bims-pideca Biomed News
on Class IA PI3K signalling in development and cancer
Issue of 2020‒06‒28
23 papers selected by
Ralitsa Radostinova Madsen
University College London Cancer Institute


  1. Sci Signal. 2020 Jun 23. pii: eaba8627. [Epub ahead of print]13(637):
    Hervieu A, Heuss SF, Zhang C, Barrow-McGee R, Joffre C, Ménard L, Clarke PA, Kermorgant S.
      Receptor tyrosine kinases (RTKs) are often overexpressed or mutated in cancers and drive tumor growth and metastasis. In the current model of RTK signaling, including that of MET, downstream phosphatidylinositol 3-kinase (PI3K) mediates both cell proliferation and cell migration, whereas the small guanosine triphosphatase (GTPase) Rac1 mediates cell migration. However, in cultured NIH3T3 and glioblastoma cells, we found that class I PI3K mediated oncogenic MET-induced cell migration but not anchorage-independent growth. In contrast, Rac1 regulated both processes in distinct ways. Downstream of PI3K, Rac1 mediated cell migration through its GTPase activity, whereas independently of PI3K, Rac1 mediated anchorage-independent growth in a GTPase-independent manner through an adaptor function. Through its RKR motif, Rac1 formed a complex with the kinase mTOR to promote its translocation to the plasma membrane, where its activity promoted anchorage-independent growth of the cell cultures. Inhibiting mTOR with rapamycin suppressed the growth of subcutaneous MET-mutant cell grafts in mice, including that of MET inhibitor-resistant cells. These findings reveal a GTPase-independent role for Rac1 in mediating a PI3K-independent MET-to-mTOR pathway and suggest alternative or combined strategies that might overcome resistance to RTK inhibitors in patients with cancer.
    DOI:  https://doi.org/10.1126/scisignal.aba8627
  2. J Cancer Res Clin Oncol. 2020 Jun 21.
    Kruger DT, Opdam M, van der Noort V, Sanders J, Nieuwenhuis M, de Valk B, Beelen KJ, Linn SC, Boven E.
      PURPOSE: Everolimus plus exemestane (EVE/EXE) is a registered treatment option for ER-positive, HER2-negative (ER +/HER2-) metastatic breast cancer (MBC), but resistance mechanisms limit efficacy. We aimed to find markers that might help select patients with a higher chance on benefit from EVE/EXE.METHODS: Immunohistochemistry (IHC) of PTEN, p-AKT(Thr308), p-AKT(Ser473), p-4EBP1, p-p70S6K, p-S6RP(Ser240/244), p-ERK1/2 and p-S6RP (Ser235/236) was performed on primary tumour tissue and on biopsies immediately taken from ER +/HER2- MBC patients before the start of standard EVE/EXE (Eudract 2013-004120-11). Unsupervised hierarchical clustering was executed to create heatmaps to distinguish subgroups of preferentially activated and less-activated PI3K/MAPK proteins. Uni- and multivariate Cox models were used for associations with PFS.
    RESULTS: Primary tumour tissue from 145 patients was retrieved. Median PFS was 5.4 months. Patients without (neo)adjuvant therapy (p = 0.03) or bone only disease (p = 0.04) had longer PFS on EVE/EXE. In primary tumours, neither single proteins nor PI3K/MAPK-associated heatmap subgroups were significantly associated with PFS. In 21 patients a non-osseous biopsy obtained before dosing was useful for continuous scoring, which demonstrated upregulation of several proteins as compared to readings in corresponding primary tumour tissues. These comparisons revealed that increased expression of p-4EBP1 was significantly associated with worse PFS (multivariate HR 3.69, p = 0.05).
    CONCLUSIONS: IHC of single proteins or heatmap subgroups of the differentially activated PI3K/MAPK pathways was not able to discriminate patients on EVE/EXE with poor or better PFS. Upregulation of p-4EBP1 in pre-treatment biopsies as compared to levels in primary tumours pointed towards shorter PFS.
    Keywords:  Breast cancer; Everolimus; Exemestane; Mitogen-activated protein kinase; Phosphatidylinositol-3-kinase; p-4EBP1
    DOI:  https://doi.org/10.1007/s00432-020-03291-x
  3. Hum Mol Genet. 2020 Jun 26. pii: ddaa118. [Epub ahead of print]
    Jaini R, Loya MG, King AT, Thacker S, Sarn NB, Yu Q, Stark GR, Eng C.
      Individuals with germline mutations in the gene encoding Phosphatase and Tensin Homolog on chromosome Ten (PTEN) are diagnosed with PTEN Tumor Hamartoma Syndrome (PHTS) and are at high risk for developing breast, thyroid and other cancers and/or autoimmunity or neurodevelopmental issues including autism spectrum disorders (ASD). Although well recognized as a tumor suppressor, involvement of PTEN mutations in mediating such a diverse range of phenotypes indicates a more central involvement for PTEN in immunity than previously recognized. To address this, sequencing of the T-cell receptor variable-region β-chain (TCRVB) was performed on peripheral blood from PHTS patients. Based on patient findings, we performed mechanistic studies in two Pten knock-in murine models, distinct from each other in cell compartment-specific predominance of Pten. We found that PTEN mutations in humans and mice are associated with a skewed T- and B-cell gene repertoire, characterized by increased prevalence of high frequency clones. Immunological characterization showed that Pten mutants have increased B-cell proliferation and a proclivity towards increased T-cell reactivity upon Toll-like-receptor stimulation. Furthermore, decreases in nuclear but not cytoplasmic Pten levels associated with a reduction in expression of the Autoimmune Regulator (Aire), a critical mediator of central immune tolerance. Mechanistically, we show that nuclear PTEN most likely regulates Aire expression via its emerging role in splicing regulation. We conclude that germline disruption of PTEN, both in human and mouse, results in compromised central immune tolerance processes that may significantly impact individual stress-responses and therefore predisposition to autoimmunity and cancer.
    DOI:  https://doi.org/10.1093/hmg/ddaa118
  4. Nat Metab. 2019 Nov;1(11): 1127-1140
    Wang C, Haas MA, Yang F, Yeo S, Okamoto T, Chen S, Wen J, Sarma P, Plas DR, Guan JL.
      Although mTORC1 negatively regulates autophagy in cultured cells, how autophagy impacts mTORC1 signaling, in particular in vivo, is less clear. Here we show that autophagy supports mTORC1 hyperactivation in NSCs lacking Tsc1, thereby promoting defects in NSC maintenance, differentiation, tumourigenesis, and the formation of the neurodevelopmental lesion of Tuberous Sclerosis Complex (TSC). Analysing mice that lack Tsc1 and the essential autophagy gene Fip200 in NSCs we find that TSC-deficient cells require autophagy to maintain mTORC1 hyperactivation under energy stress conditions, likely to provide lipids via lipophagy to serve as an alternative energy source for OXPHOS. In vivo, inhibition of lipophagy or its downstream catabolic pathway reverses defective phenotypes caused by Tsc1-null NSCs and reduces tumorigenesis in mouse models. These results reveal a cooperative function of selective autophagy in coupling energy availability with TSC pathogenesis and suggest a potential new therapeutic strategy to treat TSC patients.
    Keywords:  autophagy; energy stress; lipid catabolism; mTORC1; neural stem cells; tumorigenesis
    DOI:  https://doi.org/10.1038/s42255-019-0137-5
  5. Mol Cancer Res. 2020 Jun 25. pii: molcanres.0088.2020. [Epub ahead of print]
    Mohammad AH, Kim SH, Bertos N, El-Assaad W, Nandi I, Smith H, Yang J, Chen O, Gamache I, Rao T, Gagnon B, Gruosso T, Tremblay ML, Sonenberg N, Guiot MC, Muller W, Park M, Teodoro JG.
      PTEN loss-of-function contributes to hyperactivation of the phosphoinositide 3-kinase (PI3K) pathway and to drug resistance in breast cancer. Unchecked PI3K pathway signaling increases activation of the mechanistic target of rapamycin complex 1 (mTORC1), which promotes tumorigenicity. Several studies have suggested that vacuolar (H+)-ATPase (V-ATPase) complex activity is regulated by PI3K signaling. In this study, we showed that loss of PTEN elevated V-ATPase activity. Enhanced V-ATPase activity was mediated by increased expression of the ATPase H+ Transporting Accessory Protein 2 (ATP6AP2), also known as the Prorenin Receptor (PRR). PRR is cleaved into a secreted extracellular fragment (sPRR) and an intracellular fragment (M8.9) that remains associated with the V-ATPase complex. Reduced PTEN expression increased V-ATPase complex activity in a PRR-dependent manner. Breast cancer cell lines with reduced PTEN expression demonstrated increased PRR expression. Similarly, PRR expression became elevated upon PTEN deletion in a mouse model of breast cancer. Interestingly, concentration of sPRR was elevated in the plasma of breast cancer patients and correlated with tumor burden in HER2-enriched cancers. Moreover, PRR was essential for proper HER2 receptor expression, localization and signaling. PRR knockdown attenuated HER2 signaling and resulted in reduced Akt and ERK 1/2 phosphorylation, and in lower mTORC1 activity. Overall, our study demonstrates a mechanism by which PTEN loss in breast cancer can potentiate multiple signaling pathways through upregulation of the V-ATPase complex. Implications: Our study contributed to the understanding of the role of the V-ATPase complex in breast cancer cell tumorigenesis and provided a potential biomarker in breast cancer.
    DOI:  https://doi.org/10.1158/1541-7786.MCR-20-0088
  6. Cell Rep. 2020 Jun 23. pii: S2211-1247(20)30760-9. [Epub ahead of print]31(12): 107780
    Di Nardo A, Lenoël I, Winden KD, Rühmkorf A, Modi ME, Barrett L, Ercan-Herbst E, Venugopal P, Behne R, Lopes CAM, Kleiman RJ, Bettencourt-Dias M, Sahin M.
      Tuberous sclerosis complex (TSC) is a neurogenetic disorder that leads to elevated mechanistic targeting of rapamycin complex 1 (mTORC1) activity. Cilia can be affected by mTORC1 signaling, and ciliary deficits are associated with neurodevelopmental disorders. Here, we examine whether neuronal cilia are affected in TSC. We show that cortical tubers from TSC patients and mutant mouse brains have fewer cilia. Using high-content image-based assays, we demonstrate that mTORC1 activity inversely correlates with ciliation in TSC1/2-deficient neurons. To investigate the mechanistic relationship between mTORC1 and cilia, we perform a phenotypic screen for mTORC1 inhibitors with TSC1/2-deficient neurons. We identify inhibitors of the heat shock protein 90 (Hsp90) that suppress mTORC1 through regulation of phosphatidylinositol 3-kinase (PI3K)/Akt signaling. Pharmacological inhibition of Hsp90 rescues ciliation through downregulation of Hsp27. Our study uncovers the heat-shock machinery as a druggable signaling node to restore mTORC1 activity and cilia due to loss of TSC1/2, and it provides broadly applicable platforms for studying TSC-related neuronal dysfunction.
    Keywords:  17-AGG; Hsp27; Hsp90; TSC; autism; brain; cilia; ciliopathy; mTOR
    DOI:  https://doi.org/10.1016/j.celrep.2020.107780
  7. Hum Mol Genet. 2020 Jun 26. pii: ddaa121. [Epub ahead of print]
    Kapfhamer D, McKenna J, Yoon CJ, Murray-Stewart T, Casero RA, Gambello MJ.
      Tuberous sclerosis complex (TSC) is a rare autosomal dominant neurodevelopmental disorder characterized by variable expressivity. TSC results from inactivating variants within the TSC1 or TSC2 genes, leading to constitutive activation of mechanistic Target of Rapamycin Complex 1 (mTORC1) signaling. Using a mouse model of TSC (Tsc2-RG) in which the Tsc2 gene is deleted in radial glial precursors and their neuronal and glial descendants, we observed increased ornithine decarboxylase (ODC) enzymatic activity and concentration of its product, putrescine. To test if increased ODC activity and dysregulated polyamine metabolism contributes to the neurodevelopmental defects of Tsc2-RG mice, we used pharmacologic and genetic approaches to reduce ODC activity in Tsc2-RG mice, followed by histologic assessment of brain development. We observed that decreasing ODC activity and putrescine levels in Tsc2-RG mice worsened many of the neurodevelopmental phenotypes, including brain growth and neuronal migration defects, astrogliosis and oxidative stress. These data suggest a protective effect of increased ODC activity and elevated putrescine that modify the phenotype in this developmental Tsc2-RG model.
    DOI:  https://doi.org/10.1093/hmg/ddaa121
  8. Cell Rep. 2020 Jun 23. pii: S2211-1247(20)30787-7. [Epub ahead of print]31(12): 107806
    Triki M, Rinaldi G, Planque M, Broekaert D, Winkelkotte AM, Maier CR, Janaki Raman S, Vandekeere A, Van Elsen J, Orth MF, Grünewald TGP, Schulze A, Fendt SM.
      Cancer cells display an increased plasticity in their lipid metabolism, which includes the conversion of palmitate to sapienate via the enzyme fatty acid desaturase 2 (FADS2). We find that FADS2 expression correlates with mammalian target of rapamycin (mTOR) signaling and sterol regulatory element-binding protein 1 (SREBP-1) activity across multiple cancer types and is prognostic in some cancer types. Accordingly, activating mTOR signaling by deleting tuberous sclerosis complex 2 (Tsc2) or overexpression of SREBP-1/2 is sufficient to increase FADS2 mRNA expression and sapienate metabolism in mouse embryonic fibroblasts (MEFs) and U87 glioblastoma cells, respectively. Conversely, inhibiting mTOR signaling decreases FADS2 expression and sapienate biosynthesis in MEFs with Tsc2 deletion, HUH7 hepatocellular carcinoma cells, and orthotopic HUH7 liver xenografts. In conclusion, we show that mTOR signaling and SREBP activity are sufficient to activate sapienate metabolism by increasing FADS2 expression. Consequently, targeting mTOR signaling can reduce sapienate metabolism in vivo.
    Keywords:  FADS2; SCD1; SREBP; cancer; fatty acid metabolism; glioblastoma; hepatocellular carcinoma; mTOR; palmitate; palmitoleate; sapienate
    DOI:  https://doi.org/10.1016/j.celrep.2020.107806
  9. Hum Mol Genet. 2020 Jun 22. pii: ddaa127. [Epub ahead of print]
    Yehia L, Eng C.
      Hereditary cancer syndromes represent ~10% of all incident cancers. It is important to identify individuals having these disorders because, unlike patients with sporadic cancer, these patients require specialised life-long care, with implications for their families. Importantly, the identification of alterations in cancer-predisposing genes facilitates gene-informed molecular diagnosis, cancer risk assessment and gene-specific clinical management. Moreover, knowledge about gene function in the inherited cancers offers insights towards biological processes pertinent to the more common sporadic cancers. Conversely, without a known gene, clinical management is less precise and it is impossible to offer predictive testing of family members. PTEN hamartoma tumour syndrome (PHTS) is an umbrella term encompassing four overgrowth and cancer predisposition disorders associated with germline PTEN mutations. With time, it became evident that only a finite subset of individuals with PHTS-associated phenotypes harbour germline PTEN mutations. Therefore, non-PTEN aetiologies exist in PTEN wildtype patients. Indeed, gene discovery efforts over the last decade elucidated multiple candidate cancer predisposition genes. While a subset of genes (e.g. AKT1, PIK3CA) are biologically plausible as being key effectors within the PTEN signalling cascade, other genes required meticulous functional interrogation to explain their contribution to PHTS-related phenotypes. Collectively, the extensive phenotypic heterogeneity of the clinical syndromes typically united by PTEN is reflected by the genetic heterogeneity revealed through gene discovery. Validating these gene discoveries is critical because while PTEN wildtype patients can be diagnosed clinically, they do not have the benefit of specific gene-informed risk assessment and subsequent management.
    DOI:  https://doi.org/10.1093/hmg/ddaa127
  10. Nat Commun. 2020 Jun 26. 11(1): 3257
    Voskuil FJ, Steinkamp PJ, Zhao T, van der Vegt B, Koller M, Doff JJ, Jayalakshmi Y, Hartung JP, Gao J, Sumer BD, Witjes MJH, van Dam GM, .
      Cancer cell metabolism leads to a uniquely acidic microenvironment in solid tumors, but exploiting the labile extracellular pH differences between cancer and normal tissues for clinical use has been challenging. Here we describe the clinical translation of ONM-100, a nanoparticle-based fluorescent imaging agent. This is comprised of an ultra-pH sensitive amphiphilic polymer, conjugated with indocyanine green, which rapidly and irreversibly dissociates to fluoresce in the acidic extracellular tumor microenvironment due to the mechanism of nanoscale macromolecular cooperativity. Primary outcomes were safety, pharmacokinetics and imaging feasilibity of ONM-100. Secondary outcomes were to determine a range of safe doses of ONM-100 for intra-operative imaging using commonly used fluorescence camera systems. In this study (Netherlands National Trial Register #7085), we report that ONM-100 was well tolerated, and four solid tumor types could be visualized both in- and ex vivo in thirty subjects. ONM-100 enables detection of tumor-positive resection margins in 9/9 subjects and four additional otherwise missed occult lesions. Consequently, this pH-activatable optical imaging agent may be clinically beneficial in differentiating previously unexploitable narrow physiologic differences.
    DOI:  https://doi.org/10.1038/s41467-020-16814-4
  11. Neuropharmacology. 2020 Jun 20. pii: S0028-3908(20)30224-0. [Epub ahead of print] 108156
    Vieira de Assis Lima I, Quaglio Bellozi PM, Batista EM, Vilela LR, Brandão IL, Ribeiro FM, Dutra Moraes MF, Moreira FA, Pinheiro de Oliveira AC.
      The phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB/Akt)/mechanistic target of rapamycin (mTOR) signaling pathway has been associated with several pathologies in the central nervous system (CNS), including epilepsy. There is evidence supporting the hypothesis that the PI3Kγ signaling pathway may mediate the powerful anticonvulsant properties associated with the cannabinoidergic system. This work aims to investigate if the anticonvulsant and neuroprotective effects of cannabidiol (CBD) are mediated by PI3Kγ. In vitro and in vivo experiments were performed on C57Bl/6 wild-type (WT) and PI3Kγ-/- mice. Behavioral seizures were induced by bilateral intra-hippocampal pilocarpine microinjection. Twenty-four hours after the first behavioral seizure, animals were perfused and their brains removed and processed, for histological analysis of neurodegeneration, microgliosis and astrocytosis. Primary cultures of hippocampal neurons were used for glutamate-induced cell death assay. CDB increased latency and reduced the severity of pilocarpine-induced behavioral seizures, as well as prevented postictal changes, such as neurodegeneration, microgliosis and astrocytosis, in WT animals, but not in PI3Kγ-/-. CBD in vivo effects were abolished by pharmacological inhibition of cannabinoid receptor or mTOR. In vitro, PI3Kγ inhibition or deficiency also changed CBD protection observed in glutamate-induced cell death assay. Thus, we suggest that the modulation of PI3K/mTOR signaling pathway is involved in the anticonvulsant and neuroprotective effects of CBD. These findings are important not only for the elucidation of the mechanisms of action of CBD, which are currently poorly understood, but also to allow the prediction of therapeutic and side effects, ensuring efficacy and safety in the treatment of patients with epilepsy.
    Keywords:  Cannabidiol; Epilepsy; Excitotoxicity; Mechanistic target of rapamycin; Phosphatidylinositol 3-kinase; Seizures
    DOI:  https://doi.org/10.1016/j.neuropharm.2020.108156
  12. Oncogene. 2020 Jun 21.
    Nollet EA, Cardo-Vila M, Ganguly SS, Tran JD, Schulz VV, Cress A, Corey E, Miranti CK.
      The androgen receptor (AR) is the major driver of prostate cancer growth and survival. However, almost all patients relapse with castration-resistant disease (CRPC) when treated with anti-androgen therapy. In CRPC, AR is often aberrantly activated independent of androgen. Targeting survival pathways downstream of AR could be a viable strategy to overcome CRPC. Surprisingly, little is known about how AR drives prostate cancer survival. Furthermore, CRPC tumors in which Pten is lost are also resistant to eradication by PI3K inhibitors. We sought to identify the mechanism by which AR drives tumor survival in CRPC to identify ways to overcome resistance to PI3K inhibition. We found that integrins α6β1 and Bnip3 are selectively elevated in CRPC downstream of AR. While integrin α6 promotes survival and is a direct transcriptional target of AR, the ability of AR to induce Bnip3 is dependent on adhesion to laminin and integrin α6β1-dependent nuclear translocation of HIF1α. Integrins α6β1 and Bnip3 were found to promote survival of CRPC cells selectively on laminin through the induction of autophagy and mitophagy. Furthermore, blocking Bnip3 or integrin α6β1 restored sensitivity to PI3K inhibitors in Pten-negative CRPC. We identified an AR driven pathway that cooperates with laminin and hypoxia to drive resistance to PI3K inhibitors. These findings can help explain in part why PI3K inhibitors have failed in clinical trials to overcome AR-dependent CRPC.
    DOI:  https://doi.org/10.1038/s41388-020-1370-9
  13. Adipocyte. 2020 Dec;9(1): 290-301
    Kässner F, Kirstein A, Händel N, Schmid GL, Landgraf K, Berthold A, Tannert A, Schaefer M, Wabitsch M, Kiess W, Körner A, Garten A.
      Few human cell strains are suitable and readily available as in vitro adipocyte models. We used resected lipoma tissue from a patient with germline phosphatase and tensin homolog (PTEN) haploinsufficiency to establish a preadipocyte cell strain termed LipPD1 and aimed to characterize cellular functions and signalling pathway alterations in comparison to the established adipocyte model Simpson-Golabi-Behmel-Syndrome (SGBS) and to primary stromal-vascular fraction cells. We found that both cellular life span and the capacity for adipocyte differentiation as well as adipocyte-specific functions were preserved in LipPD1 and comparable to SGBS adipocytes. Basal and growth factor-stimulated activation of the PI3 K/AKT signalling pathway was increased in LipPD1 preadipocytes, corresponding to reduced PTEN levels in comparison to SGBS cells. Altogether, LipPD1 cells are a novel primary cell model with a defined genetic lesion suitable for the study of adipocyte biology.
    Keywords:  3D culture; AKT; Lipoma; SGBS; adipocyte differentiation; cellular life-span; phosphatases; phosphoinositide-3-kinase
    DOI:  https://doi.org/10.1080/21623945.2020.1785083
  14. Front Nutr. 2020 ;7 81
    Venniyoor A.
      The modern obesity epidemic with associated disorders of metabolism and cancer has been attributed to the presence of "thrifty genes". In the distant past, these genes helped the organism to improve energy efficiency and store excess energy safely as fat to survive periods of famine, but in the present day obesogenic environment, have turned detrimental. I propose PTEN as the likely gene as it has functions that span metabolism, cancer and reproduction, all of which are deranged in obesity and insulin resistance. The activity of PTEN can be calibrated in utero by availability of nutrients by the methylation arm of the epigenetic pathway. Deficiency of protein and choline has been shown to upregulate DNA methyltransferases (DNMT), especially 1 and 3a; these can then methylate promoter region of PTEN and suppress its expression. Thus, the gene is tuned like a metabolic rheostat proportional to the availability of specific nutrients, and the resultant "dose" of the protein, which sits astride and negatively regulates the insulin-PI3K/AKT/mTOR pathway, decides energy usage and proliferation. This "fixes" the metabolic capacity of the organism periconceptionally to a specific postnatal level of nutrition, but when faced with a discordant environment, leads to obesity related diseases.
    Keywords:  NAFLD; PTEN (phosphatase and tensin homolog deleted on chromosome 10); carcinogenesis; diabetes mellitus; insulin resistance; polycystic ovarian disease (PCOD); thrifty gene hypothesis
    DOI:  https://doi.org/10.3389/fnut.2020.00081
  15. Nat Commun. 2020 Jun 24. 11(1): 3200
    Bonucci M, Kuperwasser N, Barbe S, Koka V, de Villeneuve D, Zhang C, Srivastava N, Jia X, Stokes MP, Bienaimé F, Verkarre V, Lopez JB, Jaulin F, Pontoglio M, Terzi F, Delaval B, Piel M, Pende M.
      mTOR activation is essential and sufficient to cause polycystic kidneys in Tuberous Sclerosis Complex (TSC) and other genetic disorders. In disease models, a sharp increase of proliferation and cyst formation correlates with a dramatic loss of oriented cell division (OCD). We find that OCD distortion is intrinsically due to S6 kinase 1 (S6K1) activation. The concomitant loss of S6K1 in Tsc1-mutant mice restores OCD but does not decrease hyperproliferation, leading to non-cystic harmonious hyper growth of kidneys. Mass spectrometry-based phosphoproteomics for S6K1 substrates revealed Afadin, a known component of cell-cell junctions required to couple intercellular adhesions and cortical cues to spindle orientation. Afadin is directly phosphorylated by S6K1 and abnormally decorates the apical surface of Tsc1-mutant cells with E-cadherin and α-catenin. Our data reveal that S6K1 hyperactivity alters centrosome positioning in mitotic cells, affecting oriented cell division and promoting kidney cysts in conditions of mTOR hyperactivity.
    DOI:  https://doi.org/10.1038/s41467-020-16978-z
  16. Cell Rep. 2020 Jun 23. pii: S2211-1247(20)30775-0. [Epub ahead of print]31(12): 107794
    Tang R, Jiang Z, Chen F, Yu W, Fan K, Tan J, Zhang Z, Liu X, Li P, Yuan K.
      As a core component of the mitotic checkpoint complex, BubR1 has a modular organization of molecular functions, with KEN box and other motifs at the N terminus inhibiting the anaphase-promoting complex/cyclosome, and a kinase domain at the C terminus, whose function remains unsettled, especially at organismal levels. We generate knock-in BubR1 mutations in the Drosophila genome to separately disrupt the KEN box and the kinase domain. All of the mutants are homozygously viable and fertile and show no defects in mitotic progression. The mutants without kinase activity have an increased lifespan and phenotypic changes associated with attenuated insulin signaling, including reduced InR on the cell membrane, weakened PI3K and AKT activity, and elevated expression of dFoxO targets. The BubR1 kinase-dead mutants have a reduced cap cell number in female germaria, which can be rescued by expressing a constitutively active InR. We conclude that one major physiological role of BubR1 kinase in Drosophila is to modulate insulin signaling.
    Keywords:  BubR1; Drosophila; cap cell; enteroendocrine cell; germarium; insulin signaling; intestinal stem cell; mitosis; spindle assembly checkpoint
    DOI:  https://doi.org/10.1016/j.celrep.2020.107794
  17. Nature. 2020 Jun 24.
    Oginuma M, Harima Y, Tarazona OA, Diaz-Cuadros M, Michaut A, Ishitani T, Xiong F, Pourquié O.
      Formation of the body of vertebrate embryos proceeds sequentially by posterior addition of tissues from the tail bud. Cells of the tail bud and the posterior presomitic mesoderm, which control posterior elongation1, exhibit a high level of aerobic glycolysis that is reminiscent of the metabolic status of cancer cells experiencing the Warburg effect2,3. Glycolytic activity downstream of fibroblast growth factor controls WNT signalling in the tail bud3. In the neuromesodermal precursors of the tail bud4, WNT signalling promotes the mesodermal fate that is required for sustained axial elongation, at the expense of the neural fate3,5. How glycolysis regulates WNT signalling in the tail bud is currently unknown. Here we used chicken embryos and human tail bud-like cells differentiated in vitro from induced pluripotent stem cells to show that these cells exhibit an inverted pH gradient, with the extracellular pH lower than the intracellular pH, as observed in cancer cells6. Our data suggest that glycolysis increases extrusion of lactate coupled to protons via the monocarboxylate symporters. This contributes to elevating the intracellular pH in these cells, which creates a favourable chemical environment for non-enzymatic β-catenin acetylation downstream of WNT signalling. As acetylated β-catenin promotes mesodermal rather than neural fate7, this ultimately leads to activation of mesodermal transcriptional WNT targets and specification of the paraxial mesoderm in tail bud precursors. Our work supports the notion that some tumour cells reactivate a developmental metabolic programme.
    DOI:  https://doi.org/10.1038/s41586-020-2428-0
  18. Cell Death Discov. 2020 ;6 52
    Fang Y, Li F, Qi C, Mao X, Wang F, Zhao Z, Chen JK, Zhang Z, Wu H.
      Tuberous sclerosis complex (TSC) is characterized by hamartomatous lesions in multiple organs, with most patients developing polycystic kidney disease and leading to a decline of renal function. TSC is caused by loss-of-function mutations in either Tsc1 or Tsc2 gene, but currently, there is no effective treatment for aberrant kidney growth in TSC patients. By generating a renal proximal tubule-specific Tsc1 gene-knockout (Tsc1 ptKO) mouse model, we observed that Tsc1 ptKO mice developed aberrantly enlarged kidneys primarily due to hypertrophy and proliferation of proximal tubule cells, along with some cystogenesis, interstitial inflammation, and fibrosis. Mechanistic studies revealed inhibition of AMP-activated protein kinase (AMPK) phosphorylation at Thr-172 and activation of Akt phosphorylation at Ser-473 and Thr-308. We therefore treated Tsc1 ptKO mice with the AMPK activator, metformin, by daily intraperitoneal injection. Our results indicated that metformin increased the AMPK phosphorylation, but decreased the Akt phosphorylation. These signaling modulations resulted in inhibition of proliferation and induction of apoptosis in the renal proximal tubule cells of Tsc1 ptKO mice. Importantly, metformin treatment effectively prevented aberrant kidney enlargement and cyst growth, inhibited inflammatory response, attenuated interstitial fibrosis, and protected renal function. The effects of metformin were further confirmed by in vitro experiments. In conclusion, this study indicates a potential therapeutic effect of metformin on Tsc1 deletion-induced kidney pathology, although currently metformin is primarily prescribed to treat patients with type 2 diabetes.
    Keywords:  Experimental models of disease; Polycystic kidney disease
    DOI:  https://doi.org/10.1038/s41420-020-0285-0
  19. Nat Rev Mol Cell Biol. 2020 Jun 23.
    Lavoie H, Gagnon J, Therrien M.
      The proteins extracellular signal-regulated kinase 1 (ERK1) and ERK2 are the downstream components of a phosphorelay pathway that conveys growth and mitogenic signals largely channelled by the small RAS GTPases. By phosphorylating widely diverse substrates, ERK proteins govern a variety of evolutionarily conserved cellular processes in metazoans, the dysregulation of which contributes to the cause of distinct human diseases. The mechanisms underlying the regulation of ERK1 and ERK2, their mode of action and their impact on the development and homeostasis of various organisms have been the focus of much attention for nearly three decades. In this Review, we discuss the current understanding of this important class of kinases. We begin with a brief overview of the structure, regulation, substrate recognition and subcellular localization of ERK1 and ERK2. We then systematically discuss how ERK signalling regulates six fundamental cellular processes in response to extracellular cues. These processes are cell proliferation, cell survival, cell growth, cell metabolism, cell migration and cell differentiation.
    DOI:  https://doi.org/10.1038/s41580-020-0255-7
  20. FASEB J. 2020 Jun 22.
    Ruiz CF, Montal ED, Haley JA, Bott AJ, Haley JD.
      Cancer cells require extensive metabolic reprograming in order to provide the bioenergetics and macromolecular precursors needed to sustain a malignant phenotype. Mutant KRAS is a driver oncogene that is well-known for its ability to regulate the ERK and PI3K signaling pathways. However, it is now appreciated that KRAS can promote the tumor growth via upregulation of anabolic metabolism. We recently reported that oncogenic KRAS promotes a gene expression program of de novo lipogenesis in non-small cell lung cancer (NSCLC). To define the mechanism(s) responsible, we focused on the lipogenic transcription factor SREBP1. We observed that KRAS increases SREBP1 expression and genetic knockdown of SREBP1 significantly inhibited the cell proliferation of mutant KRAS-expressing cells. Unexpectedly, lipogenesis was not significantly altered in cells subject to SREBP1 knockdown. Carbon tracing metabolic studies showed a significant decrease in oxidative phosphorylation and RNA-seq data revealed a significant decrease in mitochondrial encoded subunits of the electron transport chain (ETC). Taken together, these data support a novel role, distinct from lipogenesis, of SREBP1 on mitochondrial function in mutant KRAS NSCLC.
    Keywords:  cancer metabolism; de novo lipogenesis; electron transport chain; oxidative phosphorylation
    DOI:  https://doi.org/10.1096/fj.202000052R
  21. J Biol Chem. 2020 Jun 22. pii: jbc.RA120.013678. [Epub ahead of print]
    Haizel SA, Bhardwaj U, Gonzalez RL, Mitra S, Goss DJ.
      During unfavorable conditions (e.g. tumor hypoxia or viral infection), canonical, cap-dependent mRNA translation is suppressed in human cells. Nonetheless, a subset of physiologically important mRNAs (e.g. hypoxia-inducible factor 1α [HIF-1α], fibroblast growth factor 9 [FGF-9], and p53) is still translated by an unknown, cap-independent mechanism. Additionally, expression levels of eukaryotic translation initiation factor 4 gamma I (eIF4GI) and of its homolog, death-associated protein 5 (DAP5), are elevated. By examining the 5' UTRs of HIF-1α, FGF-9, and p53 mRNAs and using fluorescence anisotropy binding studies, luciferase reporter-based in vitro translation assays, and mutational analyses, we demonstrate here that eIF4GI and DAP5 specifically bind to the 5' UTRs of these cap-independently translated mRNAs. Surprisingly, we found that the eIF4E-binding domain of eIF4GI increases not only the binding affinity, but also the selectivity among these mRNAs. We further demonstrate that the affinities of eIF4GI and DAP5 binding to these 5' UTRs correlate with the efficiency with which these factors drive cap-independent translation of these mRNAs. Integrating the results of our binding and translation assays, we conclude that eIF4GI or DAP5 is critical for recruitment of a specific subset of mRNAs to the ribosome, providing mechanistic insight into their cap-independent translation.
    Keywords:  Cap-independent translation; Death Associated Protein 5 DAP5; cell stress; eukaryotic translation initiation factor 4G (eIF4G); fluorescence anisotropy; gene regulation; hypoxia-inducible factor (HIF); mRNA; protein synthesis; protein-nucleic acid interaction
    DOI:  https://doi.org/10.1074/jbc.RA120.013678
  22. Oncogene. 2020 Jun 24.
    Lundberg A, Lindström LS, Parker JS, Löverli E, Perou CM, Bergh J, Tobin NP.
      Pan-cancer genomic analyses based on the magnitude of pathway activity are currently lacking. Focusing on the cell cycle, we examined the DNA mutations and chromosome arm-level aneuploidy within tumours with low, intermediate and high cell-cycle activity in 9515 pan-cancer patients with 32 different tumour types. Boxplots showed that cell-cycle activity varied broadly across and within all cancers. TP53 and PIK3CA mutations were common in all cell cycle score (CCS) tertiles but with increasing frequency as cell-cycle activity levels increased (P < 0.001). Mutations in BRAF and gains in 16p were less frequent in CCS High tumours (P < 0.001). In Kaplan-Meier analysis, patients whose tumours were CCS Low had a longer Progression Free Interval (PFI) relative to Intermediate or High (P < 0.001) and this significance remained in multivariable analysis (CCS Intermediate: HR = 1.37; 95% CI 1.17-1.60, CCS High: 1.54; 1.29-1.84, CCS Low = Ref). These results demonstrate that whilst similar DNA alterations can be found at all cell-cycle activity levels, some notable exceptions exist. Moreover, independent prognostic information can be derived on a pan-cancer level from a simple measure of cell-cycle activity.
    DOI:  https://doi.org/10.1038/s41388-020-1367-4
  23. Hematol Oncol Clin North Am. 2020 Aug;pii: S0889-8588(20)30033-2. [Epub ahead of print]34(4): 727-741
    Lynch RC, Gopal AK.
      Chemoimmunotherapy is the standard frontline treatment for symptomatic or high tumor burden follicular lymphoma. Better understanding of the molecular mechanisms of lymphomagenesis has led to the development of drugs targeting these pathways. The phosphatidylinositol-3-kinase pathway is an important signaling pathway in B-cell lymphomas. Three drugs in this class have received FDA approval. We describe the efficacy and toxicities of phosphatidylinositol-3-kinase inhibitors. Response rates in highly refractory disease are high, demonstrate few long-term remissions, and have high long-term toxicity. Early data on dosing and combination strategies are promising and may change how we use these agents in the coming years.
    Keywords:  Autoimmune toxicity; Combination therapy; Follicular lymphoma; PI3 kinase; Targeted therapy
    DOI:  https://doi.org/10.1016/j.hoc.2020.02.008