bims-pideca Biomed News
on Class IA PI3K signalling in development and cancer
Issue of 2021‒02‒21
nineteen papers selected by
Ralitsa Radostinova Madsen
University College London Cancer Institute

  1. Mol Cell. 2021 Feb 18. pii: S1097-2765(21)00053-8. [Epub ahead of print]81(4): 708-723.e5
    Mukherjee R, Vanaja KG, Boyer JA, Gadal S, Solomon H, Chandarlapaty S, Levchenko A, Rosen N.
      The PI3K pathway regulates cell metabolism, proliferation, and migration, and its dysregulation is common in cancer. We now show that both physiologic and oncogenic activation of PI3K signaling increase the expression of its negative regulator PTEN. This limits the duration of the signal and output of the pathway. Physiologic and pharmacologic inhibition of the pathway reduces PTEN and contributes to the rebound in pathway activity in tumors treated with PI3K inhibitors and limits their efficacy. Regulation of PTEN is due to mTOR/4E-BP1-dependent control of its translation and is lost when 4E-BP1 is deleted. Translational regulation of PTEN is therefore a major homeostatic regulator of physiologic PI3K signaling and plays a role in reducing the pathway activation by oncogenic PIK3CA mutants and the antitumor activity of PI3K pathway inhibitors. However, pathway output is hyperactivated in tumor cells with coexistent PI3K mutation and loss of PTEN function.
    Keywords:  4E-BP; BYL-719; PI3K signaling; PTEN regulation; PTEN translation; computational model of PI3K signaling; growth factor signaling; mTOR; negative feedback; resistance to PI3K inhibition
  2. Physiol Rev. 2021 Feb 18.
    Szwed A, Kim E, Jacinto E.
      Cells metabolize nutrients for biosynthetic and bioenergetic needs to fuel growth and proliferation. The uptake of nutrients from the environment and their intracellular metabolism is a highly controlled process that involves crosstalk between growth signaling and metabolic pathways. Despite constant fluctuations in nutrient availability and environmental signals, normal cells restore metabolic homeostasis to maintain cellular functions and prevent disease. A central signaling molecule that integrates growth with metabolism is the mechanistic target of rapamycin (mTOR). mTOR is a protein kinase that responds to levels of nutrients and growth signals. mTOR forms two protein complexes, mTORC1, which is sensitive to rapamycin and mTORC2, which is not directly inhibited by this drug. Rapamycin has facilitated the discovery of the various functions of mTORC1 in metabolism. Genetic models that disrupt either mTORC1 or mTORC2 have expanded our knowledge on their cellular, tissue as well as systemic functions in metabolism. Nevertheless, our knowledge on the regulation and functions of mTORC2, particularly in metabolism, has lagged behind. Since mTOR is an important target for cancer, aging and other metabolism-related pathologies, understanding the distinct and overlapping regulation and functions of the two mTOR complexes is vital for the development of more effective therapeutic strategies. This review will discuss the key discoveries and recent findings on the regulation and metabolic functions of the mTOR complexes. We highlight findings from cancer models, but also discuss other examples of the mTOR-mediated metabolic reprogramming occurring in stem and immune cells, type 2 diabetes/obesity, neurodegenerative disorders and aging.
    Keywords:  cancer metabolism; mTOR; mTORC; metabolic reprogramming; metabolism
  3. Cell Rep. 2021 Feb 16. pii: S2211-1247(21)00063-2. [Epub ahead of print]34(7): 108750
    Kondo H, Ratcliffe CDH, Hooper S, Ellis J, MacRae JI, Hennequart M, Dunsby CW, Anderson KI, Sahai E.
      Inter-cellular heterogeneity in metabolic state has been proposed to influence many cancer phenotypes, including responses to targeted therapy. Here, we track the transitions and heritability of metabolic states in single PIK3CA mutant breast cancer cells, identify non-genetic glycolytic heterogeneity, and build on observations derived from methods reliant on bulk analyses. Using fluorescent biosensors in vitro and in tumors, we have identified distinct subpopulations of cells whose glycolytic and mitochondrial metabolism are regulated by combinations of phosphatidylinositol 3-kinase (PI3K) signaling, bromodomain activity, and cell crowding effects. The actin severing protein cofilin, as well as PI3K, regulates rapid changes in glucose metabolism, whereas treatment with the bromodomain inhibitor slowly abrogates a subpopulation of cells whose glycolytic activity is PI3K independent. We show how bromodomain function and PI3K signaling, along with actin remodeling, independently modulate glycolysis and how targeting these pathways affects distinct subpopulations of cancer cells.
    Keywords:  FRET imaging; PI3K signaling; breast cancer; cofilin; intra-tumor heterogeneity; intravital imaging; tumor metabolism
  4. Clin Cancer Res. 2021 Feb 18. pii: clincanres.4879.2020. [Epub ahead of print]
    Sharma P, Abramson VG, O'Dea AP, Nye L, Mayer IA, Pathak HB, Hoffmann M, Stecklein SR, Elia M, Lewis S, Scott J, De Jong JA, Wang YY, Yoder R, Schwensen K, Finke K, Heldstab J, LaFaver S, Williamson S, Phadnis MA, Reed GA, Kimler BF, Khan QJ, Godwin AK.
      PURPOSE: PIK3CA mutations are common in breast cancer and promote tumor progression and treatment resistance. We conducted a phase I/II trial of alpelisib (α-specific PI3K inhibitor) plus nab-paclitaxel in patients with HER2-negative metastatic breast cancer (MBC).EXPERIMENTAL DESIGN: Eligible patients had HER2-negative MBC with any number of prior chemotherapies. Phase I was 3+3 dose-escalation design with three dose levels of alpelisib (250mg-300mg-350mg) daily, plus nab-paclitaxel 100mg/m2 D1-8-15 every 28 days. Phase II was according to Simon's two-stage design. PIK3CA mutations in tumor/circulating-tumor DNA (ctDNA) were assessed. Primary endpoints were recommended phase 2 dose (RP2D) and objective response rate (ORR). Additional endpoints included safety, pharmacokinetics, PFS, association of PIK3CA mutation with outcomes.
    RESULTS: 43 patients enrolled (phase I=13, phase II=30). 84% had visceral disease, 84% had prior taxane. No dose-limiting toxicities occurred in phase I. RP2D was alpelisib 350mg daily +nab-paclitaxel 100mg/m2 D1-8-15. Hyperglycemia (G3:26%,G4:0%), neutropenia (G3:23%,G4:7%), diarrhea (G3:5%,G4:0%), and rash (G3:7%,G4:0%) were most common adverse events. Among 42 evaluable patients, ORR was 59% (CR=7%, PR=52%), 21% of whom had response lasting >12 months; median PFS was 8.7 months. 40% demonstrated tumor and/or ctDNA PIK3CA mutation; patients with tumor/ctDNA mutation demonstrated better PFS compared to those without mutation (11.9 vs 7.5 months, HR=0.44, p=0.027). Patients with normal metabolic status had longer PFS compared to prediabetic/diabetic patients (12.0 vs 7.5 months, p=0.014). No pharmacokinetic interactions were detected.
    CONCLUSIONS: Alpelisib plus nab-paclitaxel combination was well-tolerated and shows encouraging efficacy, especially in patients with PIK3CA-mutated tumor/ctDNA. Impact of metabolic status on response to this combination merits further investigation.
  5. Nat Commun. 2021 02 17. 12(1): 1088
    Jin S, Guerrero-Juarez CF, Zhang L, Chang I, Ramos R, Kuan CH, Myung P, Plikus MV, Nie Q.
      Understanding global communications among cells requires accurate representation of cell-cell signaling links and effective systems-level analyses of those links. We construct a database of interactions among ligands, receptors and their cofactors that accurately represent known heteromeric molecular complexes. We then develop CellChat, a tool that is able to quantitatively infer and analyze intercellular communication networks from single-cell RNA-sequencing (scRNA-seq) data. CellChat predicts major signaling inputs and outputs for cells and how those cells and signals coordinate for functions using network analysis and pattern recognition approaches. Through manifold learning and quantitative contrasts, CellChat classifies signaling pathways and delineates conserved and context-specific pathways across different datasets. Applying CellChat to mouse and human skin datasets shows its ability to extract complex signaling patterns. Our versatile and easy-to-use toolkit CellChat and a web-based Explorer ( ) will help discover novel intercellular communications and build cell-cell communication atlases in diverse tissues.
  6. EMBO J. 2021 Feb 15. 40(4): e105094
    Li X, Pal DS, Biswas D, Iglesias PA, Devreotes PN.
      The ability of cells to polarize and move toward external stimuli plays a crucial role in development, as well as in normal and pathological physiology. Migrating cells maintain dynamic complementary distributions of Ras activity and of the phospholipid phosphatidylinositol-3,4-bisphosphate (PI(3,4)P2). Here, we show that lagging-edge component PI(3,4)P2 also localizes to retracting leading-edge protrusions and nascent macropinosomes, even in the absence of phosphatidylinositol 3,4,5-trisphosphate (PIP3). Once internalized, macropinosomes break up into smaller PI(3,4)P2-enriched vesicles, which fuse with the plasma membrane at the rear of the cell. Subsequently, the phosphoinositide diffuses toward the front of the cell, where it is degraded. Computational modeling confirms that this cycle gives rise to stable back-to-front gradient. These results uncover a surprising "reverse-fountain flow" of PI(3,4)P2 that regulates polarity.
    Keywords:  cell migration; excitability; membrane flow; neutrophils; refractory period
  7. Mol Syst Biol. 2021 Feb;17(2): e9821
    Hansen AS, Zechner C.
      Cells respond to external signals and stresses by activating transcription factors (TF), which induce gene expression changes. Prior work suggests that signal-specific gene expression changes are partly achieved because different gene promoters exhibit distinct induction dynamics in response to the same TF input signal. Here, using high-throughput quantitative single-cell measurements and a novel statistical method, we systematically analyzed transcriptional responses to a large number of dynamic TF inputs. In particular, we quantified the scaling behavior among different transcriptional features extracted from the measured trajectories such as the gene activation delay or duration of promoter activity. Surprisingly, we found that even the same gene promoter can exhibit qualitatively distinct induction and scaling behaviors when exposed to different dynamic TF contexts. While it was previously known that promoters fall into distinct classes, here we show that the same promoter can switch between different classes depending on context. Thus, promoters can adopt context-dependent "manifestations". Our analysis suggests that the full complexity of signal processing by genetic circuits may be significantly underestimated when studied in only specific contexts.
    Keywords:  Bayesian inference; Msn2; manifestation; promoter class switching; transcription factor dynamics
  8. Elife. 2021 Feb 15. pii: e61951. [Epub ahead of print]10
    Jacob RS, Eichmann C, Dema A, Mercadante D, Selenko P.
      The Parkinson's disease protein α-synuclein (aSyn) promotes membrane fusion and fission by interacting with various negatively charged phospholipids. Despite postulated roles in endocytosis and exocytosis, plasma membrane (PM) interactions of αSyn are poorly understood. Here, we show that phosphatidylinositol 4,5-bisphosphate (PIP2) and phosphatidylinositol 3,4,5-trisphosphate (PIP3), two highly acidic components of inner PM leaflets, mediate plasma membrane localization of endogenous pools of αSyn in A2780, HeLa, SK-MEL-2 and differentiated and undifferentiated neuronal SH-SY5Y cells. We demonstrate that αSyn binds to reconstituted PIP2-membranes in a helical conformation in vitro and that PIP2 synthesizing kinases and hydrolyzing phosphatases reversibly redistribute αSyn in cells. We further delineate that αSyn-PM targeting follows phosphoinositide-3 kinase (PI3K)-dependent changes of cellular PIP2 and PIP3 levels, which collectively suggests that phosphatidylinositol polyphosphates contribute to αSyn's cellular function(s) at the plasma membrane.
    Keywords:  neuroscience
  9. Cell Rep. 2021 Feb 16. pii: S2211-1247(21)00057-7. [Epub ahead of print]34(7): 108744
    Wu D, Yan Y, Wei T, Ye Z, Xiao Y, Pan Y, Orme JJ, Wang D, Wang L, Ren S, Huang H.
      Acquisition of resistance to phosphatidylinositol 3-kinase (PI3K)/AKT-targeted monotherapy implies the existence of common resistance mechanisms independent of cancer type. Here, we demonstrate that PI3K/AKT inhibitors cause glycolytic crisis, acetyl-coenzyme A (CoA) shortage, and a global decrease in histone acetylation. In addition, PI3K/AKT inhibitors induce drug resistance by selectively augmenting histone H3 lysine 27 acetylation (H3K27ac) and binding of CBP/p300 and BRD4 proteins at a subset of growth factor and receptor (GF/R) gene loci. BRD4 occupation at these loci and drug-resistant cell growth are vulnerable to both bromodomain and histone deacetylase (HDAC) inhibitors. Little or no occupation of HDAC proteins at the GF/R gene loci underscores the paradox that cells respond equivalently to the two classes of inhibitors with opposite modes of action. Targeting this unique acetyl-histone-related vulnerability offers two clinically viable strategies to overcome PI3K/AKT inhibitor resistance in different cancers.
  10. Mol Cell Endocrinol. 2021 Feb 16. pii: S0303-7207(21)00057-5. [Epub ahead of print] 111213
    Lero MW, Shaw LM.
      This review highlights the significance of the insulin receptor (IR) and insulin-like growth factor-1 receptor (IGF-1R) signaling pathway in cancer and assesses its potential as a therapeutic target. Our emphasis is on breast cancer, but this pathway is central to the behavior of many cancers. An understanding of how IR/IGF-1R signaling contributes to the function of the normal mammary gland provides a foundation for understanding its aberrations in breast cancer. Specifically, dysregulation of the expression and function of ligands (insulin, IGF-1 and IGF-2), receptors and their downstream signaling effectors drive breast cancer initiation and progression, often in a subtype-dependent manner. Efforts to target this pathway for the treatment of cancer have been hindered by several factors including a lack of biomarkers to select patients that could respond to targeted therapy and adverse effects on normal metabolism. To this end, we discuss ongoing efforts aimed at overcoming such obstacles.
    Keywords:  Breast Cancer; IGF-1R; Insulin; Insulin-like Growth Factor (IGF); Signal Transduction; Therapy; insulin receptor
  11. J Clin Invest. 2021 Feb 15. pii: 142245. [Epub ahead of print]131(4):
    Angelidi AM, Filippaios A, Mantzoros CS.
      Severe insulin resistance syndromes are a heterogeneous group of rare disorders characterized by profound insulin resistance, substantial metabolic abnormalities, and a variety of clinical manifestations and complications. The etiology of these syndromes may be hereditary or acquired, due to defects in insulin potency and action, cellular responsiveness to insulin, and/or aberrations in adipose tissue function or development. Over the past decades, advances in medical technology, particularly in genomic technologies and genetic analyses, have provided insights into the underlying pathophysiological pathways and facilitated the more precise identification of several of these conditions. However, the exact cellular and molecular mechanisms of insulin resistance have not yet been fully elucidated for all syndromes. Moreover, in clinical practice, many of the syndromes are often misdiagnosed or underdiagnosed. The majority of these disorders associate with an increased risk of severe complications and mortality; thus, early identification and personalized clinical management are of the essence. This Review aims to categorize severe insulin resistance syndromes by disease process, including insulin receptor defects, signaling defects, and lipodystrophies. We also highlight several complex syndromes and emphasize the need to identify patients, investigate underlying disease mechanisms, and develop specific treatment regimens.
  12. Biomolecules. 2021 Jan 25. pii: 150. [Epub ahead of print]11(2):
    Hedges CP, Boix J, Jaiswal JK, Shetty B, Shepherd PR, Merry TL.
      BYL719 (alpelisib) is a small molecule inhibitor of PI3K p110α developed for cancer therapy. Targeted suppression of PI3K has led to lifespan extension in rodents and model organisms. If PI3K inhibitors are to be considered as an aging therapeutic, it is important to understand the potential consequences of long-term exposure, and the most practical way to achieve this is through diet administration. Here, we investigated the pharmacokinetics of BYL719 delivered in diet and the efficacy of BYL719 to suppress insulin signaling when administered in the diet of 8-month-old male and female mice. Compared to oral gavage, diet incorporation resulted in a lower peak plasma BYL719 (3.6 vs. 9.2 μM) concentration but similar half-life (~1.5 h). Consuming BYL719 resulted in decreased insulin signaling in liver and muscle within 72 h, and mice still showed impaired glucose tolerance and insulin sensitivity following 6 weeks of access to a diet containing 0.3 g/kg BYL719. However, consuming BYL719 did not affect food intake, body mass, muscle function (rotarod and hang time performance) or cognitive behaviors. This provides evidence that BYL719 has long-term efficacy without major toxicity or side effects, and suggests that administering BYL719 in diet is suitable for studying the effect of pharmacological suppression of PI3K p110α on aging and metabolic function.
    Keywords:  BYL-719; aging; glucose tolerance; insulin signaling; pharmacokinetics
  13. Nat Commun. 2021 02 17. 12(1): 1089
    Noël F, Massenet-Regad L, Carmi-Levy I, Cappuccio A, Grandclaudon M, Trichot C, Kieffer Y, Mechta-Grigoriou F, Soumelis V.
      Cell-to-cell communication can be inferred from ligand-receptor expression in cell transcriptomic datasets. However, important challenges remain: global integration of cell-to-cell communication; biological interpretation; and application to individual cell population transcriptomic profiles. We develop ICELLNET, a transcriptomic-based framework integrating: 1) an original expert-curated database of ligand-receptor interactions accounting for multiple subunits expression; 2) quantification of communication scores; 3) the possibility to connect a cell population of interest with 31 reference human cell types; and 4) three visualization modes to facilitate biological interpretation. We apply ICELLNET to three datasets generated through RNA-seq, single-cell RNA-seq, and microarray. ICELLNET reveals autocrine IL-10 control of human dendritic cell communication with up to 12 cell types. Four of them (T cells, keratinocytes, neutrophils, pDC) are further tested and experimentally validated. In summary, ICELLNET is a global, versatile, biologically validated, and easy-to-use framework to dissect cell communication from individual or multiple cell-based transcriptomic profiles.
  14. J Clin Endocrinol Metab. 2021 Feb 19. pii: dgab100. [Epub ahead of print]
    Laurenti MC, Dalla Man C, Varghese RT, Andrews JC, Jones JG, Barosa C, Rizza RA, Matveyenko A, De Nicolao G, Bailey KR, Cobelli C, Vella A.
      OBJECTIVE: Pulsatile insulin secretion is impaired in diseases such as type 2 diabetes that are characterized by insulin resistance. This has led to the suggestion that changes in insulin pulsatility directly impair insulin signaling. We sought to examine the effects of pulse characteristics on insulin action in humans, hypothesizing that a decrease in pulse amplitude or frequency is associated with impaired hepatic insulin action.METHODS: We studied 29 nondiabetic subjects on two occasions. On one occasion, hepatic and peripheral insulin action was measured using a euglycemic clamp. The deuterated water method was used to estimate the contribution of gluconeogenesis to endogenous glucose production. On a separate study day we utilized nonparametric stochastic deconvolution of frequently sampled peripheral C-peptide concentrations during fasting to reconstruct portal insulin secretion. In addition to measuring basal and pulsatile insulin secretion, we used Approximate Entropy (ApEn) to measure orderliness and Fourier transform to measure the average, and the dispersion of, insulin pulse frequencies.
    RESULTS: In univariate analysis, basal insulin secretion (R 2 = 0.16) and insulin pulse amplitude (R 2 = 0.09), correlated weakly with insulin-induced suppression of gluconeogenesis. However, after adjustment for age, sex and weight these associations were no longer significant. The other pulse characteristics also did not correlate with the ability of insulin to suppress endogenous glucose production (and gluconeogenesis), or to stimulate glucose disappearance.
    CONCLUSIONS: Overall, our data demonstrate that insulin pulse characteristics, considered independently of other factors, do not correlate with measures of hepatic and peripheral insulin sensitivity in non-diabetic humans.
    Keywords:  C-peptide kinetics; endogenous glucose production; gluconeogenesis; glucose disappearance; insulin action; insulin pulses
  15. Immunometabolism. 2021 ;pii: e210007. [Epub ahead of print]3(1):
    Abdullah L, Hills LB, Winter EB, Huang YH.
      Akt kinases translate various external cues into intracellular signals that control cell survival, proliferation, metabolism and differentiation. This review discusses the requirement for Akt and its targets in determining the fate and function of T cells. We discuss the importance of Akt at various stages of T cell development including β-selection during which Akt fulfills the energy requirements of highly proliferative DN3 cells. Akt also plays an integral role in CD8 T cell biology where its regulation of Foxo transcription factors and mTORC1 metabolic activity controls effector versus memory CD8 T cell differentiation. Finally, Akt promotes the differentiation of naïve CD4 T cells into Th1, Th17 and Tfh cells but inhibits the development of Treg cells. We also highlight how modulating Akt in T cells is a promising avenue for enhancing cell-based cancer immunotherapy.
    Keywords:  Akt; CD8 T cells; Foxo; T cell differentiation; Tfh; Th1; Th17; Treg; mTOR; thymocytes
  16. Cell Rep. 2021 Jan 26. pii: S2211-1247(20)31667-3. [Epub ahead of print]34(4): 108678
    Rathore R, Caldwell KE, Schutt C, Brashears CB, Prudner BC, Ehrhardt WR, Leung CH, Lin H, Daw NC, Beird HC, Giles A, Wang WL, Lazar AJ, Chrisinger JSA, Livingston JA, Van Tine BA.
      Osteosarcoma is the most common pediatric and adult primary malignant bone cancer. Curative regimens target the folate pathway, downstream of serine metabolism, with high-dose methotrexate. Here, the rate-limiting enzyme in the biosynthesis of serine from glucose, 3-phosphoglycerate dehydrogenase (PHGDH), is examined, and an inverse correlation between PHGDH expression and relapse-free and overall survival in osteosarcoma patients is found. PHGDH inhibition in osteosarcoma cell lines attenuated cellular proliferation without causing cell death, prompting a robust metabolic analysis to characterize pro-survival compensation. Using metabolomic and lipidomic profiling, cellular response to PHGDH inhibition is identified as accumulation of unsaturated lipids, branched chain amino acids, and methionine cycle intermediates, leading to activation of pro-survival mammalian target of rapamycin complex 1 (mTORC1) signaling. Increased mTORC1 activation sensitizes cells to mTORC1 pathway inhibition, resulting in significant, synergistic cell death in vitro and in vivo. Identifying a therapeutic combination for PHGDH-high cancers offers preclinical justification for a dual metabolism-based combination therapy for osteosarcoma.
    Keywords:  GATOR; PHGDH; SAMTOR; lipid metabolism; mTORC1; methotrexate; one-carbon metabolism; osteosarcoma; perhexiline; serine biosynthesis
  17. Cell Metab. 2021 Feb 10. pii: S1550-4131(21)00056-5. [Epub ahead of print]
    Maguire OA, Ackerman SE, Szwed SK, Maganti AV, Marchildon F, Huang X, Kramer DJ, Rosas-Villegas A, Gelfer RG, Turner LE, Ceballos V, Hejazi A, Samborska B, Rahbani JF, Dykstra CB, Annis MG, Luo JD, Carroll TS, Jiang CS, Dannenberg AJ, Siegel PM, Tersey SA, Mirmira RG, Kazak L, Cohen P.
      Obesity is a major risk factor for adverse outcomes in breast cancer; however, the underlying molecular mechanisms have not been elucidated. To investigate the role of crosstalk between mammary adipocytes and neoplastic cells in the tumor microenvironment (TME), we performed transcriptomic analysis of cancer cells and adjacent adipose tissue in a murine model of obesity-accelerated breast cancer and identified glycine amidinotransferase (Gatm) in adipocytes and Acsbg1 in cancer cells as required for obesity-driven tumor progression. Gatm is the rate-limiting enzyme in creatine biosynthesis, and deletion in adipocytes attenuated obesity-driven tumor growth. Similarly, genetic inhibition of creatine import into cancer cells reduced tumor growth in obesity. In parallel, breast cancer cells in obese animals upregulated the fatty acyl-CoA synthetase Acsbg1 to promote creatine-dependent tumor progression. These findings reveal key nodes in the crosstalk between adipocytes and cancer cells in the TME necessary for obesity-driven breast cancer progression.
    Keywords:  Acsbg1; Gatm; breast cancer; creatine; hypoxia; obesity
  18. Elife. 2021 Feb 17. pii: e61406. [Epub ahead of print]10
    Sun Z, Yao Y, You M, Liu J, Guo W, Qi Z, Wang Z, Wang F, Yuan W, Yu S.
      The kinase PDK1 is a crucial regulator for immune cell development by connecting PI3K to downstream AKT signaling. However, the roles of PDK1 in CD4+ T cell differentiation, especially in T follicular helper (Tfh) cell, remain obscure. Here we reported PDK1 intrinsically promotes the Tfh cell differentiation and germinal center responses upon acute infection by using conditional knockout mice. PDK1 deficiency in T cells caused severe defects in both early differentiation and late maintenance of Tfh cells. The expression of key Tfh regulators was remarkably downregulated in PDK1-deficient Tfh cells, including Tcf7, Bcl6, Icos, and Cxcr5. Mechanistically, ablation of PDK1 led to impaired phosphorylation of AKT and defective activation of mTORC1, resulting in substantially reduced expression of Hif1α and p-STAT3. Meanwhile, decreased p-AKT also suppresses mTORC2-associated GSK3β activity in PDK1-deficient Tfh cells. These integrated effects contributed to the dramatical reduced expression of TCF1 and ultimately impaired the Tfh cell differentiation.
    Keywords:  PDK1; T follicular helper cell; Tcf-1; Tfh; differentiation; immunology; inflammation; mouse
  19. Cell. 2021 Feb 18. pii: S0092-8674(21)00012-X. [Epub ahead of print]184(4): 1064-1080.e20
    Hanna RE, Hegde M, Fagre CR, DeWeirdt PC, Sangree AK, Szegletes Z, Griffith A, Feeley MN, Sanson KR, Baidi Y, Koblan LW, Liu DR, Neal JT, Doench JG.
      Understanding the functional consequences of single-nucleotide variants is critical to uncovering the genetic underpinnings of diseases, but technologies to characterize variants are limiting. Here, we leverage CRISPR-Cas9 cytosine base editors in pooled screens to scalably assay variants at endogenous loci in mammalian cells. We benchmark the performance of base editors in positive and negative selection screens, identifying known loss-of-function mutations in BRCA1 and BRCA2 with high precision. To demonstrate the utility of base editor screens to probe small molecule-protein interactions, we screen against BH3 mimetics and PARP inhibitors, identifying point mutations that confer drug sensitivity or resistance. We also create a library of single guide RNAs (sgRNAs) predicted to generate 52,034 ClinVar variants in 3,584 genes and conduct screens in the presence of cellular stressors, identifying loss-of-function variants in numerous DNA damage repair genes. We anticipate that this screening approach will be broadly useful to readily and scalably functionalize genetic variants.
    Keywords:  CRISPR; ClinVar; DNA damage; PARPi; apoptosis; base editing; genetic screens