bims-pideca Biomed News
on Class IA PI3K signalling in development and cancer
Issue of 2020‒06‒21
thirteen papers selected by
Ralitsa Radostinova Madsen
University College London Cancer Institute

  1. Cell. 2020 Jun 18. pii: S0092-8674(20)30686-3. [Epub ahead of print]
      Oncogenic transformation is associated with profound changes in cellular metabolism, but whether tracking these can improve disease stratification or influence therapy decision-making is largely unknown. Using the iKnife to sample the aerosol of cauterized specimens, we demonstrate a new mode of real-time diagnosis, coupling metabolic phenotype to mutant PIK3CA genotype. Oncogenic PIK3CA results in an increase in arachidonic acid and a concomitant overproduction of eicosanoids, acting to promote cell proliferation beyond a cell-autonomous manner. Mechanistically, mutant PIK3CA drives a multimodal signaling network involving mTORC2-PKCζ-mediated activation of the calcium-dependent phospholipase A2 (cPLA2). Notably, inhibiting cPLA2 synergizes with fatty acid-free diet to restore immunogenicity and selectively reduce mutant PIK3CA-induced tumorigenicity. Besides highlighting the potential for metabolic phenotyping in stratified medicine, this study reveals an important role for activated PI3K signaling in regulating arachidonic acid metabolism, uncovering a targetable metabolic vulnerability that largely depends on dietary fat restriction.
    Keywords:  PIK3CA; PKCζ; arachidonic acid; cPLA2; cancer metabolism; diet; eicosanoids; fat restriction; iKnife; mTORC2
  2. EMBO Mol Med. 2020 Jun 17. e11674
      Peripheral nervous system (PNS) neurons support axon regeneration into adulthood, whereas central nervous system (CNS) neurons lose regenerative ability after development. To better understand this decline whilst aiming to improve regeneration, we focused on phosphoinositide 3-kinase (PI3K) and its product phosphatidylinositol (3,4,5)-trisphosphate (PIP3 ). We demonstrate that adult PNS neurons utilise two catalytic subunits of PI3K for axon regeneration: p110α and p110δ. However, in the CNS, axonal PIP3 decreases with development at the time when axon transport declines and regenerative competence is lost. Overexpressing p110α in CNS neurons had no effect; however, expression of p110δ restored axonal PIP3 and increased regenerative axon transport. p110δ expression enhanced CNS regeneration in both rat and human neurons and in transgenic mice, functioning in the same way as the hyperactivating H1047R mutation of p110α. Furthermore, viral delivery of p110δ promoted robust regeneration after optic nerve injury. These findings establish a deficit of axonal PIP3 as a key reason for intrinsic regeneration failure and demonstrate that native p110δ facilitates axon regeneration by functioning in a hyperactive fashion.
    Keywords:  CNS axon regeneration; axon transport; optic nerve; p110 delta; phosphoinositide 3-kinase
  3. Nat Cell Biol. 2020 Jun 15.
      Coat proteins have a central role in vesicular transport by binding to cargoes for their sorting into intracellular pathways. Cargo recognition is mediated by components of the coat complex known as adaptor proteins1-3. We previously showed that Arf-GAP with coil-coil, ANK repeat and PH domain-containing protein 1 (ACAP1) functions as an adaptor for a clathrin coat complex that has a function in endocytic recycling4-6. Here, we show that the protein kinase Akt acts as a co-adaptor in this complex, and is needed in conjunction with ACAP1 to bind to cargo proteins to promote their recycling. In addition to advancing the understanding of endocytic recycling, we uncover a fundamentally different function in which a kinase acts, as Akt in this case is an effector rather than a regulator in a cellular event.
  4. Signal Transduct Target Ther. 2019 Jun 19. 4(1): 20
      The phosphatidylinositol 3-kinase (PI3K)-Akt-mechanistic target of rapamycin (mTOR) pathway is constitutively activated in human acute myeloid leukemia (AML) cells and is regarded as a possible therapeutic target. Insulin is an agonist of this pathway and a growth factor for AML cells. We characterized the effect of insulin on the phosphorylation of 10 mediators in the main track of the PI3K-Akt-mTOR pathway in AML cells from 76 consecutive patients. The overall results showed that insulin significantly increased the phosphorylation of all investigated mediators. However, insulin effects on the pathway activation profile varied among patients, and increased phosphorylation in all mediators was observed only in a minority of patients; in other patients, insulin had divergent effects. Global gene expression profiling and proteomic/phosphoproteomic comparisons suggested that AML cells from these two patient subsets differed with regard to AML cell differentiation, transcriptional regulation, RNA metabolism, and cellular metabolism. Strong insulin-induced phosphorylation was associated with weakened antiproliferative effects of metabolic inhibitors. PI3K, Akt, and mTOR inhibitors also caused divergent effects on the overall pathway phosphorylation profile in the presence of insulin, although PI3K and Akt inhibition caused a general reduction in Akt pT308 and 4EBP1 pT36/pT45 phosphorylation. For Akt inhibition, the phosphorylation of upstream mediators was generally increased or unaltered. In contrast, mTOR inhibition reduced mTOR pS2448 and S6 pS244 phosphorylation but increased Akt pT308 phosphorylation. In conclusion, the effects of both insulin and PI3K-Akt-mTOR inhibitors differ between AML patient subsets, and differences in insulin responsiveness are associated with differential susceptibility to metabolic targeting.
  5. Nat Commun. 2020 Jun 19. 11(1): 3148
      Macroautophagy ("autophagy") is the main lysosomal catabolic process that becomes activated under nutrient-depleted conditions, like amino acid (AA) starvation. The mechanistic target of rapamycin complex 1 (mTORC1) is a well-conserved negative regulator of autophagy. While leucine (Leu) is a critical mTORC1 regulator under AA-starved conditions, how Leu regulates autophagy is poorly understood. Here, we describe that in most cell types, including neurons, Leu negatively regulates autophagosome biogenesis via its metabolite, acetyl-coenzyme A (AcCoA). AcCoA inhibits autophagy by enhancing EP300-dependent acetylation of the mTORC1 component raptor, with consequent activation of mTORC1. Interestingly, in Leu deprivation conditions, the dominant effects on autophagy are mediated by decreased raptor acetylation causing mTORC1 inhibition, rather than by altered acetylation of other autophagy regulators. Thus, in most cell types we examined, Leu regulates autophagy via the impact of its metabolite AcCoA on mTORC1, suggesting that AcCoA and EP300 play pivotal roles in cell anabolism and catabolism.
  6. Oncogene. 2020 Jun 15.
      The mammalian target of rapamycin (mTOR) functions as two complexes (mTORC1 and mTORC2), regulating cell growth and metabolism. Aberrant mTOR signaling occurs frequently in cancers, so mTOR has become an attractive target for cancer therapy. Iron chelators have emerged as promising anticancer agents. However, the mechanisms underlying the anticancer action of iron chelation are not fully understood. Particularly, reports on the effects of iron chelation on mTOR complexes are inconsistent or controversial. Here, we found that iron chelators consistently inhibited mTORC1 signaling, which was blocked by pretreatment with ferrous sulfate. Mechanistically, iron chelation-induced mTORC1 inhibition was not related to ROS induction, copper chelation, or PP2A activation. Instead, activation of AMPK pathway mainly and activation of both HIF-1/REDD1 and Bnip3 pathways partially contribute to iron chelation-induced mTORC1 inhibition. Our findings indicate that iron chelation inhibits mTORC1 via multiple pathways and iron is essential for mTORC1 activation.
  7. Mol Cell Proteomics. 2020 Jun 18. pii: mcp.RA120.002069. [Epub ahead of print]
      Insulin receptor substrate 2 (IRS2) is an essential adaptor that mediates signaling downstream of the insulin receptor and other receptor tyrosine kinases. Transduction through IRS2-dependent pathways is important for coordinating metabolic homeostasis, and dysregulation of IRS2 causes systemic insulin signaling defects. Despite the importance of maintaining proper IRS2 abundance, little is known about what factors mediate its protein stability. We conducted an unbiased proteomic screen to uncover novel substrates of the Anaphase Promoting Complex/Cyclosome (APC/C), a ubiquitin ligase that controls the abundance of key cell cycle regulators. We found that IRS2 levels are regulated by APC/C activity and that IRS2 is a direct APC/C target in G1 Consistent with the APC/C's role in degrading cell cycle regulators, quantitative proteomic analysis of IRS2-null cells revealed a deficiency in proteins involved in cell cycle progression. We further show that cells lacking IRS2 display a weakened spindle assembly checkpoint in cells treated with microtubule inhibitors. Together, these findings reveal a new pathway for IRS2 turnover and indicate that IRS2 is a component of the cell cycle control system in addition to acting as an essential metabolic regulator.
    Keywords:  Anaphase Promoting Complex (APC/C); Cell cycle*; Cell division*; Enzyme Inhibition*; G1; Insulin signaling pathway; Mitosis; Ubiquitin
  8. Cell Death Dis. 2020 Jun 15. 11(6): 464
      Nuclear envelope component PRR14 has been detected to be upregulated in varieties of cancers, especially in breast cancer. But its role in breast carcinogenesis is poorly understood. In this study, we show PRR14 contributes to breast carcinogenesis mainly through overexpression, which derives from elevated transcription and gene amplification. Increased PRR14 expression promotes breast cancer cell proliferation and tumor formation. Biochemical analysis reveals, in addition to previously reported activation of PI3-kinase/Akt/mTOR pathway, PRR14 overexpression regulates cell cycle in breast cancer by inhibiting CHEK2's activation, followed with the deregulation of DNA damage pathway. In correspondence, CHEK2 and PRR14 show opposite impact on breast cancer patients receiving chemotherapy. Collectively, our study is the first to document the oncogenetic role of PRR14 in breast cancer, which protects cells from apoptosis and stimulates proliferation by activating the PI3-kinase/Akt/mTOR pathway and inhibiting the CHEK2 pathway. Both of these pathways are of great influence in breast cancer and PRR14 appears to be their novel interacting node, which renders patients more resistance to chemotherapy and provides a potential therapeutic target in breast cancer.
  9. Circ Res. 2020 Jun 17.
      Rationale: We previously identified somatic activating mutations in the KRAS gene in the endothelium of the majority of human sporadic brain arteriovenous malformations (bAVMs); a disorder characterized by direct connections between arteries and veins. However, whether this genetic abnormality alone is sufficient for lesion formation, as well as how active KRAS signaling contributes to AVM formation, remains unknown. Objective:To establish the first in vivo models of somatic KRAS gain of function in the endothelium in both mice and zebrafish in order to directly observe the phenotypic consequences of constitutive KRAS activity at a cellular level in vivo, and to test potential therapeutic interventions for AVMs. Methods and Results: Using both postnatal and adult mice, as well as embryonic zebrafish, we demonstrate that endothelial-specific gain of function mutations in Kras (G12D or G12V) are sufficient to induce bAVMs. Active KRAS signaling leads to altered endothelial cell morphogenesis and increased cell size, ectopic sprouting, expanded vessel lumen diameter, and direct connections between arteries and veins. Furthermore, we show that these lesions are not associated with altered endothelial growth dynamics or a lack of proper arteriovenous identity, but instead appear to feature exuberant angiogenic signaling. Finally, we demonstrate that KRAS-dependent AVMs in zebrafish are refractory to inhibition of the downstream effector PI3K, but instead require active MEK signaling. Conclusions: We demonstrate that active KRAS expression in the endothelium is sufficient for bAVM formation, even in the setting of uninjured adult vasculature. Furthermore, the finding that KRAS-dependent lesions are reversible in zebrafish suggests that MEK inhibition may represent a promising therapeutic treatment for AVM patients.
    Keywords:  angiogenesis; animal model cardiovascular disease; arteriovenous malformations; lumen enlargement; somatic mutation
  10. Sci Signal. 2020 Jun 16. pii: eaay1451. [Epub ahead of print]13(636):
      Despite decades of effort, the sensitivity of patient tumors to individual drugs is often not predictable on the basis of molecular markers alone. Therefore, unbiased, high-throughput approaches to match patient tumors to effective drugs, without requiring a priori molecular hypotheses, are critically needed. Here, we improved upon a method that we previously reported and developed called high-throughput dynamic BH3 profiling (HT-DBP). HT-DBP is a microscopy-based, single-cell resolution assay that enables chemical screens of hundreds to thousands of candidate drugs on freshly isolated tumor cells. The method identifies chemical inducers of mitochondrial apoptotic signaling, a mechanism of cell death. HT-DBP requires only 24 hours of ex vivo culture, which enables a more immediate study of fresh primary tumor cells and minimizes adaptive changes that occur with prolonged ex vivo culture. Effective compounds identified by HT-DBP induced tumor regression in genetically engineered and patient-derived xenograft (PDX) models of breast cancer. We additionally found that chemical vulnerabilities changed as cancer cells expanded ex vivo. Furthermore, using PDX models of colon cancer and resected tumors from colon cancer patients, our data demonstrated that HT-DBP could be used to generate personalized pharmacotypes. Thus, HT-DBP appears to be an ex vivo functional method with sufficient scale to simultaneously function as a companion diagnostic, therapeutic personalization, and discovery tool.
  11. Clin Sci (Lond). 2020 Jun 26. 134(12): 1377-1397
      From the time of first characterization of PI3K as a heterodimer made up of a p110 catalytic subunit and a regulatory subunit, a wealth of evidence have placed the class IA PI3Ks at the forefront of drug development for the treatment of various diseases including cancer. The p110α isoform was quickly brought at the centre of attention in the field of cancer research by the discovery of cancer-specific gain-of-function mutations in PIK3CA gene in a range of human solid tumours. In contrast, p110δ PI3K was placed into the spotlight of immunity, inflammation and haematologic malignancies because of the preferential expression of this isoform in leucocytes and the rare mutations in PIK3CD gene. The last decade, however, several studies have provided evidence showing that the correlation between the PIK3CA mutations and the response to PI3K inhibition is less clear than originally considered, whereas concurrently an unexpected role of p110δ PI3K in solid tumours has being emerging. While PIK3CD is mostly non-mutated in cancer, the expression levels of p110δ protein seem to act as an intrinsic cancer-causing driver in various solid tumours including breast, prostate, colorectal and liver cancer, Merkel-Cell carcinoma, glioblastoma and neurobalstoma. Furthermore, p110δ selective inhibitors are being studied as potential single agent treatments or as combination partners in attempt to improve cancer immunotherapy, with both strategies to shown great promise for the treatment of several solid tumours. In this review, we discuss the evidence implicating the p110δ PI3K in human solid tumours, their impact on the current state of the field and the potential of using p110δ-selective inhibitors as monotherapy or combined therapy in different cancer contexts.
    Keywords:  cancer cells; immune checkpoint molecules; p110d PI3K; solid tumours; tumour microenvironment
  12. Trends Cancer. 2020 Jun 11. pii: S2405-8033(20)30165-5. [Epub ahead of print]
      Chemotherapy is central to oncology, perceived to operate only on prolific cancerous tissue. Yet, many non-neoplastic tissues are more prolific compared with typical tumors. Chemotherapies achieve sufficient therapeutic windows to exert antineoplastic activity because they are prodrugs that are bioactivated in cancer-specific environments. The advent of precision medicine has obscured this concept, favoring the development of high-potency kinase inhibitors. Inhibitors of essential mitotic kinases exemplify this paradigm shift, but intolerable on-target toxicities in more prolific normal tissues have led to repeated failures in the clinic. Proliferation rates alone cannot be used to achieve cancer specificity. Here, we discuss integrating the cancer specificity of prodrugs from classical chemotherapeutics and the potency of mitotic kinase inhibitors to generate a class of high-precision cancer therapeutics.
    Keywords:  cell cycle; chemotherapy; cyclin-dependent kinases; kinesin; precision oncology; pro-drug; targeted therapy
  13. Proc Natl Acad Sci U S A. 2020 Jun 19. pii: 201914167. [Epub ahead of print]
      The mechanisms used by embryos to pattern tissues across their axes has fascinated developmental biologists since the founding of embryology. Here, using single-cell technology, we interrogate complex patterning defects and define a Hedgehog (Hh)-fibroblast growth factor (FGF) signaling axis required for anterior mesoderm lineage development during gastrulation. Single-cell transcriptome analysis of Hh-deficient mesoderm revealed selective deficits in anterior mesoderm populations, culminating in defects to anterior embryonic structures, including the pharyngeal arches, heart, and anterior somites. Transcriptional profiling of Hh-deficient mesoderm during gastrulation revealed disruptions to both transcriptional patterning of the mesoderm and FGF signaling for mesoderm migration. Mesoderm-specific Fgf4/Fgf8 double-mutants recapitulated anterior mesoderm defects and Hh-dependent GLI transcription factors modulated enhancers at FGF gene loci. Cellular migration defects during gastrulation induced by Hh pathway antagonism were mitigated by the addition of FGF4 protein. These findings implicate a multicomponent signaling hierarchy activated by Hh ligands from the embryonic node and executed by FGF signals in nascent mesoderm to control anterior mesoderm patterning.
    Keywords:  FGF signaling; Hedgehog signaling; embryonic node; mesoderm; single-cell sequencing