bims-pideca Biomed News
on Class IA PI3K signalling in development and cancer
Issue of 2020–04–12
seventeen papers selected by
Ralitsa Radostinova Madsen, University College London
  1. Mechanistic basis for PI3K inhibitor antitumor activity and adverse reactions in advanced breast cancer.
  2. IMPDH inhibitors for antitumor therapy in tuberous sclerosis complex.
  3. Everolimus versus alpelisib in advanced hormone receptor-positive HER2-negative breast cancer: targeting different nodes of the PI3K/AKT/mTORC1 pathway with different clinical implications.
  4. Metabolic Heterogeneity of Cancer Cells: An Interplay between HIF-1, GLUTs, and AMPK.
  5. Quantitative proteomic landscape of metaplastic breast carcinoma pathological subtypes and their relationship to triple-negative tumors.
  6. Roles of the PI3K/AKT/mTOR signalling pathways in neurodegenerative diseases and tumours.
  7. Parental metabolic syndrome epigenetically reprograms offspring hepatic lipid metabolism in mice.
  8. Elevated levels of Drosophila Wdr62 promote glial cell growth and proliferation through AURKA signalling to AKT and MYC.
  9. Synergistic Inhibition of Kinase Pathways Overcomes Resistance of Colorectal Cancer Spheroids to Cyclic Targeted Therapies.
  10. Prolonged mitosis results in structurally aberrant and over-elongated centrioles.
  11. Metabolic reprogramming and cancer progression.
  12. Ribosomal Protein S6 Hypofunction in Postmortem Human Brain Links mTORC1-Dependent Signaling and Schizophrenia.
  13. Pretargeted delivery of PI3K/mTOR small-molecule inhibitor-loaded nanoparticles for treatment of non-Hodgkin's lymphoma.
  14. FBXO22 degrades nuclear PTEN to promote tumorigenesis.
  15. Stress-mediated exit to quiescence restricted by increasing persistence in CDK4/6 activation.
  16. Selective organ targeting (SORT) nanoparticles for tissue-specific mRNA delivery and CRISPR-Cas gene editing.
  17. Organoid cultures from normal and cancer-prone human breast tissues preserve complex epithelial lineages.
  1. Breast Cancer Res Treat. 2020 Apr 09.
    Mechanistic basis for PI3K inhibitor antitumor activity and adverse reactions in advanced breast cancer.
    Pamela R Drullinsky, Sara A Hurvitz.
       PURPOSE: The phosphatidylinositol 3-kinase (PI3K) pathway is involved in several physiological processes, including glucose metabolism, cell proliferation, and cell growth. Hyperactivation of this signaling pathway has been associated with tumorigenesis and resistance to treatment in various cancer types. Mutations that activate PIK3CA, encoding the PI3K isoform p110α, are common in breast cancer, particularly in the hormone receptor-positive (HR+), human epidermal growth factor receptor-2-negative (HER2-) subtype. A number of PI3K inhibitors have been developed and evaluated for potential clinical use in combinations targeting multiple signaling pathways in cancer. The purpose of this review is to provide an overview of PI3K inhibitor mechanisms of action for antitumor activity and adverse events in advanced breast cancer (ABC).
    METHODS: Published results from phase 3 trials evaluating the efficacy and safety of PI3K inhibitors in patients with ABC and relevant literature were reviewed.
    RESULTS: Although PI3K inhibitors have been shown to prolong progression-free survival (PFS), the therapeutic index is often unfavorable. Adverse events, such as hyperglycemia, rash, and diarrhea are frequently observed in these patients. In particular, hyperglycemia is intrinsically linked to the inhibition of PI3Kα, a key mediator of insulin signaling. Off-target effects, including mood disorders and liver toxicity, have also been associated with some PI3K inhibitors.
    CONCLUSION: Recent clinical trial results show that specifically targeting PI3Kα can improve PFS and clinical benefit. Broad inhibition of class I PI3Ks appears to result in an unfavorable safety profile due to off-target effects, limiting the clinical utility of the early PI3K inhibitors.
    Keywords:  Advanced breast cancer; Hyperglycemia; PI3K; PIK3CA
    DOI:  https://doi.org/10.1007/s10549-020-05618-1
  2. JCI Insight. 2020 Apr 09. pii: 135071. [Epub ahead of print]5(7):
    IMPDH inhibitors for antitumor therapy in tuberous sclerosis complex.
    Alexander J Valvezan, Molly C McNamara, Spencer K Miller, Margaret E Torrence, John M Asara, Elizabeth P Henske, Brendan D Manning.
      Recent studies in distinct preclinical tumor models have established the nucleotide synthesis enzyme inosine-5'-monophosphate dehydrogenase (IMPDH) as a viable target for antitumor therapy. IMPDH inhibitors have been used clinically for decades as safe and effective immunosuppressants. However, the potential to repurpose these pharmacological agents for antitumor therapy requires further investigation, including direct comparisons of available compounds. Therefore, we tested structurally distinct IMPDH inhibitors in multiple cell and mouse tumor models of the genetic tumor syndrome tuberous sclerosis complex (TSC). TSC-associated tumors are driven by uncontrolled activation of the growth-promoting protein kinase complex mechanistic target of rapamycin (mTOR) complex 1 (mTORC1), which is also aberrantly activated in the majority of sporadic cancers. Despite eliciting similar immunosuppressive effects, the IMPDH inhibitor mizoribine, used clinically throughout Asia, demonstrated far superior antitumor activity compared with the FDA-approved IMPDH inhibitor mycophenolate mofetil (or CellCept, a prodrug of mycophenolic acid). When compared directly to the mTOR inhibitor rapamycin, mizoribine treatment provided a more durable antitumor response associated with tumor cell death. These results provide preclinical support for repurposing mizoribine, over other IMPDH inhibitors, as an alternative to mTOR inhibitors for the treatment of TSC-associated tumors and possibly other tumors featuring uncontrolled mTORC1 activity.
    Keywords:  Cancer; Genetic diseases; Metabolism; Therapeutics; Tumor suppressors
    DOI:  https://doi.org/10.1172/jci.insight.135071
  3. Breast Cancer Res. 2020 04 06. 22(1): 33
    Everolimus versus alpelisib in advanced hormone receptor-positive HER2-negative breast cancer: targeting different nodes of the PI3K/AKT/mTORC1 pathway with different clinical implications.
    Claudio Vernieri, Francesca Corti, Federico Nichetti, Francesca Ligorio, Sara Manglaviti, Emma Zattarin, Carmen G Rea, Giuseppe Capri, Giulia V Bianchi, Filippo de Braud.
       BACKGROUND: The PI3K/AKT/mTORC1 axis is implicated in hormone receptor-positive HER2-negative metastatic breast cancer (HR+ HER2- mBC) resistance to anti-estrogen treatments. Based on results of the BOLERO-2 trial, the mTORC1 inhibitor everolimus in combination with the steroidal aromatase inhibitor (AI) exemestane has become a standard treatment for patients with HR+ HER2- mBC resistant to prior non-steroidal AI therapy. In the recent SOLAR-1 trial, the inhibitor of the PI3K alpha subunit (p110α) alpelisib in combination with fulvestrant prolonged progression-free survival (PFS) when compared to fulvestrant alone in patients with PIK3CA-mutated HR+ HER2- mBC that progressed after/on previous AI treatment. Therefore, two different molecules targeting the PI3K/AKT/mTORC1 axis, namely everolimus and alpelisib, are available for patients progressing on/after previous AI treatment, but it is unclear how to optimize their use in the clinical practice. Here, we reviewed the available clinical evidence deriving from the BOLERO-2 and SOLAR-1 trials to compare efficacy and safety profiles of everolimus and alpelisib in advanced HR+ HER2- BC treatment. Adding either compound to standard endocrine therapy provided similar absolute and relative PFS advantage. In the SOLAR-1 trial, a 76% incidence of grade (G) 3 or 4 (G3/G4) adverse events was reported, while G3/G4 toxicities occurred in 42% of patients in the BOLERO-2 trial. While alpelisib was only effective in patients with PIK3CA-mutated neoplasms, retrospective analyses indicate that everolimus improves exemestane efficacy independently of PIK3CA mutational status.
    CONCLUSIONS: Based on the available efficacy and safety data, the "new" alpelisib may be burdened by higher incidence of severe adverse events, higher costs, and anticancer efficacy that is limited to PIK3CA-mutated tumors when compared to the "old" everolimus. Therefore, the everolimus-exemestane combination remains an effective and reasonably well-tolerated therapeutic option for HR+ HER2- mBC patients progressing after/on previous AI treatment, independently of PIK3CA mutational status.
    Keywords:  Advanced breast cancer; Alpelisib; Efficacy comparisons; Endocrine therapy; Everolimus; Hormone receptor-positive breast cancer; PI3K; PIK3CA mutations; mTORC1
    DOI:  https://doi.org/10.1186/s13058-020-01271-0
  4. Cancers (Basel). 2020 Apr 02. pii: E862. [Epub ahead of print]12(4):
    Metabolic Heterogeneity of Cancer Cells: An Interplay between HIF-1, GLUTs, and AMPK.
    Nurbubu T Moldogazieva, Innokenty M Mokhosoev, Alexander A Terentiev.
      It has been long recognized that cancer cells reprogram their metabolism under hypoxia conditions due to a shift from oxidative phosphorylation (OXPHOS) to glycolysis in order to meet elevated requirements in energy and nutrients for proliferation, migration, and survival. However, data accumulated over recent years has increasingly provided evidence that cancer cells can revert from glycolysis to OXPHOS and maintain both reprogrammed and oxidative metabolism, even in the same tumor. This phenomenon, denoted as cancer cell metabolic plasticity or hybrid metabolism, depends on a tumor micro-environment that is highly heterogeneous and influenced by an intensity of vasculature and blood flow, oxygen concentration, and nutrient and energy supply, and requires regulatory interplay between multiple oncogenes, transcription factors, growth factors, and reactive oxygen species (ROS), among others. Hypoxia-inducible factor-1 (HIF-1) and AMP-activated protein kinase (AMPK) represent key modulators of a switch between reprogrammed and oxidative metabolism. The present review focuses on cross-talks between HIF-1, glucose transporters (GLUTs), and AMPK with other regulatory proteins including oncogenes such as c-Myc, p53, and KRAS; growth factor-initiated protein kinase B (PKB)/Akt, phosphatydyl-3-kinase (PI3K), and mTOR signaling pathways; and tumor suppressors such as liver kinase B1 (LKB1) and TSC1 in controlling cancer cell metabolism. The multiple switches between metabolic pathways can underlie chemo-resistance to conventional anti-cancer therapy and should be taken into account in choosing molecular targets to discover novel anti-cancer drugs.
    Keywords:  AMPK; GLUTs; HIF-1; OXPHOS; cancer metabolism
    DOI:  https://doi.org/10.3390/cancers12040862
  5. Nat Commun. 2020 Apr 07. 11(1): 1723
    Quantitative proteomic landscape of metaplastic breast carcinoma pathological subtypes and their relationship to triple-negative tumors.
    Sabra I Djomehri, Maria E Gonzalez, Felipe da Veiga Leprevost, Shilpa R Tekula, Hui-Yin Chang, Marissa J White, Ashley Cimino-Mathews, Boris Burman, Venkatesha Basrur, Pedram Argani, Alexey I Nesvizhskii, Celina G Kleer.
      Metaplastic breast carcinoma (MBC) is a highly aggressive form of triple-negative cancer (TNBC), defined by the presence of metaplastic components of spindle, squamous, or sarcomatoid histology. The protein profiles underpinning the pathological subtypes and metastatic behavior of MBC are unknown. Using multiplex quantitative tandem mass tag-based proteomics we quantify 5798 proteins in MBC, TNBC, and normal breast from 27 patients. Comparing MBC and TNBC protein profiles we show MBC-specific increases related to epithelial-to-mesenchymal transition and extracellular matrix, and reduced metabolic pathways. MBC subtypes exhibit distinct upregulated profiles, including translation and ribosomal events in spindle, inflammation- and apical junction-related proteins in squamous, and extracellular matrix proteins in sarcomatoid subtypes. Comparison of the proteomes of human spindle MBC with mouse spindle (CCN6 knockout) MBC tumors reveals a shared spindle-specific signature of 17 upregulated proteins involved in translation and 19 downregulated proteins with roles in cell metabolism. These data identify potential subtype specific MBC biomarkers and therapeutic targets.
    DOI:  https://doi.org/10.1038/s41467-020-15283-z
  6. Cell Biosci. 2020 ;10 54
    Roles of the PI3K/AKT/mTOR signalling pathways in neurodegenerative diseases and tumours.
    Fei Xu, Lixin Na, Yanfei Li, Linjun Chen.
      The PI3 K/AKT/mTOR signalling pathway plays an important role in the regulation of signal transduction and biological processes such as cell proliferation, apoptosis, metabolism and angiogenesis. Compared with those of other signalling pathways, the components of the PI3K/AKT/mTOR signalling pathway are complicated. The regulatory mechanisms and biological functions of the PI3K/AKT/mTOR signalling pathway are important in many human diseases, including ischaemic brain injury, neurodegenerative diseases, and tumours. PI3K/AKT/mTOR signalling pathway inhibitors include single-component and dual inhibitors. Numerous PI3K inhibitors have exhibited good results in preclinical studies, and some have been clinically tested in haematologic malignancies and solid tumours. In this review, we briefly summarize the results of research on the PI3K/AKT/mTOR pathway and discuss the structural composition, activation, communication processes, regulatory mechanisms and biological functions of the PI3K/AKT/mTOR signalling pathway in the pathogenesis of neurodegenerative diseases and tumours.
    Keywords:  Ischaemic brain injury; Neurodegenerative diseases; PI3K/AKT/mTOR signalling pathway; Regulatory mechanism; Tumour
    DOI:  https://doi.org/10.1186/s13578-020-00416-0
  7. J Clin Invest. 2020 Apr 06. pii: 127502. [Epub ahead of print]
    Parental metabolic syndrome epigenetically reprograms offspring hepatic lipid metabolism in mice.
    Dario F De Jesus, Kazuki Orime, Dorota Kaminska, Tomohiko Kimura, Giorgio Basile, Chih-Hao Wang, Larissa Haertle, Renzo Riemens, Natalie K Brown, Jiang Hu, Ville Männistö, Amélia M Silva, Ercument Dirice, Yu-Hua Tseng, Thomas Haaf, Jussi Pihlajamäki, Rohit N Kulkarni.
      The prevalence of nonalcoholic fatty liver disease (NAFLD) is increasing worldwide. Although gene-environment interactions have been implicated in the etiology of several disorders, the impact of paternal and/or maternal metabolic syndrome on the clinical phenotypes of offspring and the underlying genetic and epigenetic contributors of NAFLD have not been fully explored. To this end, we used the liver-specific insulin receptor knockout (LIRKO) mouse, a unique nondietary model manifesting 3 hallmarks that confer high risk for the development of NAFLD: hyperglycemia, insulin resistance, and dyslipidemia. We report that parental metabolic syndrome epigenetically reprograms members of the TGF-β family, including neuronal regeneration-related protein (NREP) and growth differentiation factor 15 (GDF15). NREP and GDF15 modulate the expression of several genes involved in the regulation of hepatic lipid metabolism. In particular, NREP downregulation increases the protein abundance of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) and ATP-citrate lyase (ACLY) in a TGF-β receptor/PI3K/protein kinase B-dependent manner, to regulate hepatic acetyl-CoA and cholesterol synthesis. Reduced hepatic expression of NREP in patients with NAFLD and substantial correlations between low serum NREP levels and the presence of steatosis and nonalcoholic steatohepatitis highlight the clinical translational relevance of our findings in the context of recent preclinical trials implicating ACLY in NAFLD progression.
    Keywords:  Development; Diabetes; Embryonic development; Epigenetics; Hepatology
    DOI:  https://doi.org/10.1172/JCI127502
  8. Biochim Biophys Acta Mol Cell Res. 2020 Apr 01. pii: S0167-4889(20)30071-9. [Epub ahead of print] 118713
    Elevated levels of Drosophila Wdr62 promote glial cell growth and proliferation through AURKA signalling to AKT and MYC.
    Belal Shohayeb, Naomi Mitchell, S Sean Millard, Leonie M Quinn, Dominic C H Ng.
      WD40-Repeat Protein 62 (WDR62) is required to maintain neural and glial cell populations during embryonic brain growth. Although elevated expression of WDR62 is frequently associated with several tumour types, potential effects of excess WDR62 on proliferative growth remain undefined. Here, we demonstrate that glia specific overexpression of WDR62 in Drosophila larval brains resulted in increased cell size, over-proliferation and increased brain volume, without overt disruption of tissue organization. We further demonstrate WDR62 promoted over-proliferation and brain overgrowth by activating AURKA and pAKT signalling to increase MYC function in glial cells. Together these data suggest WDR62 normally functions in the glial lineage to activate oncogenic signalling networks, promoting proliferation and brain overgrowth.
    Keywords:  Cell growth; Cell proliferation; Glia; MYC; Signal transduction; WD40 domains
    DOI:  https://doi.org/10.1016/j.bbamcr.2020.118713
  9. ACS Pharmacol Transl Sci. 2019 Aug 09. 2(4): 275-284
    Synergistic Inhibition of Kinase Pathways Overcomes Resistance of Colorectal Cancer Spheroids to Cyclic Targeted Therapies.
    Pradip Shahi Thakuri, Megha Gupta, Ramila Joshi, Sunil Singh, Hossein Tavana.
      Cancer cells often adapt to single-agent treatments with chemotherapeutics. Activation of alternative survival pathways is a major mechanism of drug resistance. A potential approach to block this feedback signaling is using combination treatments of a pair of drugs, although toxicity has been a limiting factor. Preclinical tumor models to identify mechanisms of drug resistance and determine low but effective combination doses are critical to effectively suppress tumor growth with reduced toxicity to patients. Using our aqueous two-phase system microtechnology, we developed colorectal tumor spheroids in high-throughput and evaluated resistance of cancer cells to three mitogen-activated protein kinase inhibitors (MAPKi) in long-term cyclic treatments. Our quantitative analysis showed that the efficacy of MAPKi significantly reduced over time, leading to an increase in proliferation of HCT116 colorectal cancer cells and growth of spheroids. We established that resistance was due to feedback activation of PI3K/AKT/mTOR pathway. Using high-throughput, dose-dependent combinations of each MAPKi and a PI3K/mTOR inhibitor, we identified low-dose, synergistic combinations that blocked resistance to MAPKi and effectively suppressed the growth of colorectal tumor spheroids in long-term treatments. Our approach to study drug resistance offers the potential to determine high priority treatments to test in animal models.
    DOI:  https://doi.org/10.1021/acsptsci.9b00042
  10. J Cell Biol. 2020 Jun 01. pii: e201910019. [Epub ahead of print]219(6):
    Prolonged mitosis results in structurally aberrant and over-elongated centrioles.
    Dong Kong, Natalie Sahabandu, Catherine Sullenberger, Alejandra Vásquez-Limeta, Delgermaa Luvsanjav, Kimberly Lukasik, Jadranka Loncarek.
      Centrioles are precisely built microtubule-based structures that assemble centrosomes and cilia. Aberrations in centriole structure are common in tumors, yet how these aberrations arise is unknown. Analysis of centriole structure is difficult because it requires demanding electron microscopy. Here we employ expansion microscopy to study the origins of centriole structural aberrations in large populations of human cells. We discover that centrioles do not have an elongation monitoring mechanism, which renders them prone to over-elongation, especially during prolonged mitosis induced by various factors, importantly including supernumerary centrioles. We identify that mitotic centriole over-elongation is dependent on mitotic Polo-like kinase 1, which we uncover as a novel regulator of centriole elongation in human cycling cells. While insufficient Plk1 levels lead to the formation of shorter centrioles lacking a full set of microtubule triplets, its overactivity results in over-elongated and structurally aberrant centrioles. Our data help explain the origin of structurally aberrant centrioles and why centriole numerical and structural defects coexist in tumors.
    DOI:  https://doi.org/10.1083/jcb.201910019
  11. Science. 2020 Apr 10. pii: eaaw5473. [Epub ahead of print]368(6487):
    Metabolic reprogramming and cancer progression.
    Brandon Faubert, Ashley Solmonson, Ralph J DeBerardinis.
      Metabolic reprogramming is a hallmark of malignancy. As our understanding of the complexity of tumor biology increases, so does our appreciation of the complexity of tumor metabolism. Metabolic heterogeneity among human tumors poses a challenge to developing therapies that exploit metabolic vulnerabilities. Recent work also demonstrates that the metabolic properties and preferences of a tumor change during cancer progression. This produces distinct sets of vulnerabilities between primary tumors and metastatic cancer, even in the same patient or experimental model. We review emerging concepts about metabolic reprogramming in cancer, with particular attention on why metabolic properties evolve during cancer progression and how this information might be used to develop better therapeutic strategies.
    DOI:  https://doi.org/10.1126/science.aaw5473
  12. Front Pharmacol. 2020 ;11 344
    Ribosomal Protein S6 Hypofunction in Postmortem Human Brain Links mTORC1-Dependent Signaling and Schizophrenia.
    Inés Ibarra-Lecue, Rebeca Diez-Alarcia, Benito Morentin, J Javier Meana, Luis F Callado, Leyre Urigüen.
      The mechanistic target of rapamycin (also known as mammalian target of rapamycin) (mTOR)-dependent signaling pathway plays an important role in protein synthesis, cell growth, and proliferation, and has been linked to the development of the central nervous system. Recent studies suggest that mTOR signaling pathway dysfunction could be involved in the etiopathogenesis of schizophrenia. The main goal of this study was to evaluate the status of mTOR signaling pathway in postmortem prefrontal cortex (PFC) samples of subjects with schizophrenia. For this purpose, we quantified the protein expression and phosphorylation status of the mTOR downstream effector ribosomal protein S6 as well as other pathway interactors such as Akt and GSK3β. Furthermore, we quantified the status of these proteins in the brain cortex of rats chronically treated with the antipsychotics haloperidol, clozapine, or risperidone. We found a striking decrease in the expression of total S6 and in its active phosphorylated form phospho-S6 (Ser235/236) in the brain of subjects with schizophrenia compared to matched controls. The chronic treatment with the antipsychotics haloperidol and clozapine affected both the expression of GSK3β and the activation of Akt [phospho-Akt (Ser473)] in rat brain cortex, while no changes were observed in S6 and phospho-S6 (Ser235/236) protein expression with any antipsychotic treatment. These findings provide further evidence for the involvement of the mTOR-dependent signaling pathway in schizophrenia and suggest that a hypofunctional S6 may have a role in the etiopathogenesis of this disorder.
    Keywords:  antipsychotics; mTORC1; postmortem tissue; ribosomal protein S6; schizophrenia
    DOI:  https://doi.org/10.3389/fphar.2020.00344
  13. Sci Adv. 2020 Apr;6(14): eaaz9798
    Pretargeted delivery of PI3K/mTOR small-molecule inhibitor-loaded nanoparticles for treatment of non-Hodgkin's lymphoma.
    Kin Man Au, Andrew Z Wang, Steven I Park.
      Overactivation of the PI3K/mTOR signaling has been identified in non-Hodgkin's lymphoma. BEZ235 is an effective dual PI3K/mTOR inhibitor, but it was withdrawn from early-phase clinical trials owing to poor solubility and on-target/off-tumor toxicity. Here, we developed a nanoparticle (NP)-based pretargeted system for the therapeutic delivery of BEZ235 to CD20- and HLA-DR-expressing lymphoma cells for targeted therapy. The pretargeted system is composed of dibenzocyclooctyne-functionalized anti-CD20 and anti-Lym1 antibodies as the tumor-targeting components and azide-functionalized BEZ235-encapsulated NPs as the effector drug carrier. Using lymphoma cell lines with different CD20 and HLA-DR antigen densities as examples, we demonstrate that the dual antibody pretargeted strategy effectively raises the number of NPs retained on the target tumor cells and improves the in vitro and in vivo antitumor activity of BEZ235 through the inhibition of the PI3K/mTOR pathway. Our data demonstrate that the NP-based pretargeted system improves the therapeutic window of small-molecule kinase inhibitor.
    DOI:  https://doi.org/10.1126/sciadv.aaz9798
  14. Nat Commun. 2020 Apr 06. 11(1): 1720
    FBXO22 degrades nuclear PTEN to promote tumorigenesis.
    Meng-Kai Ge, Na Zhang, Li Xia, Cheng Zhang, Shuang-Shu Dong, Zhan-Ming Li, Yan Ji, Min-Hua Zheng, Jing Sun, Guo-Qiang Chen, Shao-Ming Shen.
      Nuclear localization of PTEN is essential for its tumor suppressive role, and loss of nuclear PTEN is more prominent than cytoplasmic PTEN in many kinds of cancers. However, nuclear PTEN-specific regulatory mechanisms were rarely reported. Based on the finding that nuclear PTEN is more unstable than cytoplasmic PTEN, here we identify that F-box only protein 22 (FBXO22) induces ubiquitylation of nuclear but not cytoplasmic PTEN at lysine 221, which is responsible for the degradation of nuclear PTEN. FBXO22 plays a tumor-promoting role by ubiquitylating and degrading nuclear PTEN. In accordance, FBXO22 is overexpressed in various cancer types, and contributes to nuclear PTEN downregulation in colorectal cancer tissues. Cumulatively, our study reports the mechanism to specifically regulate the stability of nuclear PTEN, which would provide the opportunity for developing therapeutic strategies aiming to achieve complete reactivation of PTEN as a tumor suppressor.
    DOI:  https://doi.org/10.1038/s41467-020-15578-1
  15. Elife. 2020 Apr 07. pii: e44571. [Epub ahead of print]9
    Stress-mediated exit to quiescence restricted by increasing persistence in CDK4/6 activation.
    Hee Won Yang, Steven D Cappell, Ariel Jaimovich, Chad Liu, Mingyu Chung, Leighton H Daigh, Lindsey R Pack, Yilin Fan, Sergi Regot, Markus Covert, Tobias Meyer.
      Mammalian cells typically start the cell-cycle entry program by activating cyclin-dependent protein kinase 4/6 (CDK4/6). CDK4/6 activity is clinically relevant as mutations, deletions, and amplifications that increase CDK4/6 activity contribute to the progression of many cancers. However, when CDK4/6 is activated relative to CDK2 remained incompletely understood. Here we developed a reporter system to simultaneously monitor CDK4/6 and CDK2 activities in single cells and found that CDK4/6 activity increases rapidly before CDK2 activity gradually increases, and that CDK4/6 activity can be active after mitosis or inactive for variable time periods. Markedly, stress signals in G1 can rapidly inactivate CDK4/6 to return cells to quiescence but with reduced probability as cells approach S phase. Together, our study reveals a regulation of G1 length by temporary inactivation of CDK4/6 activity after mitosis, and a progressively increasing persistence in CDK4/6 activity that restricts cells from returning to quiescence as cells approach S phase.
    Keywords:  cell biology; human
    DOI:  https://doi.org/10.7554/eLife.44571
  16. Nat Nanotechnol. 2020 Apr 06.
    Selective organ targeting (SORT) nanoparticles for tissue-specific mRNA delivery and CRISPR-Cas gene editing.
    Qiang Cheng, Tuo Wei, Lukas Farbiak, Lindsay T Johnson, Sean A Dilliard, Daniel J Siegwart.
      CRISPR-Cas gene editing and messenger RNA-based protein replacement therapy hold tremendous potential to effectively treat disease-causing mutations with diverse cellular origin. However, it is currently impossible to rationally design nanoparticles that selectively target specific tissues. Here, we report a strategy termed selective organ targeting (SORT) wherein multiple classes of lipid nanoparticles are systematically engineered to exclusively edit extrahepatic tissues via addition of a supplemental SORT molecule. Lung-, spleen- and liver-targeted SORT lipid nanoparticles were designed to selectively edit therapeutically relevant cell types including epithelial cells, endothelial cells, B cells, T cells and hepatocytes. SORT is compatible with multiple gene editing techniques, including mRNA, Cas9 mRNA/single guide RNA and Cas9 ribonucleoprotein complexes, and is envisioned to aid the development of protein replacement and gene correction therapeutics in targeted tissues.
    DOI:  https://doi.org/10.1038/s41565-020-0669-6
  17. Nat Commun. 2020 Apr 06. 11(1): 1711
    Organoid cultures from normal and cancer-prone human breast tissues preserve complex epithelial lineages.
    Jennifer M Rosenbluth, Ron C J Schackmann, G Kenneth Gray, Laura M Selfors, Carman Man-Chung Li, Mackenzie Boedicker, Hendrik J Kuiken, Andrea Richardson, Jane Brock, Judy Garber, Deborah Dillon, Norman Sachs, Hans Clevers, Joan S Brugge.
      Recently, organoid technology has been used to generate a large repository of breast cancer organoids. Here we present an extensive evaluation of the ability of organoid culture technology to preserve complex stem/progenitor and differentiated cell types via long-term propagation of normal human mammary tissues. Basal/stem and luminal progenitor cells can differentiate in culture to generate mature basal and luminal cell types, including ER+ cells that have been challenging to maintain in culture. Cells associated with increased cancer risk can also be propagated. Single-cell analyses of matched organoid cultures and native tissues by mass cytometry for 38 markers provide a higher resolution representation of the multiple mammary epithelial cell types in the organoids, and demonstrate that protein expression patterns of the tissue of origin can be preserved in culture. These studies indicate that organoid cultures provide a valuable platform for studies of mammary differentiation, transformation, and breast cancer risk.
    DOI:  https://doi.org/10.1038/s41467-020-15548-7
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