Induced Senescence of Hypoxic Lung Cancer Cells Can Be Overcome by Hydroxychloroquine.
    Aleksandra Olszewska, Agata Borkowska, Monika Granica, Justyna Karolczak, Bartosz Zglinicki, Claudine Kieda, Halina Was.
      Chemotherapy is the commonly used treatment for advanced lung cancer. However, it produces side effects such as the development of chemoresistance. A possible responsible mechanism may be therapy-induced senescence (TIS). TIS cells display increased senescence-associated β-galactosidase (SA-β-gal) activity and irreversible growth arrest. However, recent data suggest that TIS cells can reactivate their proliferative potential and lead to cancer recurrence. Our previous study indicated that reactivation of proliferation by TIS cells might be related with autophagy modulation. However, exact relationship between both processes required further studies. Therefore, the aim of our study was to investigate the role of autophagy in the senescence-related chemoresistance of lung cancer cells. For this purpose, human and murine lung cancer cells were treated with two commonly used chemotherapeutics: cisplatin (CIS), which forms DNA adducts or docetaxel (DOC), a microtubule poison. Hypoxia, often overlooked in experimental settings, has been implicated as a mechanism responsible for a significant change in the response to treatment. Thus, cells were cultured under normoxic (~19% O2) or hypoxic (1% O2) conditions. Herein, we show that hypoxia increases resistance to CIS. Lung cancer cells cultured under hypoxic conditions escaped from CIS-induced senescence, displayed reduced SA-β-gal activity and a decreased percentage of cells in the G2/M phase of the cell cycle. In turn, hypoxia increased the proliferation of lung cancer cells and the proportion of cells proceeding to the G0/G1 phase. Further molecular analyses demonstrated that hypoxia inhibited the prosenescent p53/p21 signaling pathway and induced epithelial to mesenchymal transition in CIS-treated cancer cells. In cells treated with DOC, such effects were not observed. Of importance, pharmacological autophagy inhibitor, hydroxychloroquine (HCQ) was capable of overcoming short-term CIS-induced resistance of lung cancer cells in hypoxic conditions. Altogether, our data demonstrated that hypoxia favors cancer cell escape from CIS-induced senescence, what could be overcome by inhibition of autophagy with HCQ. Therefore, we propose that HCQ might be used to interfere with the ability of senescent cancer cells to repopulate following exposure to DNA-damaging agents. This effect, however, needs to be tested in a long-term perspective for preclinical and clinical applications.
    Keywords:  autophagy; cancer; chemoresistance; hypoxia; senescence
    DOI:  https://doi.org/10.3389/fonc.2021.738385
  12. J Oncol. 2022 ;2022 7032614
    Research Progress and Prospects of Autophagy in the Mechanism of Multidrug Resistance in Tumors.
    Wenqing Long, Lijun Zhang, Yuxing Wang, Haijuan Xie, Lin Wang, Hongnu Yu.
      Although the treatment of cancer has made great strides in clinical practice, its high morbidity and fatality rates remain a major threat to human health. Multidrug resistance (MDR) often appears in the process of tumor treatment, leading to tumor refractory and aggravating the risk of tumor recurrence. Therefore, antitumor MDR plays a key role in tumor chemotherapy. Autophagy is an important process for the turnover of intracellular materials, which is commonly seen in the treatment of sensitive and multidrug-resistant tumors, and it can play different roles in various types of MDR tumor cells and tissues. Autophagy plays a dual regulatory role in MDR tumors. On the one hand, autophagy can promote the formation of MDR in tumor cells, weaken the killing effect of chemotherapy drugs on tumor cells, and play a protective role in tumor survival. On the other hand, autophagy production in the cellular environment can kill MDR tumor cells, reverse tumor resistance and enhance the efficiency of chemotherapy drugs. Therefore, the regulation of autophagy to overcome MDR has become increasingly significant in tumor chemotherapy. In this article, we discussed and summarized the research progress of autophagy in MDR tumors, mainly involving the different characteristics of autophagy in MDR cancer cells.
    DOI:  https://doi.org/10.1155/2022/7032614
  13. Neoplasma. 2022 Feb 10. pii: 220127N121. [Epub ahead of print]
    Involvement of calcium signaling in different types of cell death in cancer.
    Petr Babula, Olga Krizanova.
      Programmed cell death is a basic feature of chemotherapeutic (and also radiotherapeutic) intervention. Induction of cell death in tumor cells aims to kill preferentially the tumor cells, with minimal impact on the normal cells. Although apoptosis is the most obvious type of cell death induced by chemotherapeutics, several other types can also be activated, especially in conditions, where cells are resistant to apoptosis induction. Calcium signaling was shown to play an indisputable role in the activation of different types of cell death. Local increase of the calcium in time and precise place of this increase is secured by calcium transport systems. In this review, we summarized the involvement of some calcium transport systems in apoptosis, autophagy, necroptosis, ferroptosis, and mitophagy during cancer development and treatment.
    DOI:  https://doi.org/10.4149/neo_2022_220127N121
  14. Mol Cancer Ther. 2022 Feb 07. pii: molcanther.0728.2021. [Epub ahead of print]
    Small Molecule MMRi62 Induces Ferroptosis and Inhibits Metastasis in Pancreatic Cancer via Degradation of Ferritin Heavy Chain and Mutant p53.
    Junhui Li, Rati Lama, Samuel L Galster, Joseph R Inigo, Jin Wu, Dhyan Chandra, Sherry R Chemler, Xinjiang Wang.
      High frequency of KRAS and TP53 mutations is a unique genetic feature of pancreatic ductal adenocarcinoma (PDAC). TP53 mutation not only renders PDAC resistance to chemotherapies but also drives PDAC invasiveness. Therapies targeting activating mutant KRAS are not available and the outcomes of current PDAC treatment are extremely poor. Here we report that MMRi62, initially identified as an MDM2-MDM4-targeting small molecule with p53-independent pro-apoptotic activity, shows anti-PDAC activity in vitro and in vivo. We show that MMRi62 inhibits proliferation, clonogenic and spheroid growth of PDAC cells by induction of cell death. MMRi62-induced cell death in PDAC is characteristic of ferroptosis which is associated with increased autophagy, increased reactive oxygen species and lysosomal degradation of NCOA4 and Ferritin Heavy Chain (FTH1). In addition to induced degradation of FTH1, MMRi62 also induces proteasomal degradation of mutant p53. Interestingly, MMRi62-induced ferroptosis occurs in PDAC cell lines harboring either KRAS and TP53 double mutations or single TP53 mutation. In orthotopic xenograft PDAC mouse models, MMRi62 was capable of inhibiting tumor growth in mice associated with downregulation of NCOA4 and mutant p53 in vivo. Strikingly, MMRi62 completely abrogated metastasis of orthotopic tumors to distant organs, which is consistent with MMRi62's ability to inhibit cell migration and invasion in vitro. These findings identified MMRi62 as a novel ferroptosis inducer capable of suppressing PDAC growth and overcoming metastasis.
    DOI:  https://doi.org/10.1158/1535-7163.MCT-21-0728
  15. Nucleic Acids Res. 2022 Feb 07. pii: gkac047. [Epub ahead of print]
    The transcriptional elongation factor CTR9 demarcates PRC2-mediated H3K27me3 domains by altering PRC2 subtype equilibrium.
    Ngai Ting Chan, Junfeng Huang, Gui Ma, Hao Zeng, Kristine Donahue, Yidan Wang, Lingjun Li, Wei Xu.
      CTR9 is the scaffold subunit in polymerase-associated factor complex (PAFc), a multifunctional complex employed in multiple steps of RNA Polymerase II (RNAPII)-mediated transcription. CTR9/PAFc is well known as an evolutionarily conserved elongation factor that regulates gene activation via coupling with histone modifications enzymes. However, little is known about its function to restrain repressive histone markers. Using inducible and stable CTR9 knockdown breast cancer cell lines, we discovered that the H3K27me3 levels are strictly controlled by CTR9. Quantitative profiling of histone modifications revealed a striking increase of H3K27me3 levels upon loss of CTR9. Moreover, loss of CTR9 leads to genome-wide expansion of H3K27me3, as well as increased recruitment of PRC2 on chromatin, which can be reversed by CTR9 restoration. Further, CTR9 depletion triggers a PRC2 subtype switch from the less active PRC2.2, to the more active PRC2.1 with higher methyltransferase activity. As a consequence, CTR9 depletion generates vulnerability that renders breast cancer cells hypersensitive to PRC2 inhibitors. Our findings that CTR9 demarcates PRC2-mediated H3K27me3 levels and genomic distribution provide a unique mechanism that explains the transition from transcriptionally active chromatin states to repressive chromatin states and sheds light on the biological functions of CTR9 in development and cancer.
    DOI:  https://doi.org/10.1093/nar/gkac047
  16. Cell Rep. 2022 Feb 08. pii: S2211-1247(22)00065-1. [Epub ahead of print]38(6): 110349
    PD-L1 promotes myofibroblastic activation of hepatic stellate cells by distinct mechanisms selective for TGF-β receptor I versus II.
    Liankang Sun, Yuanguo Wang, Xianghu Wang, Amaia Navarro-Corcuera, Sumera Ilyas, Nidhi Jalan-Sakrikar, Can Gan, Xinyi Tu, Yu Shi, Kangsheng Tu, Qingguang Liu, Zhenkun Lou, Haidong Dong, Arlene H Sharpe, Vijay H Shah, Ningling Kang.
      Intrahepatic cholangiocarcinoma (ICC) contains abundant myofibroblasts derived from hepatic stellate cells (HSCs) through an activation process mediated by TGF-β. To determine the role of programmed death-ligand 1 (PD-L1) in myofibroblastic activation of HSCs, we disrupted PD-L1 of HSCs by shRNA or anti-PD-L1 antibody. We find that PD-L1, produced by HSCs, is required for HSC activation by stabilizing TGF-β receptors I (TβRI) and II (TβRII). While the extracellular domain of PD-L1 (amino acids 19-238) targets TβRII protein to the plasma membrane and protects it from lysosomal degradation, a C-terminal 260-RLRKGR-265 motif on PD-L1 protects TβRI mRNA from degradation by the RNA exosome complex. PD-L1 is required for HSC expression of tumor-promoting factors, and targeting HSC PD-L1 by shRNA or Cre/loxP recombination suppresses HSC activation and ICC growth in mice. Thus, myofibroblast PD-L1 can modulate the tumor microenvironment and tumor growth by a mechanism independent of immune suppression.
    Keywords:  RNA immunoprecipitation; RNA sequencing; TGF-β receptor trafficking; biotinylation; cancer desmoplastic reaction; cancer-associated fibroblasts; conditional knockout mice; exosome component 10; ubiquitination; α-smooth muscle actin
    DOI:  https://doi.org/10.1016/j.celrep.2022.110349
  17. Front Cell Dev Biol. 2022 ;10 826379
    Low-Density Lipoprotein Internalization, Degradation and Receptor Recycling Along Membrane Contact Sites.
    Mohammad Majharul Islam, Iryna Hlushchenko, Simon G Pfisterer.
      Low-density lipoprotein (LDL) internalization, degradation, and receptor recycling is a fundamental process underlying hypercholesterolemia, a high blood cholesterol concentration, affecting more than 40% of the western population. Membrane contact sites influence endosomal dynamics, plasma membrane lipid composition, and cellular cholesterol distribution. However, if we focus on LDL-related trafficking events we mostly discuss them in an isolated fashion, without cellular context. It is our goal to change this perspective and to highlight that all steps from LDL internalization to receptor recycling are likely associated with dynamic membrane contact sites in which endosomes engage with the endoplasmic reticulum and other organelles.
    Keywords:  endosomal degradation; endosomal recycling; hypercholesterolemia; low-density lipoprotein (LDL); low-density lipoprotein receptor (LDLR); membrane contact site
    DOI:  https://doi.org/10.3389/fcell.2022.826379
  18. Nat Rev Cancer. 2022 Feb 11.
    Liquid-liquid phase separation drives cellular function and dysfunction in cancer.
    Sohum Mehta, Jin Zhang.
      Cancer is a disease of uncontrollably reproducing cells. It is governed by biochemical pathways that have escaped the regulatory bounds of normal homeostatic balance. This balance is maintained through precise spatiotemporal regulation of these pathways. The formation of biomolecular condensates via liquid-liquid phase separation (LLPS) has recently emerged as a widespread mechanism underlying the spatiotemporal coordination of biological activities in cells. Biomolecular condensates are widely observed to directly regulate key cellular processes involved in cancer cell pathology, and the dysregulation of LLPS is increasingly implicated as a previously hidden driver of oncogenic activity. In this Perspective, we discuss how LLPS shapes the biochemical landscape of cancer cells.
    DOI:  https://doi.org/10.1038/s41568-022-00444-7
  19. Proc Natl Acad Sci U S A. 2022 Feb 15. pii: e2120404119. [Epub ahead of print]119(7):
    Structural mechanism of allosteric activation of TRPML1 by PI(3,5)P2 and rapamycin.
    Ninghai Gan, Yan Han, Weizhong Zeng, Yan Wang, Jing Xue, Youxing Jiang.
      Transient receptor potential mucolipin 1 (TRPML1) is a Ca2+-permeable, nonselective cation channel ubiquitously expressed in the endolysosomes of mammalian cells and its loss-of-function mutations are the direct cause of type IV mucolipidosis (MLIV), an autosomal recessive lysosomal storage disease. TRPML1 is a ligand-gated channel that can be activated by phosphatidylinositol 3,5-bisphosphate [PI(3,5)P2] as well as some synthetic small-molecule agonists. Recently, rapamycin has also been shown to directly bind and activate TRPML1. Interestingly, both PI(3,5)P2 and rapamycin have low efficacy in channel activation individually but together they work cooperatively and activate the channel with high potency. To reveal the structural basis underlying the synergistic activation of TRPML1 by PI(3,5)P2 and rapamycin, we determined the high-resolution cryoelectron microscopy (cryo-EM) structures of the mouse TRPML1 channel in various states, including apo closed, PI(3,5)P2-bound closed, and PI(3,5)P2/temsirolimus (a rapamycin analog)-bound open states. These structures, combined with electrophysiology, elucidate the molecular details of ligand binding and provide structural insight into how the TRPML1 channel integrates two distantly bound ligand stimuli and facilitates channel opening.
    Keywords:  PI(3,5)P2; TRPML1; lysosomal channel; rapamycin
    DOI:  https://doi.org/10.1073/pnas.2120404119
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