bims-pideca Biomed News
on Class IA PI3K signalling in development and cancer
Issue of 2020‒05‒17
sixteen papers selected by
Ralitsa Radostinova Madsen
University College London Cancer Institute


  1. J Immunol. 2020 May 15. pii: ji2000043. [Epub ahead of print]
    Stark AK, Davenport ECM, Patton DT, Scudamore CL, Vanhaesebroeck B, Veldhoen M, Garden OA, Okkenhaug K.
      Class I PI3K enzymes are critical for the maintenance of effective immunity. In T cells, PI3Kα and PI3Kδ are activated by the TCR and costimulatory receptors, whereas PI3Kγ is activated by G protein-coupled chemokine receptors. PI3Kδ is a key regulator of regulatory T (Treg) cell function. PI3K isoform-selective inhibitors are in development for the treatment of diseases associated with immune dysregulation, including chronic inflammatory conditions, cancer, and autoimmune diseases. Idelalisib (PI3Kδ), alpelisib (PI3Kα), duvelisib (PI3Kδ/γ), and copanlisib (pan-PI3K) have recently been approved for use in cancer treatment. Although effective, these therapies often have severe side effects associated with immune dysregulation and, in particular, loss of Treg cells. Therefore, it is important to gain a better understanding of the relative contribution of different PI3K isoforms under homeostatic and inflammatory conditions. Experimental autoimmune encephalitis is a mouse model of T cell-driven CNS inflammation, in which Treg cells play a key protective role. In this study, we show that PI3Kδ is required to maintain normal Treg cell development and phenotype under homeostatic conditions but that loss of PI3Kδ alone in Treg cells does not lead to autoimmunity. However, combined loss of PI3Kα and PI3Kδ signaling resulted in increased experimental autoimmune encephalitis disease severity. Moreover, mice lacking PI3Kα and PI3Kδ in Treg cells developed spontaneous peripheral nerve inflammation. These results show a key role for PI3K signaling in Treg cell-mediated protection against CNS inflammation.
    DOI:  https://doi.org/10.4049/jimmunol.2000043
  2. Proc Natl Acad Sci U S A. 2020 May 11. pii: 201921015. [Epub ahead of print]
    Hosooka T, Hosokawa Y, Matsugi K, Shinohara M, Senga Y, Tamori Y, Aoki C, Matsui S, Sasaki T, Kitamura T, Kuroda M, Sakaue H, Nomura K, Yoshino K, Nabatame Y, Itoh Y, Yamaguchi K, Hayashi Y, Nakae J, Accili D, Yokomizo T, Seino S, Kasuga M, Ogawa W.
      Although adipocytes are major targets of insulin, the influence of impaired insulin action in adipocytes on metabolic homeostasis remains unclear. We here show that adipocyte-specific PDK1 (3'-phosphoinositide-dependent kinase 1)-deficient (A-PDK1KO) mice manifest impaired metabolic actions of insulin in adipose tissue and reduction of adipose tissue mass. A-PDK1KO mice developed insulin resistance, glucose intolerance, and hepatic steatosis, and this phenotype was suppressed by additional ablation of FoxO1 specifically in adipocytes (A-PDK1/FoxO1KO mice) without an effect on adipose tissue mass. Neither circulating levels of adiponectin and leptin nor inflammatory markers in adipose tissue differed between A-PDK1KO and A-PDK1/FoxO1KO mice. Lipidomics and microarray analyses revealed that leukotriene B4 (LTB4) levels in plasma and in adipose tissue as well as the expression of 5-lipoxygenase (5-LO) in adipose tissue were increased and restored in A-PDK1KO mice and A-PDK1/FoxO1KO mice, respectively. Genetic deletion of the LTB4 receptor BLT1 as well as pharmacological intervention to 5-LO or BLT1 ameliorated insulin resistance in A-PDK1KO mice. Furthermore, insulin was found to inhibit LTB4 production through down-regulation of 5-LO expression via the PDK1-FoxO1 pathway in isolated adipocytes. Our results indicate that insulin signaling in adipocytes negatively regulates the production of LTB4 via the PDK1-FoxO1 pathway and thereby maintains systemic insulin sensitivity.
    Keywords:  5-lipoxygenase; FoxO1; PDK1; insulin resistance; leukotriene B4
    DOI:  https://doi.org/10.1073/pnas.1921015117
  3. Breast Cancer Res. 2020 May 13. 22(1): 45
    Martínez-Sáez O, Chic N, Pascual T, Adamo B, Vidal M, González-Farré B, Sanfeliu E, Schettini F, Conte B, Brasó-Maristany F, Rodríguez A, Martínez D, Galván P, Rodríguez AB, Martinez A, Muñoz M, Prat A.
      PURPOSE: The therascreen PIK3CA mutation assay and the alpha-specific PI3K inhibitor alpelisib are FDA-approved for identifying and treating patients with advanced PIK3CA-mutated (PIK3CAmut) breast cancer (BC). However, it is currently unknown to what extend this assay detects most PIK3CA mutations in BC. This information is critical as patients and clinicians are using this and other genomic assays to indicate alpelisib.METHODS: Data from 6338 patients with BC was explored across 10 publicly available studies. The primary objective was to evaluate the proportion and distribution of PIK3CA mutations in BC. Secondary objectives were (1) to evaluate in silico the spectrum of PIK3CA mutations in BC that would be captured by the therascreen panel; (2) to evaluate the proportion and distribution of PIK3CA mutations in hormone receptor-positive/HER2-negative (HR+/HER2-), HER2+, and triple-negative BC (TNBC); and (3) to explore the identification of PIK3CA mutations in a cohort of 48 HR+/HER2- advanced BC patients by the Guardant B360 circulating tumor DNA (ctDNA) assay.
    RESULTS: Patients with PIK3CAmut tumors represented 35.7% (2261/6338). Five PIK3CA mutations comprised 73% of all PIK3CA mutations: H1047R (35%), E545K (17%), E542K (11%), N345K (6%), and H1047L (4%). Therascreen gene list would capture 72% of all PIK3CA mutations and 80% of patients with a known PIK3CAmut BC. Among patients with double PIK3CAmut tumors (12% of all PIK3CAmut), the therascreen panel would capture 78% as harboring 1 single PIK3CA mutation, 17% as PIK3CAmut undetected, and 5% as PIK3CA double-mut. PIK3CA mutation rates were lower in TNBC (16%) compared to HR+/HER2 (42%) and HER2+ (31%) BC; however, the distribution of the 4 main PIK3CA mutations across subtypes was similar. Finally, 28% of PIK3CA mutations identified in ctDNA in 48 patients with advanced HR+/HER2- BC were not part of the therascreen panel.
    CONCLUSION: PIK3CA mutations in BC are heterogenous and ~ 20% of patients with a known PIK3CA mutation, and 95% with a known double PIK3CAmut tumor, would not be captured by the therascreen panel. Finally, the clinical utility of PIK3CA mutations not present in the therascreen companion diagnostic assay or identified by other sequencing-based assays needs further investigation.
    Keywords:  Alpelisib; Breast cancer; Companion diagnostic; Hotspot mutations; Mutations; PIK3CA; Therascreen; ctDNA
    DOI:  https://doi.org/10.1186/s13058-020-01284-9
  4. J Biol Chem. 2020 May 14. pii: jbc.RA120.013223. [Epub ahead of print]
    Collins MP, Stransky LA, Forgac M.
      The vacuolar H+-ATPase (V-ATPase) is an ATP-dependent proton pump that is essential for cellular homeostasis. V-ATPase activity is controlled by regulated assembly of the enzyme from its component V1 and V0 domains. We previously reported that amino acid starvation rapidly increases V-ATPase assembly and activity in mammalian lysosomes, but the signaling pathways controlling this effect are unknown. In testing inhibitors of pathways important for controlling cellular metabolism, we found here that the cAMP-dependent protein kinase (PKA) inhibitor H89 increases lysosomal V-ATPase activity and blocks any further change upon starvation. The AMP-activated protein kinase (AMPK) inhibitor dorsomorphin decreased lysosomal V-ATPase activity and also blocked any increase upon starvation. However, CRISPR-mediated gene editing revealed that PKA and AMPK are not required for the starvation-dependent increase in lysosomal V-ATPase activity, indicating that H89 and dorsomorphin modify V-ATPase activity through other cellular targets. We next found that the AKT Ser/Thr kinase (AKT) inhibitor MK2206 blocks the starvation-dependent increase in lysosomal V-ATPase activity without altering basal activity. Expression of AKT1 or AKT3, but not AKT2, was required for increased lysosomal V-ATPase activity in response to amino acid starvation in mouse fibroblasts. Finally, HEK293T cells expressing only AKT1 responded normally to starvation, whereas cells expressing only AKT2 displayed a significantly reduced increase in V-ATPase activity and assembly upon starvation. These results show that AKT is required for controlling the rapid response of lysosomal V-ATPase activity to changes in amino acid availability and that this response depends on specific AKT isoforms.
    Keywords:  Akt PKB; CRISPR/Cas; MK2206; amino acid homeostasis; kinase signaling; lysosomal acidification; nutient sensing; pH regulation; proton transport; vacuolar ATPase
    DOI:  https://doi.org/10.1074/jbc.RA120.013223
  5. Oncotarget. 2020 Apr 28. 11(17): 1478-1492
    Litchfield LM, Boehnke K, Brahmachary M, Mur C, Bi C, Stephens JR, Sauder JM, Gutiérrez SM, McNulty AM, Ye XS, Wu W, Lallena MJ, Gong X, Merzoug FF, Jansen VM, Buchanan SG.
      Aberrant activation of mitogenic signaling pathways in cancer promotes growth and proliferation of cells by activating mTOR and S6 phosphorylation, and D-cyclin kinases and Rb phosphorylation, respectively. Correspondingly, inhibition of phosphorylation of both Rb and S6 is required for robust anti-tumor efficacy of drugs that inhibit cell signaling. The best-established mechanism of mTOR activation in cancer is via PI3K/Akt signaling, but mTOR activity can also be stimulated by CDK4 and PIM kinases. In this study, we show that the CDK4/6 inhibitor abemaciclib inhibits PIM kinase and S6 phosphorylation in cancer cells and concurrent inhibition of PIM, CDK4, and CDK6 suppresses both S6 and Rb phosphorylation. TSC2 or PIK3CA mutations obviate the requirement for PIM kinase and circumvent the inhibition of S6 phosphorylation by abemaciclib. Combination with a PI3K inhibitor restored suppression of S6 phosphorylation and synergized to curtail cell growth. By combining abemaciclib with a PI3K inhibitor, three pathways (Akt, PIM, and CDK4) to mTOR activation are neutralized, suggesting a potential combination strategy for the treatment of PIK3CA-mutant ER+ breast cancer.
    Keywords:  CDK4/6; PIM; S6; abemaciclib; mTOR
    DOI:  https://doi.org/10.18632/oncotarget.27539
  6. Front Mol Biosci. 2020 ;7 72
    Kong D, Hughes CJ, Ford HL.
      With the exception of non-melanoma skin cancer, breast cancer is the most frequently diagnosed malignant disease among women, with the majority of mortality being attributable to metastatic disease. Thus, even with improved early screening and more targeted treatments which may enable better detection and control of early disease progression, metastatic disease remains a significant problem. While targeted therapies exist for breast cancer patients with particular subtypes of the disease (Her2+ and ER/PR+), even in these subtypes the therapies are often not efficacious once the patient's tumor metastasizes. Increases in stemness or epithelial-to-mesenchymal transition (EMT) in primary breast cancer cells lead to enhanced plasticity, enabling tumor progression, therapeutic resistance, and distant metastatic spread. Numerous signaling pathways, including MAPK, PI3K, STAT3, Wnt, Hedgehog, and Notch, amongst others, play a critical role in maintaining cell plasticity in breast cancer. Understanding the cellular and molecular mechanisms that regulate breast cancer cell plasticity is essential for understanding the biology of breast cancer progression and for developing novel and more effective therapeutic strategies for targeting metastatic disease. In this review we summarize relevant literature on mechanisms associated with breast cancer plasticity, tumor progression, and drug resistance.
    Keywords:  EMT; breast cancer; cancer stem cell; metastasis; plasticity
    DOI:  https://doi.org/10.3389/fmolb.2020.00072
  7. Nat Commun. 2020 May 12. 11(1): 2375
    Ku AA, Hu HM, Zhao X, Shah KN, Kongara S, Wu D, McCormick F, Balmain A, Bandyopadhyay S.
      Synthetic lethal screens have the potential to identify new vulnerabilities incurred by specific cancer mutations but have been hindered by lack of agreement between studies. In the case of KRAS, we identify that published synthetic lethal screen hits significantly overlap at the pathway rather than gene level. Analysis of pathways encoded as protein networks could identify synthetic lethal candidates that are more reproducible than those previously reported. Lack of overlap likely stems from biological rather than technical limitations as most synthetic lethal phenotypes are strongly modulated by changes in cellular conditions or genetic context, the latter determined using a pairwise genetic interaction map that identifies numerous interactions that suppress synthetic lethal effects. Accounting for pathway, cellular and genetic context nominates a DNA repair dependency in KRAS-mutant cells, mediated by a network containing BRCA1. We provide evidence for why most reported synthetic lethals are not reproducible which is addressable using a multi-faceted testing framework.
    DOI:  https://doi.org/10.1038/s41467-020-16078-y
  8. Dev Cell. 2020 Apr 30. pii: S1534-5807(20)30306-3. [Epub ahead of print]
    Sanaki Y, Nagata R, Kizawa D, Léopold P, Igaki T.
      Metabolic diseases such as type 2 diabetes are associated with increased cancer incidence. Here, we show that hyperinsulinemia promotes epithelial tumorigenesis by abrogating cell competition. In Drosophila eye imaginal epithelium, oncogenic scribble (scrib) mutant cells are eliminated by cell competition when surrounded by wild-type cells. Through a genetic screen, we find that flies heterozygous for the insulin receptor substrate chico allow scrib cells to evade cell competition and develop into tumors. Intriguingly, chico is required in the brain's insulin-producing cells (IPCs) to execute cell competition remotely. Mechanistically, chico downregulation in IPCs causes hyperinsulinemia by upregulating a Drosophila insulin Dilp2, which activates insulin-mTOR signaling and thus boosts protein synthesis in scrib cells. A diet-induced increase in insulin levels also triggers scrib tumorigenesis, and pharmacological repression of protein synthesis prevents hyperinsulinemia-induced scrib overgrowth. Our findings provide an in vivo mechanistic link between metabolic disease and cancer risk via systemic regulation of cell competition.
    Keywords:  Drosophila; cancer; cell competition; hyperinsulinemia; insulin; tumor suppression
    DOI:  https://doi.org/10.1016/j.devcel.2020.04.008
  9. Autophagy. 2020 May 13.
    Muñoz-Guardiola P, Casas J, Megías-Roda E, Solé S, Perez-Montoyo H, Yeste-Velasco M, Erazo T, Diéguez-Martínez N, Espinosa-Gil S, Muñoz-Pinedo C, Yoldi G, Abad JL, Segura MF, Moran T, Romeo M, Bosch-Barrera J, Oaknin A, Alfón J, Domènech C, Fabriàs G, Velasco G, Lizcano JM.
      ABTL0812 is a first-in-class small molecule with anti-cancer activity, which is currently in clinical evaluation in a phase 2 trial in patients with advanced endometrial and squamous non-small cell lung carcinoma (NCT03366480). Previously, we showed that ABTL0812 induces TRIB3 pseudokinase expression, resulting in the inhibition of the AKT-MTORC1 axis and macroautophagy/autophagy-mediated cancer cell death. However, the precise molecular determinants involved in the cytotoxic autophagy caused by ABTL0812 remained unclear. Using a wide range of biochemical and lipidomic analyses, we demonstrated that ABTL0812 increases cellular long-chain dihydroceramides by impairing DEGS1 (delta 4-desaturase, sphingolipid 1) activity, which resulted in sustained ER stress and activated unfolded protein response (UPR) via ATF4-DDIT3-TRIB3 that ultimately promotes cytotoxic autophagy in cancer cells. Accordingly, pharmacological manipulation to increase cellular dihydroceramides or incubation with exogenous dihydroceramides resulted in ER stress, UPR and autophagy-mediated cancer cell death. Importantly, we have optimized a method to quantify mRNAs in blood samples from patients enrolled in the ongoing clinical trial, who showed significant increased DDIT3 and TRIB3 mRNAs. This is the first time that UPR markers are reported to change in human blood in response to any drug treatment, supporting their use as pharmacodynamic biomarkers for compounds that activate ER stress in humans. Finally, we found that MTORC1 inhibition and dihydroceramide accumulation synergized to induce autophagy and cytotoxicity, phenocopying the effect of ABTL0812. Given the fact that ABTL0812 is under clinical development, our findings support the hypothesis that manipulation of dihydroceramide levels might represents a new therapeutic strategy to target cancer.
    Keywords:  ER stress; UPR; autophagy; cancer; clinical trial; dihydroceramide
    DOI:  https://doi.org/10.1080/15548627.2020.1761651
  10. Cancer Res. 2020 May 11. pii: canres.2884.2019. [Epub ahead of print]
    Feng Y, Mischler WJ, Gurung AC, Kavanagh TR, Androsov G, Sadow PM, Herbert ZT, Priolo C.
      Tuberous Sclerosis Complex (TSC) is an autosomal dominant disease characterized by multi-organ hamartomas, including renal angiomyolipomas and pulmonary lymphangioleiomyomatosis (LAM). TSC2 deficiency leads to hyperactivation of mammalian Target of Rapamycin Complex 1 (mTORC1), a master regulator of cell growth and metabolism. Phospholipid metabolism is dysregulated upon TSC2 loss, causing enhanced production of lysophosphatidylcholine (LPC) species by TSC2-deficient tumor cells. LPC is the major substrate of the secreted lysophospholipase D autotaxin (ATX), which generates two bioactive lipids, lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P). We report here that ATX expression is upregulated in human renal angiomyolipoma-derived TSC2-deficient cells compared to TSC2 add-back cells. Inhibition of ATX via the clinically developed compound GLPG1690 suppressed TSC2-loss associated oncogenicity in vitro and in vivo and induced apoptosis in TSC2-deficient cells. GLPG1690 suppressed Akt and Erk1/2 signaling and profoundly impacted the transcriptome of these cells while inducing minor gene expression changes in TSC2 add-back cells. RNAseq studies revealed transcriptomic signatures of LPA and S1P, suggesting an LPA/S1P-mediated reprogramming of the TSC lipidome. In addition, supplementation of LPA or S1P rescued proliferation and viability, neutral lipid content, and Akt or Erk1/2 signaling in human TSC2-deficient cells treated with GLPG1690. Importantly, TSC-associated renal angiomyolipomas have higher expression of LPA receptor 1 and S1P receptor 3 compared to normal kidney. These studies increase our understanding of TSC2-deficient cell metabolism, leading to novel potential therapeutic opportunities for TSC and LAM.
    DOI:  https://doi.org/10.1158/0008-5472.CAN-19-2884
  11. Hum Mol Genet. 2020 May 11. pii: ddaa086. [Epub ahead of print]
    Madhivanan K, Ramadesikan S, Hsieh WC, Aguilar MC, Hanna CB, Bacallao RL, Aguilar RC.
      Lowe Syndrome (LS) is an X-linked developmental disease characterized by cognitive deficiencies, bilateral congenital cataracts and renal dysfunction. Unfortunately, this disease leads to the early death of affected children often due to kidney failure. Although this condition was first described in the early fifties and the affected gene (OCRL1) was identified in the early nineties, its pathophysiological-mechanism is not fully understood and there is no LS-specific cure available to patients. Here we report two important signaling pathways affected in LS patient cells. While RhoGTPase signaling abnormalities led to adhesion and spreading defects as compared to normal controls, PI3K/mTOR hyperactivation interfered with primary cilia assembly (scenario also observed in other ciliopathies with compromised kidney function). Importantly, we identified two FDA-approved drugs able to ameliorate these phenotypes. Specifically, statins mitigated adhesion and spreading abnormalities while rapamycin facilitated ciliogenesis in LS patient cells. However, no single drug was able to alleviate both phenotypes. Based on these and other observations, we speculate that Ocrl1 has dual, independent functions supporting proper RhoGTPase and PI3K/mTOR signaling. Therefore, this study suggest that Ocrl1-deficiency leads to signaling defects likely to require combinatorial drug treatment to suppress patient phenotypes and symptoms.
    DOI:  https://doi.org/10.1093/hmg/ddaa086
  12. Mod Pathol. 2020 May 13.
    Skala SL, Liu CJ, Udager AM, Sciallis AP.
      Ovarian germ cell tumors, including yolk sac tumors, are most commonly diagnosed in children and young women. Most so-called yolk sac tumors reported in women >35 years old have been associated with an epithelial proliferation (endometriosis or carcinoma). Here, we describe eight cases clinically diagnosed as uterine or ovarian germ cell tumors in women >35 years old. In addition to routine morphologic examination and immunohistochemical evaluation, we present data from targeted next-generation sequencing (NGS) and isochromosome (12p) fluorescence in situ hybridization (FISH). We identified two groups of tumors with mixed germ cell and epithelial features: (1) tumors with background endometriosis and endometrioid carcinoma-like mutations (PTEN, PIK3CA, FGFR2, and CTNNB1), and (2) high-grade morphology, presumptive presence of isochromosome (12p) by FISH, and TP53 or PIK3CA mutations. These findings support the notion that the "germ cell tumor" component of these tumors is often somatically derived. Two tumors in our cohort were from premenopausal women; one showed no detectable mutations by NGS (suggestive of germ cell derivation), whereas the other showed PIK3CA, PTEN, and CTNNB1 mutations (suggestive of somatic derivation). Accurate classification of these tumors is likely important for selection of appropriate chemotherapy.
    DOI:  https://doi.org/10.1038/s41379-020-0548-6
  13. Breast Cancer Res. 2020 May 11. 22(1): 44
    Burkholder A, Akrobetu D, Pandiri AR, Ton K, Kim S, Labow BI, Nuzzi LC, Firriolo JM, Schneider SS, Fenton SE, Shaw ND.
      BACKGROUND: Early life environmental exposures affect breast development and breast cancer risk in adulthood. The breast is particularly vulnerable during puberty when mammary epithelial cells proliferate exponentially. In overweight/obese (OB) women, inflammation increases breast aromatase expression and estrogen synthesis and promotes estrogen-receptor (ER)-positive breast cancer. In contrast, recent epidemiological studies suggest that obesity during childhood decreases future breast cancer risk. Studies on environmental exposures and breast cancer risk have thus far been limited to animal models. Here, we present the first interrogation of the human adolescent breast at the molecular level and investigate how obesity affects the immature breast.METHODS: We performed RNA-seq in 62 breast tissue samples from adolescent girls/young women (ADOL; mean age 17.8 years) who underwent reduction mammoplasty. Thirty-one subjects were non-overweight/obese (NOB; mean BMI 23.4 kg/m2) and 31 were overweight/obese (OB; BMI 32.1 kg/m2). We also compared our data to published mammary transcriptome datasets from women (mean age 39 years) and young adult mice, rats, and macaques.
    RESULTS: The ADOL breast transcriptome showed limited (30%) overlap with other species, but 88% overlap with adult women for the 500 most highly expressed genes in each dataset; only 43 genes were shared by all groups. In ADOL, there were 120 differentially expressed genes (DEG) in OB compared with NOB samples (padj < 0.05). Based on these DEG, Ingenuity Pathway Analysis (IPA) identified the cytokines CSF1 and IL-10 and the chemokine receptor CCR2 as among the most highly activated upstream regulators, suggesting increased inflammation in the OB breast. Classical ER targets (e.g., PR, AREG) were not differentially expressed, yet IPA identified the ER and PR and growth factors/receptors (VEGF, HGF, HER3) and kinases (AKT1) involved in hormone-independent ER activation as activated upstream regulators in OB breast tissue.
    CONCLUSIONS: These studies represent the first investigation of the human breast transcriptome during late puberty/young adulthood and demonstrate that obesity is associated with a transcriptional signature of inflammation which may augment estrogen action in the immature breast microenvironment. We anticipate that these studies will prompt more comprehensive cellular and molecular investigations of obesity and its effect on the breast during this critical developmental window.
    Keywords:  Adolescent; Obesity; RNA-seq
    DOI:  https://doi.org/10.1186/s13058-020-01279-6
  14. Biochim Biophys Acta Mol Cell Biol Lipids. 2020 May 10. pii: S1388-1981(20)30129-3. [Epub ahead of print] 158737
    Xie H, Heier C, Kien B, Vesely PW, Tang Z, Sexl V, Schoiswohl G, Strießnig-Bina I, Hoefler G, Zechner R, Schweiger M.
      Aberrant fatty acid (FA) metabolism is a hallmark of proliferating cells, including untransformed fibroblasts or cancer cells. Lipolysis of intracellular triglyceride (TG) stores by adipose triglyceride lipase (ATGL) provides an important source of FAs serving as energy substrates, signaling molecules, and precursors for membrane lipids. To investigate if ATGL-mediated lipolysis impacts cell proliferation, we modified ATGL activity in murine embryonic fibroblasts (MEFs) and in five different cancer cell lines to determine the consequences on cell growth and metabolism. Genetic or pharmacological inhibition of ATGL in MEFs causes impaired FA oxidation, decreased ROS production, and a substrate switch from FA to glucose leading to decreased AMPK-mTOR signaling and higher cell proliferation rates. ATGL expression in these cancer cells is low when compared to MEFs. Additional ATGL knockdown in cancer cells did not significantly affect cellular lipid metabolism or cell proliferation whereas the ectopic overexpression of ATGL increased lipolysis and reduced proliferation. In contrast to ATGL silencing, pharmacological inhibition of ATGL by Atglistatin© impeded the proliferation of diverse cancer cell lines, which points at an ATGL-independent effect. Our data indicate a crucial role of ATGL-mediated lipolysis in the regulation of cell proliferation. The observed low ATGL activity in cancer cells may represent an evolutionary selection process and mechanism to sustain high cell proliferation rates. As the increasing ATGL activity decelerates proliferation of five different cancer cell lines this may represent a novel therapeutic strategy to counteract uncontrolled cell growth.
    Keywords:  ATGL; Cancer; Lipid; Lipolysis; Proliferation
    DOI:  https://doi.org/10.1016/j.bbalip.2020.158737
  15. Cell Stem Cell. 2020 May 07. pii: S1934-5909(20)30137-5. [Epub ahead of print]26(5): 632-656
    McKinley KL, Castillo-Azofeifa D, Klein OD.
      Defining the mechanisms that generate specialized cell types and coordinate their functions is critical for understanding organ development and renewal. New tools and discoveries are challenging and refining our definitions of a cell type. A rapidly growing toolkit for single-cell analyses has expanded the number of markers that can be assigned to a cell simultaneously, revealing heterogeneity within cell types that were previously regarded as homogeneous populations. Additionally, cell types defined by specific molecular markers can exhibit distinct, context-dependent functions; for example, between tissues in homeostasis and those responding to damage. Here we review the current technologies used to identify and characterize cells, and we discuss how experimental and pathological perturbations are adding increasing complexity to our definitions of cell identity.
    Keywords:  cell competition; cell type; microscopy; organoid; plasticity; scRNA-seq; smFISH; stem cell
    DOI:  https://doi.org/10.1016/j.stem.2020.03.015
  16. Trends Biochem Sci. 2020 May 10. pii: S0968-0004(20)30108-0. [Epub ahead of print]
    Wilson BD, Soh HT.
      Analytical technologies based on binding assays have evolved substantially since their inception nearly 60 years ago, but our conceptual understanding of molecular recognition has not kept pace. Contemporary technologies, such as single-molecule and digital measurements, have challenged, or even rendered obsolete, core concepts behind conventional binding assay design. Here, we explore the fundamental principles underlying molecular recognition systems, which we consider in terms of signals generated through concentration-dependent shifts in equilibrium. We challenge certain orthodoxies related to binding-based detection assays, including the primary importance of a low dissociation constant (KD) and the extent to which this parameter constrains dynamic range and limit of detection. Lastly, we identify key principles for designing binding assays that are optimally suited for a given detection application.
    Keywords:  Langmuir isotherm; affinity reagent; binding assays; digital detection; specificity
    DOI:  https://doi.org/10.1016/j.tibs.2020.04.005