bims-pideca Biomed News
on Class IA PI3K signalling in development and cancer
Issue of 2019‒12‒08
fifteen papers selected by
Ralitsa Radostinova Madsen
University College London Cancer Institute

  1. Am J Physiol Endocrinol Metab. 2019 Dec 03.
      Growth factor receptor-bound 10 (Grb10) is an adaptor protein that binds to the insulin receptor, upon which insulin signaling and action is thought to be inhibited. Grb10 is also a substrate for the mechanistic target of rapamycin complex 1 (mTORC1) that mediates its feedback inhibition on phosphatidylinositide 3-kinase (PI3K)/Akt signaling. To characterize the function of Grb10 and its regulation by mTORC1 in human muscle, primary skeletal muscle cells were isolated from healthy lean young men and then induced to differentiate into myotubes. Knockdown of Grb10 enhanced insulin-induced PI3K/Akt signaling and glucose uptake in myotubes, reinforcing the notion underlying its function as a negative regulator of insulin action in human muscle. The increased insulin sensitivity responsiveness in Grb10-silenced myotubes was associated with higher abundance of the insulin receptor. Furthermore, insulin and amino acids independently and additively stimulated phosphorylation of Grb10 at Ser476. However, acute inhibition of mTORC1 with rapamycin blocked Grb10 Ser476 phosphorylation and repressed a negative-feedback loop on PI3K/Akt signaling that increased myotube responsiveness to insulin. Chronic rapamycin treatment reduced Grb10 protein abundance in conjunction with increased insulin receptor protein levels. Based on these findings, we propose that mTORC1 controls PI3K/Akt signaling through modulation of insulin receptor abundance by Grb10. These findings have potential implications for obesity-linked insulin resistance, as well as clinical use of mTORC1 inhibitors.
    Keywords:  Amino acids; Grb10; Insulin signaling; human myotubes; mechanistic target of rapamcin complex 1
  2. Exp Eye Res. 2019 Nov 28. pii: S0014-4835(19)30498-1. [Epub ahead of print] 107884
      Proliferative vitreoretinopathy (PVR) is a blinding fibrotic eye disease that develops in 8-10% of patients who undergo primary retinal detachment-reparative surgery and in 40-60% of patients with open-globe injury. At present, there is no pharmacological treatment for this devastating disease. Vitreal growth factors activate their respective receptors of cells in the vitreous, trigger their downstream signaling transduction (e.g. phosphoinositide 3 kinases (PI3Ks)/Akt), and drive cellular responses intrinsic to the pathogenesis of PVR. PI3Ks play a central role in experimental PVR. However, which isoform(s) are involved in PVR pathogenesis remain unknown. Herein, we show that p110δ, a catalytic subunit of receptor-regulated PI3K isoform δ, is highly expressed in epiretinal membranes from patients with PVR, and that idelalisib, a specific inhibitor of PI3Kδ, effectively inhibits vitreous-induced Akt activation, proliferation, migration and contraction of retinal pigment epithelial cells derived from an epiretinal membrane of a PVR patient. Small molecules of kinase inhibitors have shown great promise as a class of therapeutics for a variety of human diseases. The data herein suggest that idelalisib is a promising PVR prophylactic.
    Keywords:  Akt; Contraction; Idelalisib; Migration; PI3Kδ; PVR; Proliferation; Vitreous
  3. Biochem Pharmacol. 2019 Nov 27. pii: S0006-2952(19)30428-9. [Epub ahead of print] 113729
      The aim of this review is to summarize current available information about the role of PI3K/AKT/mTOR signaling in head and neck cancer as a potential target for new therapy options. 90% of all head and neck cancers are squamous cell carcinomas (HNSCC). The most common genetic alteration is inactivation of p16 gene which is cyclin dependent kinase inhibitor 2A. HNSCC are divided into human papilloma virus (HPV) related and HPV-negative carcinomas. HPV related carcinomas of patients who do not have a history of tobacco and alcohol consumption have better prognosis. Until now, HNSCC are treated with surgical removal of cancer tissue in primary region and lymph nodes combined with radiotherapy, cytostatic drugs and in some cases, epidermal growth factor receptor (EGFR) targeted antibody cetuximab and programmed death receptor-1 (PD-1) antibodies. PI3K/AKT/mTOR signaling is active in over 90% of HNSCC, as a result of EGFR activation (47%), phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) mutations (8.6%), PIK3CA amplifications (14.2%), phosphatidylinositol 3-kinase (PI3K) overexpression (27.2%) and phosphatase and tensin homolog (PTEN) mutation (10-15%). Activated PI3K/AKT/mTOR signaling is related to radiotherapy and cytostatic drug resistance, likely through enhanced DNA-repair mechanisms. Inhibitors against PI3K, AKT and mammalian target of rapamycin (mTOR) have remarkable effects on tumor cell proliferation and radiotherapy sensitization in cell cultures and mouse models. Nevertheless, feedback mechanisms, like activation of AKT after mTOR treatment, reduce efficiency. Therefore, combined therapy should be investigated. PI3K, AKT and mTOR inhibitors achieved tumor response in 5.3%, 2.8% and 31% when given as monotherapy, respectively. When combined to cytostatic drugs, 29.2% and 43.5% of all patients showed a response to PI3K and mTOR inhibitors, respectively. A study investigating everolimus (Rad001) with cisplatin and radiotherapy has reported promising 2-year progression free survival and overall survival rates of 85% and 92%. Further clinical trials should follow.
    Keywords:  Drug response; Head and neck cancer; Mutations; PI3K/AKT/mTOR signaling pathway; Survival; Therapeutics
  4. Cell Rep. 2019 Dec 03. pii: S2211-1247(19)31450-0. [Epub ahead of print]29(10): 3331-3348.e7
      Metformin is the front-line treatment for type 2 diabetes worldwide. It acts via effects on glucose and lipid metabolism in metabolic tissues, leading to enhanced insulin sensitivity. Despite significant effort, the molecular basis for metformin response remains poorly understood, with a limited number of specific biochemical pathways studied to date. To broaden our understanding of hepatic metformin response, we combine phospho-protein enrichment in tissue from genetically engineered mice with a quantitative proteomics platform to enable the discovery and quantification of basophilic kinase substrates in vivo. We define proteins whose binding to 14-3-3 are acutely regulated by metformin treatment and/or loss of the serine/threonine kinase, LKB1. Inducible binding of 250 proteins following metformin treatment is observed, 44% of which proteins bind in a manner requiring LKB1. Beyond AMPK, metformin activates protein kinase D and MAPKAPK2 in an LKB1-independent manner, revealing additional kinases that may mediate aspects of metformin response. Deeper analysis uncovered substrates of AMPK in endocytosis and calcium homeostasis.
    Keywords:  AMPK3; LKB1; PKD1; STIM1; aging; calcium; diabetes; kinases; liver; metformin
  5. Nat Commun. 2019 Dec 02. 10(1): 5486
      Protein oxidation sits at the intersection of multiple signalling pathways, yet the magnitude and extent of crosstalk between oxidation and other post-translational modifications remains unclear. Here, we delineate global changes in adipocyte signalling networks following acute oxidative stress and reveal considerable crosstalk between cysteine oxidation and phosphorylation-based signalling. Oxidation of key regulatory kinases, including Akt, mTOR and AMPK influences the fidelity rather than their absolute activation state, highlighting an unappreciated interplay between these modifications. Mechanistic analysis of the redox regulation of Akt identified two cysteine residues in the pleckstrin homology domain (C60 and C77) to be reversibly oxidized. Oxidation at these sites affected Akt recruitment to the plasma membrane by stabilizing the PIP3 binding pocket. Our data provide insights into the interplay between oxidative stress-derived redox signalling and protein phosphorylation networks and serve as a resource for understanding the contribution of cellular oxidation to a range of diseases.
  6. Nucleic Acids Res. 2019 Dec 04. pii: gkz1121. [Epub ahead of print]
      Genome editing typically involves recombination between donor nucleic acids and acceptor genomic sequences subjected to double-stranded DNA breaks (DSBs) made by programmable nucleases (e.g. CRISPR-Cas9). Yet, nucleases yield off-target mutations and, most pervasively, unpredictable target allele disruptions. Remarkably, to date, the untoward phenotypic consequences of disrupting allelic and non-allelic (e.g. pseudogene) sequences have received scant scrutiny and, crucially, remain to be addressed. Here, we demonstrate that gene-edited cells can lose fitness as a result of DSBs at allelic and non-allelic target sites and report that simultaneous single-stranded DNA break formation at donor and acceptor DNA by CRISPR-Cas9 nickases (in trans paired nicking) mostly overcomes such disruptive genotype-phenotype associations. Moreover, in trans paired nicking gene editing can efficiently and precisely add large DNA segments into essential and multiple-copy genomic sites. As shown herein by genotyping assays and high-throughput genome-wide sequencing of DNA translocations, this is achieved while circumventing most allelic and non-allelic mutations and chromosomal rearrangements characteristic of nuclease-dependent procedures. Our work demonstrates that in trans paired nicking retains target protein dosages in gene-edited cell populations and expands gene editing to chromosomal tracts previously not possible to modify seamlessly due to their recurrence in the genome or essentiality for cell function.
  7. Front Oncol. 2019 ;9 1231
      The mechanism through which oncogenic Ras activates its effectors is vastly important to resolve. If allostery is at play, then targeting allosteric pathways could help in quelling activation of MAPK (Raf/MEK/ERK) and PI3K (PI3K/Akt/mTOR) cell proliferation pathways. On the face of it, allosteric activation is reasonable: Ras binding perturbs the conformational ensembles of its effectors. Here, however, we suggest that at least for Raf, PI3K, and NORE1A (RASSF5), that is unlikely. Raf's long disordered linker dampens effective allosteric activation. Instead, we suggest that the high-affinity Ras-Raf binding relieves Raf's autoinhibition, shifting Raf's ensemble from the inactive to the nanocluster-mediated dimerized active state, as Ras also does for NORE1A. PI3K is recruited and allosterically activated by RTK (e.g., EGFR) at the membrane. Ras restrains PI3K's distribution and active site orientation. It stabilizes and facilitates PIP2 binding at the active site and increases the PI3K residence time at the membrane. Thus, RTKs allosterically activate PI3Kα; however, merging their action with Ras accomplishes full activation. Here we review their activation mechanisms in this light and draw attention to implications for their pharmacology.
    Keywords:  B-Raf; BRAF; K-Ras; KRas; NORE1A; allosteric; allostery
  8. Nat Commun. 2019 Dec 06. 10(1): 5604
      Increased glucose uptake and metabolism is a prominent phenotype of most cancers, but efforts to clinically target this metabolic alteration have been challenging. Here, we present evidence that lactoylglutathione (LGSH), a byproduct of methylglyoxal detoxification, is elevated in both human and murine non-small cell lung cancers (NSCLC). Methylglyoxal is a reactive metabolite byproduct of glycolysis that reacts non-enzymatically with nucleophiles in cells, including basic amino acids, and reduces cellular fitness. Detoxification of methylglyoxal requires reduced glutathione (GSH), which accumulates to high levels in NSCLC relative to normal lung. Ablation of the methylglyoxal detoxification enzyme glyoxalase I (Glo1) potentiates methylglyoxal sensitivity and reduces tumor growth in mice, arguing that targeting pathways involved in detoxification of reactive metabolites is an approach to exploit the consequences of increased glucose metabolism in cancer.
  9. Breast Cancer Res. 2019 Dec 04. 21(1): 135
      BACKGROUND: Endocrine therapies are still the main strategy for the treatment of oestrogen receptor-positive (ER+) breast cancers (BC), but resistance remains problematic. Cross-talk between ER and PI3K/AKT/mTORC has been associated with ligand-independent transcription of ER. We have previously reported the anti-proliferative effects of the combination of everolimus (an mTORC1 inhibitor) with endocrine therapy in resistance models, but potential routes of escape via AKT signalling can lead to resistance; therefore, the use of dual mTORC1/2 inhibitors has met with significant interest.METHODS: To address this, we tested the effect of vistusertib, a dual mTORC1 and mTORC2 inhibitor, in a panel of endocrine-resistant and endocrine-sensitive ER+ BC cell lines, with varying PTEN, PIK3CA and ESR1 mutation status. End-points included proliferation, cell signalling, cell cycle and effect on ER-mediated transcription. Two patient-derived xenografts (PDX) modelling endocrine resistance were used to assess the efficacy of vistusertib, fulvestrant or the combination on tumour progression, and biomarker studies were conducted using immunohistochemistry and RNA-seq technologies.
    RESULTS: Vistusertib caused a dose-dependent decrease in proliferation of all the cell lines tested and reduced abundance of mTORC1, mTORC2 and cell cycle markers, but caused an increase in abundance of EGFR, IGF1R and ERBB3 in a context-dependent manner. ER-mediated transcription showed minimal effect of vistusertib. Combined therapy of vistusertib with fulvestrant showed synergy in two ER+ PDX models of resistance to endocrine therapy and delayed tumour progression after cessation of therapy.
    CONCLUSIONS: These data support the notion that models of acquired endocrine resistance may have a different sensitivity to mTOR inhibitor/endocrine therapy combinations.
    Keywords:  Breast cancer; Endocrine resistance; Oestrogen receptor; Vistusertib; mTORC1/2 signalling
  10. Skelet Muscle. 2019 Dec 02. 9(1): 30
      BACKGROUND: The mammalian target of rapamycin complex 2 (mTORC2), containing the essential protein rictor, regulates cellular metabolism and cytoskeletal organization by phosphorylating protein kinases, such as PKB/Akt, PKC, and SGK. Inactivation of mTORC2 signaling in adult skeletal muscle affects its metabolism, but not muscle morphology and function. However, the role of mTORC2 in adult muscle stem cells (MuSCs) has not been investigated.METHOD: Using histological, biochemical, and molecular biological methods, we characterized the muscle phenotype of mice depleted for rictor in the Myf5-lineage (RImyfKO) and of mice depleted for rictor in skeletal muscle fibers (RImKO). The proliferative and myogenic potential of MuSCs was analyzed upon cardiotoxin-induced injury in vivo and in isolated myofibers in vitro.
    RESULTS: Skeletal muscle of young and 14-month-old RImyfKO mice appeared normal in composition and function. MuSCs from young RImyfKO mice exhibited a similar capacity to proliferate, differentiate, and fuse as controls. In contrast, the number of MuSCs was lower in young RImyfKO mice than in controls after two consecutive rounds of cardiotoxin-induced muscle regeneration. Similarly, the number of MuSCs in RImyfKO mice decreased with age, which correlated with a decline in the regenerative capacity of mutant muscle. Interestingly, reduction in the number of MuSCs was also observed in 14-month-old RImKO muscle.
    CONCLUSIONS: Our study shows that mTORC2 signaling is dispensable for myofiber formation, but contributes to the homeostasis of MuSCs. Loss of mTORC2 does not affect their myogenic function, but impairs the replenishment of MuSCs after repeated injuries and their maintenance during aging. These results point to an important role of mTORC2 signaling in MuSC for muscle homeostasis.
    Keywords:  Muscle regeneration; Muscle stem cells; Rictor; mTORC2
  11. Dan Med J. 2019 Dec;pii: A5582. [Epub ahead of print]66(12):
      INTRODUCTION: Tuberous sclerosis complex (TSC) is a rare autosomal dominant multi-organ disease. In TSC, epilepsy is frequent and often treatment refractory. Dysfunction of the tumour-suppressing hamartin/tuberin complex leads to an over-activated mammalian target of rapamycin (mTOR) signalling pathway and uncontrolled cell growth. Protocolled treatment of TSC-associated epilepsy with the mTOR inhibitor everolimus has recently been approved by The Danish Medicines Council in Denmark.METHODS: Clinical data on the first Danish paediatric patients treated with everolimus for epilepsy and a review of the literature are presented.
    RESULTS: Four patients met the inclusion criteria and had been treated for more than 12 months. Onset of epilepsy was at a median age of 1.1 years (range: 0.3-3.3 years) and current age was 3.4 years (range: 2.2-7.4 years). The previous median number of antiepileptic drugs was 5.0 (range: 2-10) and the concomitant median number of antiepileptic drugs was 2.5 (range: 1-4). Several other treatment modalities had been or were still being applied, including ketogenic diet (n = 3), vagus nerve stimulation (n = 1) and epilepsy surgery (n = 2). The number of focal seizures was in the 20-160 range per week before everolimus. All patients had a > 50% seizure reduction after 12 months of everolimus treatment. One patient became seizure free. Side effects were mild and self-limiting.
    CONCLUSIONS: Early data on everolimus as an adjunctive treatment in TSC-associated epilepsy are promising with regards to both effect and tolerability.
    FUNDING: none.
    TRIAL REGISTRATION: not relevant.
  12. Acta Neuropathol Commun. 2019 Dec 03. 7(1): 191
      The contribution of mosaic alterations to tumors of the nervous system and to non-malignant neurological diseases has been unmasked thanks to the development of Next Generation Sequencing (NGS) technologies. We report here the case of a young patient without any remarkable familial medical history who was first referred at 7 years of age, for an autism spectrum disorder (ASD) of Asperger type, not associated with macrocephaly. The patient subsequently presented at 10 years of age with multiple nodular lesions located within the trigeminal, facial and acoustic nerve ganglia and at the L3 level. Histological examination of this latter lesion revealed a glioneuronal hamartoma, exhibiting heterogeneous PTEN immunoreactivity, astrocyte and endothelial cell nuclei expressing PTEN, but not ganglion cells. NGS performed on the hamartoma allowed the detection of a PTEN pathogenic variant in 30% of the reads. The presence of this variant in the DNA extracted from blood and buccal swabs in 3.5 and 11% of the NGS reads, respectively, confirmed the mosaic state of the PTEN variant. The anatomical distribution of the lesions suggests that the mutational event affecting PTEN occurred in neural crest progenitors, thus explaining the absence of macrocephaly. This report shows that mosaic alteration of PTEN may result in multiple central and peripheral nervous system hamartomas and that the presence of such alteration should be considered in patients with multiple nervous system masses, even in the absence of cardinal features of PTEN hamartoma tumor syndrome, especially macrocephaly.
    Keywords:  Central nervous system; Hamartomas; Mosaics; Neural crest derivatives; PTEN
  13. Cell Stem Cell. 2019 Dec 05. pii: S1934-5909(19)30426-6. [Epub ahead of print]25(6): 855-870.e11
      Medulloblastoma (MB), the most frequent malignant childhood brain tumor, can arise from cellular malfunctions during hindbrain development. Here we generate humanized models for Sonic Hedgehog (SHH)-subgroup MB via MYCN overexpression in primary human hindbrain-derived neuroepithelial stem (hbNES) cells or iPSC-derived NES cells, which display a range of aggressive phenotypes upon xenografting. iPSC-derived NES tumors develop quickly with leptomeningeal dissemination, whereas hbNES-derived cells exhibit delayed tumor formation with less dissemination. Methylation and expression profiling show that tumors from both origins recapitulate hallmarks of infant SHH MB and reveal that mTOR activation, as a result of increased Oct4, promotes aggressiveness of human SHH tumors. Targeting mTOR decreases cell viability and prolongs survival, showing the utility of these varied models for dissecting mechanisms mediating tumor aggression and demonstrating the value of humanized models for a better understanding of pediatric cancers.
    Keywords:  MYCN; POU5F1; mTOR; medulloblastoma; metastasis; neuroepithelial stem cells; reprogramming
  14. Biochim Biophys Acta Mol Cell Res. 2019 Nov 27. pii: S0167-4889(19)30224-1. [Epub ahead of print]1867(2): 118616
      Glycogen synthase kinase-3 (GSK-3) is a widely expressed serine/threonine kinase regulates a variety of cellular processes including proliferation, differentiation and death. Mammals harbor two structurally similar isoforms GSK-3α and β that have overlapping as well as unique functions. Of the two, GSK-3β has been studied (and reviewed) in far greater detail with analysis of GSK-3α often as an afterthought. It is now evident that systemic, chronic inhibition of either GSK-3β or both GSK-3α/β is not clinically feasible and if achieved would likely lead to adverse clinical conditions. Emerging evidence suggests important and specific roles for GSK-3α in fatty acid accumulation, insulin resistance, amyloid-β-protein precursor metabolism, atherosclerosis, cardiomyopathy, fibrosis, aging, fertility, and in a variety of cancers. Selective targeting of GSK-3α may present a novel therapeutic opportunity to alleviate a number of pathological conditions. In this review, we assess the evidence for roles of GSK-3α in a variety of pathophysiological settings.
    Keywords:  Aging; Atherosclerosis; Cancer; Cardiometabolic disorder; GSK-3alpha; Heart failure; Neurodegenerative disease
  15. Channels (Austin). 2019 Dec;13(1): 520-532
      PI 3-kinase α (PI3Kα) is a lipid kinase that converts phosphatidylinositol-4,5-bisphosphate (PIP2) to phosphatidylinositol-3,4,5-triphosphate (PIP3). PI3Kα regulates a variety of cellular processes such as nutrient sensing, cell cycle, migration, and others. Heightened activity of PI3Kα in many types of cancer made it a prime oncology drug target, but also raises concerns of possible adverse effects on the heart. Indeed, recent advances in preclinical models demonstrate an important role of PI3Kα in the control of cytoskeletal integrity, Na+ channel activity, cardioprotection, and prevention of arrhythmias.
    Keywords:  PI3Kα; arrhythmias; cytoskeleton; heart failure; late sodium current