bims-pideca Biomed News
on Class IA PI3K signalling in development and cancer
Issue of 2021‒05‒02
fifteen papers selected by
Ralitsa Radostinova Madsen
University College London Cancer Institute

  1. Proc Natl Acad Sci U S A. 2021 May 04. pii: e2102171118. [Epub ahead of print]118(18):
      The role of integrins, in particular αv integrins, in regulating insulin resistance is incompletely understood. We have previously shown that the αvβ5 integrin ligand milk fat globule epidermal growth factor like 8 (MFGE8) regulates cellular uptake of fatty acids. In this work, we evaluated the impact of MFGE8 on glucose homeostasis. We show that acute blockade of the MFGE8/β5 pathway enhances while acute augmentation dampens insulin-stimulated glucose uptake. Moreover, we find that insulin itself induces cell-surface enrichment of MFGE8 in skeletal muscle, which then promotes interaction between the αvβ5 integrin and the insulin receptor leading to dampening of skeletal-muscle insulin receptor signaling. Blockade of the MFGE8/β5 pathway also enhances hepatic insulin sensitivity. Our work identifies an autoregulatory mechanism by which insulin-stimulated signaling through its cognate receptor is terminated through up-regulation of MFGE8 and its consequent interaction with the αvβ5 integrin, thereby establishing a pathway that can potentially be targeted to improve insulin sensitivity.
    Keywords:  MFGE8; insulin receptor; insulin sensitivity; insulin signaling; integrins
  2. Mol Cancer Res. 2021 Apr 30. pii: molcanres.1066.2020. [Epub ahead of print]
      The phosphoinositol-3 kinase (PI3K)-AKT pathway is one of the most mutated in human cancers, predominantly associated with the loss of the signaling antagonist, PTEN, and to lesser extents, with gain-of-function mutations in PIK3CA (encoding PI3K-p110α) and AKT1. In addition, most oncogenic driver pathways activate PI3K/AKT signaling. Nonetheless, drugs targeting PI3K or AKT have fared poorly against solid tumors in clinical trials as monotherapies, yet some have shown efficacy when combined with inhibitors of other oncogenic drivers, such as receptor tyrosine kinases or nuclear hormone receptors. There is growing evidence that AKT isoforms, AKT1, AKT2, and AKT3, have different, often distinct roles in either promoting or suppressing specific parameters of oncogenic progression, yet few if any isoform-preferred substrates have been characterized. This review will describe recent data showing that the differential activation of AKT isoforms is mediated by complex interplays between PTEN, PI3K isoforms and upstream tyrosine kinases, and that the efficacy of PI3K/AKT inhibitors will likely depend on the successful targeting of specific AKT isoforms and their preferred pathways.
  3. Front Neuroanat. 2021 ;15 664695
      Hyperactivation of the mechanistic target of rapamycin complex 1 (mTORC1) due to mutations in genes along the PI3K-mTOR pathway and the GATOR1 complex causes a spectrum of neurodevelopmental disorders (termed mTORopathies) associated with malformation of cortical development and intractable epilepsy. Despite these gene variants' converging impact on mTORC1 activity, emerging findings suggest that these variants contribute to epilepsy through both mTORC1-dependent and -independent mechanisms. Here, we review the literature on in utero electroporation-based animal models of mTORopathies, which recapitulate the brain mosaic pattern of mTORC1 hyperactivity, and compare the effects of distinct PI3K-mTOR pathway and GATOR1 complex gene variants on cortical development and epilepsy. We report the outcomes on cortical pyramidal neuronal placement, morphology, and electrophysiological phenotypes, and discuss some of the converging and diverging mechanisms responsible for these alterations and their contribution to epileptogenesis. We also discuss potential therapeutic strategies for epilepsy, beyond mTORC1 inhibition with rapamycin or everolimus, that could offer personalized medicine based on the gene variant.
    Keywords:  GATOR1 complex; cortical development; epilepsy; focal cortical dysplasia; in utero electroporation; mTOR; neuron migration; tuberous sclerosis complex
  4. Nature. 2021 Apr 28.
      Vascular malformations are considered monogenic disorders that result in dysregulated vessel growth. Cerebral cavernous malformations (CCMs) arise owing to inactivation of the endothelial CCM protein complex required to dampen MEKK3 activity1-4. Environmental factors explain differences in CCM natural history between individuals5, but why single CCMs often exhibit sudden, rapid growth culminating in stroke or seizure is unknown. Here we demonstrate that CCM growth requires increased PI3K-mTOR signalling and loss of CCM function. We identify PIK3CA gain of function (GOF) and CCM loss of function (LOF) somatic mutations in the same cells in a majority of human CCMs. Using mouse models, we show that CCM growth requires both PI3K GOF and CCM LOF in endothelial cells, and that both CCM LOF and increased expression of the transcription factor KLF4, a downstream MEKK3 effector, augment mTOR signalling in endothelial cells. Consistent with these findings, the mTORC1 inhibitor Rapamycin effectively blocks CCM formation in mouse models. We establish a three-hit mechanism analogous to cancer in which aggressive vascular malformations arise through the loss of vascular "suppressor genes" that constrain vessel growth and gain of a vascular "oncogene" that stimulates excess vessel growth. These findings suggest that aggressive CCMs may be treated using clinically approved mTORC1 inhibitors.
  5. Development. 2021 Apr 15. pii: dev197087. [Epub ahead of print]148(8):
      Regeneration after damage requires early signals to trigger the tissue repair machinery. Reactive oxygen species (ROS) act as early signals that are sensed by the MAP3 kinase Ask1, which in turn activates by phosphorylation the MAP kinases p38 and JNK. The sustained or high activation of these kinases can result in apoptosis, whereas short or low activation can promote regeneration. Using the Ask1-dependent regeneration program, we demonstrate in Drosophila wing that PI3K/Akt signaling is necessary for Ask1 to activate p38, but not JNK. In addition, nutrient restriction or mutations that target Ser83 of the Drosophila Ask1 protein, a PI3K/Akt-sensitive residue, block regeneration. However, these effects can be reversed by the ectopic activation of p38, but not of JNK. Our results demonstrate that Ask1 controls the activation of p38 through Ser83, and that the phosphorylation of p38 during regeneration is nutrient sensitive. This mechanism is important for discriminating between p38 and JNK in the cells involved in tissue repair and regenerative growth.
    Keywords:   Drosophila ; Growth; Insulin; Regeneration; Signaling
  6. Sci Adv. 2021 Apr;pii: eabe7359. [Epub ahead of print]7(18):
      Recent findings indicate that mitochondrial respiration regulates blood endothelial cell proliferation; however, its role in differentiating lymphatic endothelial cells (LECs) is unknown. We hypothesized that mitochondria could work as a sensor of LECs' metabolic specific needs by determining their functional requirements according to their differentiation status and local tissue microenvironment. Accordingly, we conditionally deleted the QPC subunit of mitochondrial complex III in differentiating LECs of mouse embryos. Unexpectedly, mutant mice were devoid of a lymphatic vasculature by mid-gestation, a consequence of the specific down-regulation of main LEC fate regulators, particularly Vegfr3, leading to the loss of LEC fate. Mechanistically, this is a result of reduced H3K4me3 and H3K27ac in the genomic locus of key LEC fate controllers (e.g., Vegfr3 and Prox1). Our findings indicate that by sensing the LEC differentiation status and microenvironmental metabolic conditions, mitochondrial complex III regulates the critical Prox1-Vegfr3 feedback loop and, therefore, LEC fate specification and maintenance.
  7. Org Biomol Chem. 2021 Apr 28.
      A simple and straightforward process for the synthesis of rapamycin peptide conjugates in a regio and chemoselective manner was developed. The methodology comprises the tagging of chemoselective functionalities to rapamycin and peptides which enables the conjugation of free peptides, without protecting the functionality of the side chain amino acids, in high yield and purity. From this methodology, we successfully conjugate free peptides containing up to 15 amino acids. Rapamycin is also conjugated to the peptides known for inhibiting the kinase activity of Akt protein. These conjugates act as dual target inhibitors and inhibit the kinase activity of both mTOR and Akt.
  8. Nature. 2021 Apr 28.
      Somatic mutations drive the development of cancer and may contribute to ageing and other diseases1,2. Despite their importance, the difficulty of detecting mutations that are only present in single cells or small clones has limited our knowledge of somatic mutagenesis to a minority of tissues. Here, to overcome these limitations, we developed nanorate sequencing (NanoSeq), a duplex sequencing protocol with error rates of less than five errors per billion base pairs in single DNA molecules from cell populations. This rate is two orders of magnitude lower than typical somatic mutation loads, enabling the study of somatic mutations in any tissue independently of clonality. We used this single-molecule sensitivity to study somatic mutations in non-dividing cells across several tissues, comparing stem cells to differentiated cells and studying mutagenesis in the absence of cell division. Differentiated cells in blood and colon displayed remarkably similar mutation loads and signatures to their corresponding stem cells, despite mature blood cells having undergone considerably more divisions. We then characterized the mutational landscape of post-mitotic neurons and polyclonal smooth muscle, confirming that neurons accumulate somatic mutations at a constant rate throughout life without cell division, with similar rates to mitotically active tissues. Together, our results suggest that mutational processes that are independent of cell division are important contributors to somatic mutagenesis. We anticipate that the ability to reliably detect mutations in single DNA molecules could transform our understanding of somatic mutagenesis and enable non-invasive studies on large-scale cohorts.
  9. Biomolecules. 2021 Apr 02. pii: 531. [Epub ahead of print]11(4):
      Insulin (InsR) and insulin-like growth factor-1 (IGF1R) receptors mediate the metabolic and growth-promoting actions of insulin and IGF1/IGF2, respectively. Evidence accumulated in recent years indicates that, in addition to their typical cell-surface localization pattern and ligand-activated mechanism of action, InsR and IGF1R are present in the cell nucleus of both normal and transformed cells. Nuclear translocation seems to involve interaction with a small, ubiquitin-like modifier protein (SUMO-1), although this modification is not always a prerequisite. Nuclear InsR and IGF1R exhibit a number of biological activities that classically fit within the definition of transcription factors. These nuclear activities include, among others, sequence-specific DNA binding and transcriptional control. Of particular interest, nuclear IGF1R was capable of binding and stimulating its cognate gene promoter. The physiological relevance of this autoregulatory mechanism needs to be further investigated. In addition to its nuclear localization, studies have identified IGF1R in the Golgi apparatus, and this particular distribution correlated with a migratory phenotype. In summary, the newly described roles of InsR and IGF1R as gene regulators, in concert with their atypical pattern of subcellular distribution, add a further layer of complexity to traditional models of cell signaling. Furthermore, and in view of the emerging role of IGF1R as a potential therapeutic target, a better understanding of the mechanisms responsible for nuclear IGF1R transport and identification of IGF1R interactors might help optimize target directed therapies in oncology.
    Keywords:  IGF1 receptor; cancer; cell nucleus; insulin receptor; insulin-like growth factor-1 (IGF1); transcription factors
  10. Cancer Cell. 2021 Apr 19. pii: S1535-6108(21)00211-7. [Epub ahead of print]
  11. Science. 2021 Apr 29. pii: eaay8118. [Epub ahead of print]
      During infection Legionella bacteria translocate a variety of effectors into host cells that modify host cell membrane trafficking for the benefit of the intracellular pathogen. Here we found a self-organizing system consisting of a bacterial phosphoinositide kinase and its opposing phosphatase that formed spatiotemporal patterns, including traveling waves, to remodel host cellular membranes. The Legionella effector MavQ, a phosphatidylinositol (PI) 3-kinase, was targeted to the endoplasmic reticulum (ER). MavQ and the Legionella PI 3-phosphatase SidP, even in the absence of other bacterial components, drove rapid PI 3-phosphate turnover on the ER, spontaneously forming traveling waves that spread along ER subdomains inducing vesicle/tubule budding. Thus, bacteria can exploit a self-organizing membrane-targeting mechanism to hijack host cellular structures for survival.
  12. Apoptosis. 2021 Apr 27.
      Caspase-mediated cleavage of proteins ensures the irreversible commitment of cells to undergo apoptosis, and is thus a hallmark of apoptosis. Rapamycin-insensitive companion of mTOR (rictor) functions primarily as a core and essential component of mTOR complex 2 (mTORC2) to critically regulate cellular homeostasis. However, its role in the regulation of apoptosis is largely unknown. In the current study, we found that rictor was cleaved to generate two small fragments at ~ 50 kD and ~ 130 kD in cells undergoing apoptosis upon treatment with different stimuli such as the death ligand, TRAIL, and the small molecule, AZD9291. This cleavage was abolished when caspases were inhibited and could be reproduced when directly incubating rictor protein and caspase-3 in vitro. Furthermore, the cleavage site of caspase-3 on rictor was mapped at D1244 (VGVD). These findings together robustly demonstrate that rictor is a substrate of caspase-3 and undergoes cleavage during apoptosis. These results add new information for understanding the biology of rictor in the regulation of cell survival and growth.
    Keywords:  Apoptosis; EGFR-TKIs; Rictor; TRAIL
  13. Cell Syst. 2021 Apr 21. pii: S2405-4712(21)00081-8. [Epub ahead of print]12(4): 338-352.e5
      Hit selection from high-throughput assays remains a critical bottleneck in realizing the potential of omic-scale studies in biology. Widely used methods such as setting of cutoffs, prioritizing pathway enrichments, or incorporating predicted network interactions offer divergent solutions yet are associated with critical analytical trade-offs. The specific limitations of these individual approaches and the lack of a systematic way by which to integrate their rankings have contributed to limited overlap in the reported results from comparable genome-wide studies and costly inefficiencies in secondary validation efforts. Using comparative analysis of parallel independent studies as a benchmark, we characterize the specific complementary contributions of each approach and demonstrate an optimal framework to integrate these methods. We describe selection by iterative pathway group and network analysis looping (SIGNAL), an integrated, iterative approach that uses both pathway and network methods to optimize gene prioritization. SIGNAL is accessible as a rapid user-friendly web-based application ( A record of this paper's transparent peer review is included in the Supplemental information.
    Keywords:  bioinformatics; enrichment; genome-wide studies; genomics; high-throughput hit selection; network analysis; pathway analysis; prioritization; software
  14. Trends Genet. 2021 Apr 23. pii: S0168-9525(21)00082-2. [Epub ahead of print]
      Drug discovery is a complex process with high attrition rate: only about half of the compounds in advanced preclinical stages actually enter human trials. Key to these failures is our lack of understanding of human biology and the difficulties in translating our preclinical knowledge into cures. Here, we examine how genetics can be leveraged in drug discovery to understand and alter human biology.
  15. Trends Cell Biol. 2021 Apr 23. pii: S0962-8924(21)00068-4. [Epub ahead of print]
      Mammary stem cells (MaSCs) have been defined by cell surface marker expression and their ability to repopulate a cleared fat pad, a capacity now known to result from reprogramming upon transplantation. Furthermore, lineage-tracing studies have provoked controversy as to whether MaSCs are unipotent or bi/multipotent. Various innovative experimental approaches, including single-cell RNA sequencing (scRNA-Seq), epigenetic analyses, deep tissue and live imaging, and advanced mouse models, have provided new and unexpected insights into stem and progenitor cells; thus, it is now timely to reappraise our concept of the MaSC hierarchy. Here, I highlight misconceptions, suggest definitions of stem and progenitor cells, and propose a way forward in our search for an understanding of MaSCs.
    Keywords:  hierarchy; mammary; progenitor; quiescent; stem