bims-pideca Biomed News
on Class IA PI3K signalling in development and cancer
Issue of 2020‒01‒12
27 papers selected by
Ralitsa Radostinova Madsen
University College London Cancer Institute

  1. Sci Signal. 2020 Jan 07. pii: eaay2940. [Epub ahead of print]13(613):
      Specificity in signal transduction is determined by the ability of cells to "encode" and subsequently "decode" different environmental signals. Akin to computer software, this "signaling code" governs context-dependent execution of cellular programs through modulation of signaling dynamics and can be corrupted by disease-causing mutations. Class IA phosphoinositide 3-kinase (PI3K) signaling is critical for normal growth and development and is dysregulated in human disorders such as benign overgrowth syndromes, cancer, primary immune deficiency, and metabolic syndrome. Despite decades of PI3K research, understanding of context-dependent regulation of the PI3K pathway and of the underlying signaling code remains rudimentary. Here, we review current knowledge on context-specific PI3K signaling and how technological advances now make it possible to move from a qualitative to quantitative understanding of this pathway. Insight into how cellular PI3K signaling is encoded or decoded may open new avenues for rational pharmacological targeting of PI3K-associated diseases. The principles of PI3K context-dependent signal encoding and decoding described here are likely applicable to most, if not all, major cell signaling pathways.
  2. J Biol Chem. 2020 Jan 08. pii: jbc.RA119.010857. [Epub ahead of print]
      Sestrins represent a family of stress-inducible proteins that prevent the progression of many age- and obesity-associated disorders. Endogenous Sestrins maintain insulin-dependent AKT Ser/Thr kinase (AKT) activation during high-fat diet (HFD)-induced obesity, and overexpressed Sestrins activate AKT in various cell types, including liver and skeletal muscle cells. Although Sestrin-mediated AKT activation improves metabolic parameters, the mechanistic details underlying such improvement remain elusive. Here, we investigated how Sestrin2, the Sestrin homolog highly expressed in liver, induces strong AKT activation. We found that two known targets of Sestrin2, mTOR complex 1 (mTORC1) and AMP-activated protein kinase (AMPK), are not required for Sestrin2-induced AKT activation. Rather, phosphoinositol-3-kinase (PI3K) and mTORC2, kinases upstream of AKT, were essential for Sestrin2-induced AKT activation. Among these kinases, mTORC2 catalytic activity was strongly upregulated upon Sestrin2 overexpression in an in vitro kinase assay, indicating that mTORC2 may represent the major link between Sestrin2 and AKT. As reported previously, Sestrin2 interacted with mTORC2; however, we found here that this interaction occurs indirectly through GATOR2, a pentameric protein complex that directly interacts with Sestrin2. Deleting or silencing WD repeat domain 24 (WDR24), the GATOR2 component essential for the Sestrin2-GATOR2 interaction, or WDR59, the GATOR2 component essential for the GATOR2-mTORC2 interaction, completely ablated Sestrin2-induced AKT activation. We also noted that Sestrin2 also directly binds to the pleckstrin homology (PH) domain of AKT and induces AKT translocation to the plasma membrane. These results uncover a signaling mechanism whereby Sestrin2 activates AKT through GATOR2 and mTORC2.
    Keywords:  Akt PKB; insulin resistance; liver metabolism; mTOR complex (mTORC); signal transduction
  3. Commun Biol. 2019 Aug 23. 2(1): 318
      Knockout of phosphatase and tensin homolog (PTEN-/-) is neuroprotective and promotes axon regeneration in mature neurons. Elevation of mTOR activity in injured neurons has been proposed as the primary underlying mechanism. Here we demonstrate that PTEN-/- also abrogates the inhibitory activity of GSK3 on collapsin response mediator protein 2 (CRMP2) in retinal ganglion cell (RGC) axons. Moreover, maintenance of GSK3 activity in Gsk3S/A knockin mice significantly compromised PTEN-/--mediated optic nerve regeneration as well as the activity of CRMP2, and to a lesser extent, mTOR. These GSK3S/A mediated negative effects on regeneration were rescued by viral expression of constitutively active CRMP2T/A, despite decreased mTOR activation. Gsk3S/A knockin or CRMP2 inhibition also decreased PTEN-/- mediated neurite growth of RGCs in culture and disinhibition towards CNS myelin. Thus, the GSK3/CRMP2 pathway is essential for PTEN-/- mediated axon regeneration. These new mechanistic insights may help to find novel strategies to promote axon regeneration.
  4. Commun Biol. 2019 Aug 06. 2(1): 292
      Receptor activator of nuclear factor (NF)-κB (RANK) signaling promotes pregnancy-dependent epithelial cell differentiation and expansion for mammary gland development, which requires NF-κB pathway-dependent Cyclin D1 induction and inhibitor of DNA binding 2 (Id2) pathway-dependent anti-apoptotic gene induction. However, the roles of tumor necrosis factor receptor-associated factor 6 (TRAF6) remain unclear despite its requirement in RANK signaling. Here we show that TRAF6 is crucial for both mammary stem cell maintenance and pregnancy-induced epithelial cell expansion. TRAF6 deficiency impairs phosphoinositide 3-kinase (PI3K)/AKT and canonical NF-κB pathways, whereas noncanonical NF-κB signaling remains functional. Therefore, we propose that TRAF6 promotes cell proliferation by activating PI3K/AKT signaling to induce retinoblastoma phosphorylation in concert with noncanonical NF-κB pathway-dependent Cyclin D1 induction. Furthermore, TRAF6 inhibits apoptosis by activating canonical NF-κB signaling to induce anti-apoptotic genes with the Id2 pathway. Therefore, proper orchestration of TRAF6-dependent and -independent RANK signals likely establishes mammary gland formation.
  5. Nat Commun. 2020 Jan 10. 11(1): 180
      Macropinocytosis is an evolutionarily-conserved, large-scale, fluid-phase form of endocytosis that has been ascribed different functions including antigen presentation in macrophages and dendritic cells, regulation of receptor density in neurons, and regulation of tumor growth under nutrient-limiting conditions. However, whether macropinocytosis regulates the expansion of non-transformed mammalian cells is unknown. Here we show that primary mouse and human T cells engage in macropinocytosis that increases in magnitude upon T cell activation to support T cell growth even under amino acid (AA) replete conditions. Mechanistically, macropinocytosis in T cells provides access of extracellular AA to an endolysosomal compartment to sustain activation of the mechanistic target of rapamycin complex 1 (mTORC1) that promotes T cell growth. Our results thus implicate a function of macropinocytosis in mammalian cell growth beyond Ras-transformed tumor cells via sustained mTORC1 activation.
  6. Mol Autism. 2020 ;11 2
      Background: Tuberous sclerosis complex (TSC) is a neurodevelopmental disorder with frequent occurrence of epilepsy, autism spectrum disorder (ASD), intellectual disability (ID), and tumors in multiple organs. The aberrant activation of mTORC1 in TSC has led to treatment with mTORC1 inhibitor rapamycin as a lifelong therapy for tumors, but TSC-associated neurocognitive manifestations remain unaffected by rapamycin.Methods: Here, we generated patient-specific, induced pluripotent stem cells (iPSCs) from a TSC patient with a heterozygous, germline, nonsense mutation in exon 15 of TSC1 and established an isogenic set of heterozygous (Het), null and corrected wildtype (Corr-WT) iPSCs using CRISPR/Cas9-mediated gene editing. We differentiated these iPSCs into neural progenitor cells (NPCs) and examined neurodevelopmental phenotypes, signaling and changes in gene expression by RNA-seq.
    Results: Differentiated NPCs revealed enlarged cell size in TSC1-Het and Null NPCs, consistent with mTORC1 activation. TSC1-Het and Null NPCs also revealed enhanced proliferation and altered neurite outgrowth in a genotype-dependent manner, which was not reversed by rapamycin. Transcriptome analyses of TSC1-NPCs revealed differentially expressed genes that display a genotype-dependent linear response, i.e., genes upregulated/downregulated in Het were further increased/decreased in Null. In particular, genes linked to ASD, epilepsy, and ID were significantly upregulated or downregulated warranting further investigation. In TSC1-Het and Null NPCs, we also observed basal activation of ERK1/2, which was further activated upon rapamycin treatment. Rapamycin also increased MNK1/2-eIF4E signaling in TSC1-deficient NPCs.
    Conclusion: MEK-ERK and MNK-eIF4E pathways regulate protein translation, and our results suggest that aberrant translation distinct in TSC1/2-deficient NPCs could play a role in neurodevelopmental defects. Our data showing upregulation of these signaling pathways by rapamycin support a strategy to combine a MEK or a MNK inhibitor with rapamycin that may be superior for TSC-associated CNS defects. Importantly, our generation of isogenic sets of NPCs from TSC patients provides a valuable platform for translatome and large-scale drug screening studies. Overall, our studies further support the notion that early developmental events such as NPC proliferation and initial process formation, such as neurite number and length that occur prior to neuronal differentiation, represent primary events in neurogenesis critical to disease pathogenesis of neurodevelopmental disorders such as ASD.
    Keywords:  CRISPR/Cas9; Disease modeling; Early neurodevelopment; Induced pluripotent stem cells; MEK-ERK1/2; MNK1/2-eIF4E; Neural progenitor cells; TSC1; Tuberous sclerosis complex; mTORC1
  7. Commun Biol. 2019 Nov 14. 2(1): 414
      Malignant cells reconfigure their metabolism to support oncogenic processes such as accelerated growth and proliferation. The mechanisms by which this occurs likely involve alterations to genes that encode metabolic enzymes. Here, using genomics data for 10,528 tumours of 32 different cancer types, we characterise the alterations of genes involved in various metabolic pathways. We find that mutations and copy number variations of metabolic genes are pervasive across all human cancers. Based on the frequencies of metabolic gene alterations, we further find that there are two distinct cancer supertypes that tend to be associated with different clinical outcomes. By utilising the known dose-response profiles of 825 cancer cell lines, we infer that cancers belonging to these supertypes are likely to respond differently to various anticancer drugs. Collectively our analyses define the foundational metabolic features of different cancer supertypes and subtypes upon which discriminatory strategies for treating particular tumours could be constructed.
  8. FASEB J. 2019 Dec 23.
      PPM1A and PTEN emerged as novel suppressors of chronic kidney disease (CKD). Since loss of PPM1A and PTEN in the tubulointerstitium promotes fibrogenesis, defining molecular events underlying PPM1A/PTEN deregulation is necessary to develop expression rescue as novel therapeutic strategies. Here we identify TGF-β1 as a principle repressor of PPM1A, as conditional renal tubular-specific induction of TGF-β1 in mice dramatically downregulates kidney PPM1A expression. TGF-β1 similarly attenuates PPM1A and PTEN expression in human renal epithelial cells and fibroblasts, via a protein degradation mechanism by promoting their ubiquitination. A proteasome inhibitor MG132 rescues PPM1A and PTEN expression, even in the presence of TGF-β1, along with decreased fibrogenesis. Restoration of PPM1A or PTEN similarly limits SMAD3 phosphorylation and the activation of TGF-β1-induced fibrotic genes. Concurrent loss of PPM1A and PTEN levels in aristolochic acid nephropathy further suggests crosstalk between these repressors. PPM1A silencing in renal fibroblasts, moreover, results in PTEN loss, while PTEN stable depletion decreases PPM1A expression with acquisition of a fibroproliferative phenotype in each case. Transient PPM1A expression, conversely, elevates cellular PTEN levels while lentiviral PTEN introduction increases PPM1A expression. PPM1A and PTEN, therefore, co-regulate each other's relative abundance, identifying a previously unknown pathological link between TGF-β1 repressors, contributing to CKD.
    Keywords:  CCN2/CTGF; CKD; PAI-1; TGF-β1; epithelial dysfunction
  9. Cancers (Basel). 2019 Dec 30. pii: E93. [Epub ahead of print]12(1):
      Phosphoinositide kinases (PIKs) are a group of lipid kinases that are important upstream activators of various significant signaling pathways. Hyperactivation of the PI3K/AKT/mTOR pathways-either via mutations or genomic amplification-confers key oncogenic activity, essential for the development and progression of several solid tumors. Alterations in the PIK3CA gene are associated with poor prognosis of solid malignancies. Although the literature reports contradictory prognostic values of PIK3CA in aggressive cancers, most of the available data highlight the important role of PIK3CA mutation in mediating tumorigenesis via increased signaling of the PI3K/AKT/mTOR survival pathway. Several inhibitors of PI3K/AKT/mTOR pathways are investigated as potential therapeutic options in solid malignancies. This article reviews the role of PIK3CA mutations and inhibitors of PI3K/AKT/mTOR pathways in major cancer types and examines its association with clinicopathological parameters and prognosis.
    Keywords:  PI3K/AKT/mTOR pathway; PIK3CA; mutation; overall survival; solid malignancy
  10. PLoS One. 2020 ;15(1): e0227340
      The PI3K/Akt pathway is interconnected to protein kinase CK2, which directly phosphorylates Akt1 at S129. We have previously found that, in HK-2 renal cells, downregulation of the CK2 regulatory subunit β (shCK2β cells) reduces S129 Akt phosphorylation. Here, we investigated in more details how the different CK2 isoforms impact on Akt and other signaling pathways. We found that all CK2 isoforms phosphorylate S129 in vitro, independently of CK2β. However, in HK-2 cells the dependence on CK2β was confirmed by rescue experiments (CK2β re-expression in shCK2β HK-2 cells), suggesting the presence of additional components that drive Akt recognition by CK2 in cells. We also found that CK2β downregulation altered the phosphorylation ratio between the two canonical Akt activation sites (pT308 strongly reduced, pS473 slightly increased) in HK-2 cells. Similar results were found in other cell lines where CK2β was stably knocked out by CRISPR-Cas9 technology. The phosphorylation of rpS6 S235/S236, a downstream effector of Akt, was strongly reduced in shCK2β HK-2 cells, while the phosphorylation of two Akt direct targets, PRAS40 T246 and GSK3β S9, was increased. Differently to what observed in response to CK2β down-regulation, the chemical inhibition of CK2 activity by cell treatment with the specific inhibitor CX-4945 reduced both the Akt canonical sites, pT308 and pS473. In CX-4945-treated cells, the changes in rpS6 pS235/S236 and GSK3β pS9 mirrored those induced by CK2β knock-down (reduction and slight increase, respectively); on the contrary, the effect on PRAS40 pT246 phosphorylation was sharply different, being strongly reduced by CK2 inhibition; this suggests that this Akt target might be dependent on Akt pS473 status in HK-2 cells. Since PI3K/Akt and ERK1/2/p90rsk pathways are known to be interconnected and both modulated by CK2, with GSK3β pS9 representing a convergent point, we investigated if ERK1/2/p90rsk signaling was affected by CK2β knock-down and CX-4945 treatment in HK-2 cells. We found that p90rsk was insensitive to any kind of CK2 targeting; therefore, the observation that, similarly, GSK3β pS9 was not reduced by CK2 blockade suggests that GSK3β phosphorylation is mainly under the control of p90rsk in these cells. However, we found that the PI3K inhibitor LY294002 reduced GSK3β pS9, and concomitantly decreased Snail1 levels (a GSK3β target and Epithelial-to-Mesenchymal transition marker). The effects of LY294002 were observed also in CK2β-downregulated cells, suggesting that reducing GSK3β pS9 could be a strategy to control Snail1 levels in any situation where CK2β is defective, as possibly occurring in cancer cells.
  11. FASEB J. 2020 Jan;34(1): 1546-1557
      G protein-coupled receptors (GPCRs) comprise the largest group of membrane receptors in eukaryotic genomes and collectively they regulate nearly all cellular processes. Despite the widely recognized importance of this class of proteins, many GPCRs remain understudied. G protein-coupled receptor 27 (Gpr27) is an orphan GPCR that displays high conservation during vertebrate evolution. Although, GPR27 is known to be expressed in tissues that regulate metabolism including the pancreas, skeletal muscle, and adipose tissue, its functions are poorly characterized. Therefore, to investigate the potential roles of Gpr27 in energy metabolism, we generated a whole body gpr27 knockout zebrafish line. Loss of gpr27 potentiated the elevation in glucose levels induced by pharmacological or nutritional perturbations. We next leveraged a mass spectrometry metabolite profiling platform to identify other potential metabolic functions of Gpr27. Notably, genetic deletion of gpr27 elevated medium-chain acylcarnitines, in particular C6-hexanoylcarnitine, C8-octanoylcarnitine, C9-nonanoylcarnitine, and C10-decanoylcarnitine, lipid species known to be associated with insulin resistance in humans. Concordantly, gpr27 deletion in zebrafish abrogated insulin-dependent Akt phosphorylation and glucose utilization. Finally, loss of gpr27 increased the expression of key enzymes in carnitine shuttle complex, in particular the homolog to the brain-specific isoform of CPT1C which functions as a hypothalamic energy senor. In summary, our findings shed light on the biochemical functions of Gpr27 by illuminating its role in lipid metabolism, insulin signaling, and glucose homeostasis.
    Keywords:  G protein‐coupled receptors; carnitine palmitoyltransferase I; insulin resistance; lipid metabolism; metabolomic profiling
  12. FASEB J. 2020 Jan;34(1): 555-570
      Muscle wasting, or muscle atrophy, can occur with age, injury, and disease; it affects the quality of life and complicates treatment. Insulin-like growth factor 1 (IGF1) is a key positive regulator of muscle mass. The IGF1/Igf1 gene encodes multiple protein isoforms that differ in tissue expression, potency, and function, particularly in cellular proliferation and differentiation, as well as in systemic versus localized signaling. Genome engineering is a novel strategy for increasing gene expression and has the potential to recapitulate the diverse biology seen in IGF1 signaling through the overexpression of multiple IGF1 isoforms. Using a CRISPR-Cas9 gene activation approach, we showed that the expression of multiple IGF1 or Igf1 mRNA variants can be increased in human and mouse skeletal muscle myoblast cell lines using a single-guide RNA (sgRNA). We found increased IGF1 protein levels in the cell culture media and increased cellular phosphorylation of AKT1, the main effector of IGF1 signaling. We also showed that the expression of Class 1 or Class 2 mRNA variants can be selectively increased by changing the sgRNA target location. The expression of multiple IGF1 or Igf1 mRNA transcript variants in human and mouse skeletal muscle myoblasts promoted myotube differentiation and prevented dexamethasone-induced atrophy in myotubes in vitro. Our findings suggest that this novel approach for enhancing IGF1 signaling has potential therapeutic applications for treating skeletal muscle atrophy.
    Keywords:  gene regulation; insulin‐like growth factor 1; muscle atrophy
  13. Nat Commun. 2020 Jan 10. 11(1): 220
      Cancer stem cells (CSCs) may be responsible for treatment resistance, tumor metastasis, and disease recurrence. Here we demonstrate that the Arf1-mediated lipid metabolism sustains cells enriched with CSCs and its ablation induces anti-tumor immune responses in mice. Notably, Arf1 ablation in cancer cells induces mitochondrial defects, endoplasmic-reticulum stress, and the release of damage-associated molecular patterns (DAMPs), which recruit and activate dendritic cells (DCs) at tumor sites. The activated immune system finally elicits antitumor immune surveillance by stimulating T-cell infiltration and activation. Furthermore, TCGA data analysis shows an inverse correlation between Arf1 expression and T-cell infiltration and activation along with patient survival in various human cancers. Our results reveal that Arf1-pathway knockdown not only kills CSCs but also elicits a tumor-specific immune response that converts dying CSCs into a therapeutic vaccine, leading to durable benefits.
  14. Diabetes. 2020 Jan 08. pii: db190713. [Epub ahead of print]
      Diabetic retinopathy is the most common microvascular complication of diabetes, characterized by the formation of fibrovascular membranes that consist of a variety of cells including vascular endothelial cells (ECs). New therapeutic approaches for this diabetic complication are urgently needed. Here, we report that in cultured human retinal microvascular (HRECs) high glucose induced expression of p110δ, which was also expressed in ECs of fibrovascular membranes from diabetic patients. This catalytic subunit of a receptor regulated PI3K isoform δ is known to be highly-enriched in leukocytes. Using genetic and pharmacological approaches, we show that p110δ activity in cultured ECs controls Akt activation, cell proliferation, migration, and tube formation induced by vascular endothelial growth factor, basic fibroblast growth factor, and epidermal growth factor. Using a mouse model of oxygen-induced retinopathy, p110δ inactivation was found to attenuate pathological retinal angiogenesis. p110δ inhibitors have been approved for use in human B-cell malignancies. Our data suggest that antagonizing p110δ constitutes a previously-unappreciated therapeutic opportunity for diabetic retinopathy.
  15. Mol Biol Cell. 2020 Jan 08. mbcE19110662
      Phosphoinositide conversion regulates a diverse array of dynamic membrane events including endocytosis. However, it is not well understood which enzymes are involved in phosphoinositide conversions for receptor endocytosis. We found by siRNA-mediated knockdown that class II PI3K α-isoform (PI3K-C2α), the 5'-phosphatase synaptojanin1 (Synj1), and the 4'-phosphatase INPP4B, but not PI3K-C2β, Synj2 or INPP4A, were required for TGFβ-induced endocytosis of TGFβ receptor. TGFβ induced rapid decreases in PI(4,5)P2 at the plasma membrane (PM) with increases in PI(4)P, followed by increases in PI(3,4)P2, in a TGFβ receptor kinase ALK5-dependent manner. TGFβ induced the recruitment of both synaptojanin1 and PI3K-C2α to the PM with their substantial colocalization. Knockdown of synaptojanin1 abolished TGFβ-induced PI(4,5)P2 decreases and PI(4)P increases. Interestingly, PI3K-C2α knockdown abolished not only TGFβ-induced PI(3,4)P2 increases, but also TGFβ-induced synaptojanin1 recruitment to the PM, PI(4,5)P2 decreases, and PI(4)P increases. Finally, the phosphoinositide conversions were necessary for TGFβ-induced activation of Smad2 and Smad3. These observations demonstrate that the sequential phosphoinositide conversions mediated by Synj1, PI3K-C2α, and INPP4B are essential for TGFβ receptor endocytosis and its signaling. [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text].
  16. FASEB J. 2019 Dec 12.
      Recent studies have demonstrated an essential role for insulin signaling in folliculogenesis as conditional ablation of Igf1r in primary follicles elicits defective follicle-stimulating hormone responsiveness blocking development at the preantral stage. Thus the potential role of insulin action in the periovulatory window and in the corpus luteum is unknown. To examine this, we generated conditional Insr,Igf1r, and double receptor knockout mice driven by Pgr-Cre. These models escape the preantral follicle block and in response to superovulatory gonadotropins exhibit normal distribution of ovarian follicles and corpora lutea. However, single ablation of Igf1r leads to subfertility and mice lacking both receptors are infertile. Double knockout mice have impaired oocyte development and ovulation. While some oocytes are released and fertilized, subsequent embryo development is retarded, and the embryos potentially fail to thrive due to lack of luteal support. In support of this, we found reduced expression of key enzymes in the steroid synthesis pathway and reduced serum progesterone. In addition to metabolic and steroidogenic pathways, RNA-sequencing analysis revealed transcription factor-3 as an important transcription factor downstream of insulin signaling. Collectively, these results highlight the importance of growth factors of the insulin family during two distinct windows of follicular development, ovulation, and luteinization.
    Keywords:  female reproduction; insulin signaling; knockout mouse; ovary
  17. Nature. 2020 Jan;577(7789): 179-189
      A primary goal of human genetics is to identify DNA sequence variants that influence biomedical traits, particularly those related to the onset and progression of human disease. Over the past 25 years, progress in realizing this objective has been transformed by advances in technology, foundational genomic resources and analytical tools, and by access to vast amounts of genotype and phenotype data. Genetic discoveries have substantially improved our understanding of the mechanisms responsible for many rare and common diseases and driven development of novel preventative and therapeutic strategies. Medical innovation will increasingly focus on delivering care tailored to individual patterns of genetic predisposition.
  18. Nat Metab. 2019 Feb;1(2): 189-200
      Adipose tissue possesses the remarkable capacity to control its size and function in response to a variety of internal and external cues, such as nutritional status and temperature. The regulatory circuits of fuel storage and oxidation in white adipocytes and thermogenic adipocytes (brown and beige adipocytes) play a central role in systemic energy homeostasis, whereas dysregulation of the pathways is closely associated with metabolic disorders and adipose tissue malfunction, including obesity, insulin resistance, chronic inflammation, mitochondrial dysfunction, and fibrosis. Recent studies have uncovered new regulatory elements that control the above parameters and provide new mechanistic opportunities to reprogram fat cell fate and function. In this Review, we provide an overview of the current understanding of adipocyte metabolism in physiology and disease and also discuss possible strategies to alter fuel utilization in fat cells to improve metabolic health.
  19. FASEB J. 2020 Jan;34(1): 754-775
      Unlike many epithelial tissues, the corneal epithelium is insulin insensitive, meaning it does not require insulin for glucose uptake. In this study, we show that insulin differentially regulates mitochondrial respiration in two human mucosal epithelial cell types: insulin-insensitive corneal epithelial cells and insulin-sensitive bronchial epithelial cells. In both cell types, insulin blocks glycogen synthase kinase beta (GSK3β) activity. In the corneal epithelium however, insulin selectively regulates PTEN-induced kinase 1 (PINK-1)-mediated mitophagy and mitochondrial accumulation of insulin receptor (INSR). While insulin blocked basal levels of PINK-1-mediated mitophagy in bronchial epithelial cells, mitochondrial trafficking of INSR was not detectable. We further show that in corneal epithelia, INSR interacts with the voltage-dependent anion channel-1 (VDAC1) in mitochondria and that INSR knockdown triggers robust mitochondrial fragmentation, alterations in mitochondrial polarization, and blocks the induction of PINK-1-mediated mitophagy. Collectively, these data demonstrate that INSR interacts with VDAC1 to mediate mitochondrial stability. We also demonstrate unique interactions between VDAC1 and other receptor tyrosine kinases, indicating a novel role for this family of receptors in mitochondria.
    Keywords:  VDAC1; bronchial epithelial cells; corneal epithelial cells; insulin; mitochondria; receptor tyrosine kinases
  20. Nat Commun. 2020 Jan 10. 11(1): 174
      mTORC1 is an important regulator of muscle mass but how it is modulated by oxygen and nutrients is not completely understood. We show that loss of the prolyl hydroxylase domain isoform 1 oxygen sensor in mice (PHD1KO) reduces muscle mass. PHD1KO muscles show impaired mTORC1 activation in response to leucine whereas mTORC1 activation by growth factors or eccentric contractions was preserved. The ability of PHD1 to promote mTORC1 activity is independent of its hydroxylation activity but is caused by decreased protein content of the leucyl tRNA synthetase (LRS) leucine sensor. Mechanistically, PHD1 interacts with and stabilizes LRS. This interaction is promoted during oxygen and amino acid depletion and protects LRS from degradation. Finally, elderly subjects have lower PHD1 levels and LRS activity in muscle from aged versus young human subjects. In conclusion, PHD1 ensures an optimal mTORC1 response to leucine after episodes of metabolic scarcity.
  21. Cancer Res. 2020 Jan 07. pii: canres.1633.2019. [Epub ahead of print]
      Among malignant mesotheliomas (MM) the sarcomatoid subtype is associated with higher chemoresistance and worst survival. Due to its low incidence, there has been little progress in the knowledge of the molecular mechanisms associated with sarcomatoid MM, which might help to define novel therapeutic targets. In this work, we show that loss of PTEN expression is frequent in human sarcomatoid MM and PTEN expression levels are lower in sarcomatoid MM than in the biphasic and epithelioid subtypes. Combined Pten and Trp53 deletion in mouse mesothelium led to non-epithelioid MM development. In Pten;Trp53-null mice developing MM, the Gαi2 coupled receptor subunit activated MEK/ERK and PI3K resulting in aggressive, immune-suppressed tumors. Combined inhibition of MEK and p110β/PI3K reduced mouse tumor cell growth in vitro. Therapeutic inhibition of MEK and p110β/PI3K using Selumetinib (AZD6244, ARRY-142886) and AZD8186, two drugs that are currently in clinical trials, increased the survival of Pten;Trp53-null mice without major toxicity. This drug combination effectively reduced the proliferation of primary cultures of human pleural (Pl) MM, implicating non-epithelioid histology and high vimentin, AKT1/2, and Gαi2 expression levels as predictive markers of response to combined MEK and p110β/PI3K inhibition. Our findings provide a rationale for the use of Selumetinib and AZD8186 in MM patients with sarcomatoid features. This constitutes a novel targeted therapy for a poor prognosis and frequently chemoresistant group of MM patients, for whom therapeutic options are currently lacking.
  22. FASEB J. 2020 Jan;34(1): 148-160
      Deletion of murine Thm1, an intraflagellar transport A (IFT-A) component that mediates ciliary protein trafficking, causes hyperphagia, obesity, and metabolic syndrome. The role of Thm1 or IFT-A in adipogenesis and insulin sensitivity is unknown. Here, we report that Thm1 knockdown in 3T3-L1 pre-adipocytes promotes adipogenesis and enhances insulin sensitivity in vitro. Yet, pre-obese Thm1 conditional knockout mice show systemic insulin resistance. While insulin-induced AKT activation in Thm1 mutant adipose depots and skeletal muscle are similar to those of control littermates, an attenuated insulin response arises in the mutant liver. Insulin treatment of control and Thm1 mutant primary hepatocytes results in similar AKT activation. Moreover, pair-feeding Thm1 conditional knockout mice produces a normal insulin response, both in the liver and systemically. Thus, hyperphagia caused by a cilia defect, induces hepatic insulin resistance via a non-cell autonomous mechanism. In turn, hepatic insulin resistance drives systemic insulin resistance prior to an obese phenotype. These data demonstrate that insulin signaling across cell types is regulated differentially, and that the liver is particularly susceptible to hyperphagia-induced insulin resistance and a critical determinant of systemic insulin resistance.
    Keywords:  adipogenesis; liver; metabolism; mouse model; primary cilia
  23. Mol Metab. 2020 Jan;pii: S2212-8778(19)30936-6. [Epub ahead of print]31 1-13
      OBJECTIVE: An increase in mass and/or brown adipose tissue (BAT) functionality leads to an increase in energy expenditure, which may be beneficial for the prevention and treatment of obesity. Moreover, distinct class I PI3K isoforms can participate in metabolic control as well as in systemic dysfunctions associated with obesity. In this regard, we analyzed in vivo whether the lack of p85α in BAT (BATp85αKO) could modulate the activity and insulin signaling of this tissue, thereby improving diet-induced obesity and its associated metabolic complications.METHODS: We generated BATp85αKO mice using Cre-LoxP technology, specifically deleting p85α in a conditional manner. To characterize this new mouse model, we used mice of 6 and 12 months of age. In addition, BATp85αKO mice were submitted to a high-fat diet (HFD) to challenge BAT functionality.
    RESULTS: Our results suggest that the loss of p85α in BAT improves its thermogenic functionality, high-fat diet-induced adiposity and body weight, insulin resistance, and liver steatosis. The potential mechanisms involved in the improvement of obesity include (1) increased insulin signaling and lower activation of JNK in BAT, (2) enhanced insulin receptor isoform B (IRB) expression and association with IRS-1 in BAT, (3) lower production of proinflammatory cytokines by the adipose organ, (4) increased iWAT browning, and (5) improved liver steatosis.
    CONCLUSIONS: Our results provide new mechanisms involved in the resistance to obesity development, supporting the hypothesis that the gain of BAT activity induced by the lack of p85α has a direct impact on the prevention of diet-induced obesity and its associated metabolic complications.
    Keywords:  Brown adipose tissue; Insulin resistance; Obesity; White adipose tissue; p85α
  24. Front Oncol. 2019 ;9 1373
      Continuous proliferation of tumor cells requires constant adaptations of energy metabolism to rapidly fuel cell growth and division. This energetic adaptation often comprises deregulated glucose uptake and lactate production in the presence of oxygen, a process known as the "Warburg effect." For many years it was thought that the Warburg effect was a result of mitochondrial damage, however, unlike this proposal tumor cell mitochondria maintain their functionality, and is essential for integrating a variety of signals and adapting the metabolic activity of the tumor cell. The mammalian/mechanistic target of rapamycin complex 1 (mTORC1) is a master regulator of numerous cellular processes implicated in proliferation, metabolism, and cell growth. mTORC1 controls cellular metabolism mainly by regulating the translation and transcription of metabolic genes, such as peroxisome proliferator activated receptor γ coactivator-1 α (PGC-1α), sterol regulatory element-binding protein 1/2 (SREBP1/2), and hypoxia inducible factor-1 α (HIF-1α). Interestingly it has been shown that mTORC1 regulates mitochondrial metabolism, thus representing an important regulator in mitochondrial function. Here we present an overview on the role of mTORC1 in the regulation of mitochondrial functions in cancer, considering new evidences showing that mTORC1 regulates the translation of nucleus-encoded mitochondrial mRNAs that result in an increased ATP mitochondrial production. Moreover, we discuss the relationship between mTORC1 and glutaminolysis, as well as mitochondrial metabolites. In addition, mitochondrial fission processes regulated by mTORC1 and its impact on cancer are discussed. Finally, we also review the therapeutic efficacy of mTORC1 inhibitors in cancer treatments, considering its use in combination with other drugs, with particular focus on cellular metabolism inhibitors, that could help improve their anti neoplastic effect and eliminate cancer cells in patients.
    Keywords:  cancer; mTORC1; mitochondria; mitochondrial functions; therapy
  25. Genes Cells. 2020 Jan 11.
      Adipocyte differentiation is accompanied by a pronounced change in the actin cytoskeleton characterized by the reorganization of filamentous (F)-actin stress fibers into cortical F-actin structures. We previously showed that depolymerization of F-actin stress fibers induced by inactivation of RhoA-ROCK (Rho-associated kinase) signaling acts as a trigger for adipocyte differentiation. The relevance and underlying mechanism of the formation of cortical F-actin structures from depolymerized actin during adipocyte differentiation have remained unclear, however. We have now examined the mechanistic relation between actin dynamics and adipogenic induction. Transient exposure to the actin-depolymerizing agent latrunculin A (LatA) supported the formation of adipocyte-associated cortical actin structures and the completion of terminal adipocyte differentiation in the presence of insulin, whereas long-term exposure to LatA prevented such actin reorganization as well as terminal adipogenesis. Moreover, these effects of insulin were prevented by inhibition of phosphatidylinositol 3-kinase (PI3K)-Rac1 signaling and the actin-related protein 2/3 (Arp2/3) complex which is a critical component of the cortical actin networks. Our findings thus suggest that the insulin-PI3K-Rac1 axis leads to the formation of adipocyte-associated cortical actin structures which is an essential for completion of adipocyte differentiation.
    Keywords:  Rac1; actin cytoskeleton; adipocyte differentiation; insulin; phosphatidylinositol 3-kinase (PI3K)
  26. Glia. 2020 Jan 06.
      Oligodendrocyte precursor cells (OPCs) differentiate and mature into oligodendrocytes, which produce myelin in the central nervous system. Prior studies have shown that the mechanistic target of rapamycin (mTOR) is necessary for proper myelination of the mouse spinal cord and that bone morphogenetic protein (BMP) signaling inhibits oligodendrocyte differentiation, in part by promoting expression of inhibitor of DNA binding 2 (Id2). Here we provide evidence that mTOR functions specifically in the transition from early stage OPC to immature oligodendrocyte by downregulating BMP signaling during postnatal spinal cord development. When mTOR is deleted from the oligodendrocyte lineage, expression of the FK506 binding protein 1A (FKBP12), a suppressor of BMP receptor activity, is reduced, downstream Smad activity is increased and Id2 expression is elevated. Additionally, mTOR inhibition with rapamycin in differentiating OPCs alters the transcriptional complex present at the Id2 promoter. Deletion of mTOR in oligodendroglia in vivo resulted in fewer late stage OPCs and fewer newly formed oligodendrocytes in the spinal cord with no effect on OPC proliferation or cell cycle exit. Finally, we demonstrate that inhibiting BMP signaling rescues the rapamycin-induced deficit in myelin protein expression. We conclude that mTOR promotes early oligodendrocyte differentiation by suppressing BMP signaling in OPCs.
    Keywords:  BMP signaling; FKBP12; Id2; OPC; mTOR
  27. Nat Commun. 2020 Jan 09. 11(1): 138
      In C. elegans, the conserved transcription factor DAF-16/FOXO is a powerful aging regulator, relaying dire conditions into expression of stress resistance and longevity promoting genes. For some of these functions, including low insulin/IGF signaling (IIS), DAF-16 depends on the protein SMK-1/SMEK, but how SMK-1 exerts this role has remained unknown. We show that SMK-1 functions as part of a specific Protein Phosphatase 4 complex (PP4SMK-1). Loss of PP4SMK-1 hinders transcriptional initiation at several DAF-16-activated genes, predominantly by impairing RNA polymerase II recruitment to their promoters. Search for the relevant substrate of PP4SMK-1 by phosphoproteomics identified the conserved transcriptional regulator SPT-5/SUPT5H, whose knockdown phenocopies the loss of PP4SMK-1. Phosphoregulation of SPT-5 is known to control transcriptional events such as elongation and termination. Here we also show that transcription initiating events are influenced by the phosphorylation status of SPT-5, particularly at DAF-16 target genes where transcriptional initiation appears rate limiting, rendering PP4SMK-1 crucial for many of DAF-16's physiological roles.