bims-pideca Biomed News
on Class IA PI3K signalling in development and cancer
Issue of 2021‒09‒05
eight papers selected by
Ralitsa Radostinova Madsen
University College London Cancer Institute

  1. Mol Brain. 2021 Aug 30. 14(1): 131
      The phosphatase and tensin homolog (PTEN) protein, encoded by the PTEN gene on chromosome 10, is a negative regulator of the phosphoinositide 3-kinase (PI3K) signaling pathway. Loss of PTEN has been linked to an array of human diseases, including neurodevelopmental disorders such as macrocephaly and autism. However, it remains unknown whether increased dosage of PTEN can lead to human disease. A recent human genetics study identifies chromosome 10 microduplication encompassing PTEN in patients with microcephaly. Here we generated a human brain organoid model of increased PTEN dosage. We showed that mild PTEN overexpression led to reduced neural precursor proliferation, premature neuronal differentiation, and the formation of significantly smaller brain organoids. PTEN overexpression resulted in decreased AKT activation, and treatment of wild-type organoids with an AKT inhibitor recapitulated the reduced brain organoid growth phenotypes. Together, our findings provide functional evidence that PTEN is a dosage-sensitive gene that regulates human neurodevelopment, and that increased PTEN dosage in brain organoids results in microcephaly-like phenotypes.
    Keywords:  AKT; Brain organoids; Human pluripotent stem cells; Microcephaly; Neural precursors; Neurodevelopmental disorder; PTEN
  2. Nat Commun. 2021 Sep 02. 12(1): 5238
      The most common events in breast cancer (BC) involve chromosome arm losses and gains. Here we describe identification of 1089 gene-centric common insertion sites (gCIS) from transposon-based screens in 8 mouse models of BC. Some gCIS are driver-specific, others driver non-specific, and still others associated with tumor histology. Processes affected by driver-specific and histology-specific mutations include well-known cancer pathways. Driver non-specific gCIS target the Mediator complex, Ca++ signaling, Cyclin D turnover, RNA-metabolism among other processes. Most gCIS show single allele disruption and many map to genomic regions showing high-frequency hemizygous loss in human BC. Two gCIS, Nf1 and Trps1, show synthetic haploinsufficient tumor suppressor activity. Many gCIS act on the same pathway responsible for tumor initiation, thereby selecting and sculpting just enough and just right signaling. These data highlight ~1000 genes with predicted conditional haploinsufficient tumor suppressor function and the potential to promote chromosome arm loss in BC.
  3. J Biol Chem. 2021 Aug 27. pii: S0021-9258(21)00929-7. [Epub ahead of print] 101128
      Targeted strategies against specific driver molecules of cancer have brought about many advances in cancer treatment since the early success of the first small molecule inhibitor Gleevec. Today, there are a multitude of targeted therapies approved by the Food and Drug Administration for the treatment of cancer. However, the initial efficacy of virtually every targeted treatment is often reversed by tumor resistance to the inhibitor through acquisition of new mutations in the target molecule, or reprogramming of the epigenome, transcriptome, or kinome of the tumor cells. At the core of this clinical problem lies the assumption that targeted treatments will only be efficacious if the inhibitors are used at their maximum tolerated doses. Such aggressive regimens create strong selective pressure on the evolutionary progression of the tumor, resulting in resistant cells. High-dose single agent treatments activate alternative mechanisms that bypass the inhibitor, while high-dose combinatorial treatments suffer from increased toxicity resulting in treatment cessation. Although there is an arsenal of targeted agents being tested clinically and pre-clinically, identifying the most effective combination treatment plan remains a challenge. In this review, we discuss novel targeted strategies with an emphasis on the recent cross-disciplinary studies demonstrating that it is possible to achieve anti-tumor efficacy without increasing toxicity by adopting low-dose multi-target approaches to treatment of cancer and metastasis.
    Keywords:  cancer therapy; cell signaling; combination therapy; drug resistance; inhibitor; kinase network; mathematical modeling; mitogen-activated protein kinase (MAPK); receptor tyrosine kinases; targeted therapy
  4. Cell Rep Med. 2021 Aug 17. 2(8): 100361
      Hanker et al. reveal that co-occurring missense mutations in the human epidermal growth factor receptor 2 (HER2) and its catalytically inactive homolog HER3 synergize to promote oncogenic signaling by the HER2/HER3 complex.
  5. Cell Rep. 2021 Aug 31. pii: S2211-1247(21)01087-1. [Epub ahead of print]36(9): 109644
      In holometabolous insects, metamorphic timing and body size are controlled by a neuroendocrine axis composed of the ecdysone-producing prothoracic gland (PG) and its presynaptic neurons (PGNs) producing PTTH. Although PTTH/Torso signaling is considered the primary mediator of metamorphic timing, recent studies indicate that other unidentified PGN-derived factors also affect timing. Here, we demonstrate that the receptor tyrosine kinases anaplastic lymphoma kinase (Alk) and PDGF and VEGF receptor-related (Pvr), function in coordination with PTTH/Torso signaling to regulate pupariation timing and body size. Both Alk and Pvr trigger Ras/Erk signaling in the PG to upregulate expression of ecdysone biosynthetic enzymes, while Alk also suppresses autophagy by activating phosphatidylinositol 3-kinase (PI3K)/Akt. The Alk ligand Jelly belly (Jeb) is produced by the PGNs and serves as a second PGN-derived tropic factor, while Pvr activation mainly relies on autocrine signaling by PG-derived Pvf2 and Pvf3. These findings illustrate that a combination of juxtacrine and autocrine signaling regulates metamorphic timing, the defining event of holometabolous development.
    Keywords:  Drosophila; Jak/Stat; PDGF and VEGF receptor-related; Upd; anaplastic lymphoma kinase; metamorphosis; prothoracic gland; prothoracicotropic hormone; receptor tyrosine kinase
  6. Cell. 2021 Sep 02. pii: S0092-8674(21)00947-8. [Epub ahead of print]184(18): 4597-4611
      We explore the utility of bioengineered human tissues-individually or connected into physiological units-for biological research. While much smaller and simpler than their native counterparts, these tissues are complex enough to approximate distinct tissue phenotypes: molecular, structural, and functional. Unlike organoids, which form spontaneously and recapitulate development, "organs-on-a-chip" are engineered to display some specific functions of whole organs. Looking back, we discuss the key developments of this emerging technology. Thinking forward, we focus on the challenges faced to fully establish, validate, and utilize the fidelity of these models for biological research.
  7. J Clin Invest. 2021 Sep 02. pii: 151975. [Epub ahead of print]
      Little is known about how cells regulate and integrate distinct biosynthetic pathways governing differentiation and cell division. For B-lineage cells it is widely accepted that activated cells must complete several rounds of mitosis before yielding antibody-secreting plasma cells. However, we report that marginal zone (MZ) B cells, innate-like naïve B cells known to generate plasma cells rapidly in response to blood-borne bacteria, generate functional plasma cells despite cell cycle arrest. Further, short-term Notch2 blockade in vivo reversed division-independent differentiation potential and decreased transcript abundance for numerous mTORC1- and Myc-regulated genes. Myc loss compromised plasma cell differentiation for MZ B cells, and reciprocally induced ectopic mTORC1 signaling in follicular B cells enabled division-independent differentiation and plasma cell-affiliated gene expression. We conclude that ongoing in situ Notch2/mTORC1 signaling in MZ B cells establishes a unique cellular state that enables rapid division-independent plasma cell differentiation.
    Keywords:  Adaptive immunity; Cell cycle; Immunoglobulins; Immunology
  8. PLoS Comput Biol. 2021 Aug 30. 17(8): e1009348
      Intra-tumour heterogeneity is a leading cause of treatment failure and disease progression in cancer. While genetic mutations have long been accepted as a primary mechanism of generating this heterogeneity, the role of phenotypic plasticity is becoming increasingly apparent as a driver of intra-tumour heterogeneity. Consequently, understanding the role of this plasticity in treatment resistance and failure is a key component of improving cancer therapy. We develop a mathematical model of stochastic phenotype switching that tracks the evolution of drug-sensitive and drug-tolerant subpopulations to clarify the role of phenotype switching on population growth rates and tumour persistence. By including cytotoxic therapy in the model, we show that, depending on the strategy of the drug-tolerant subpopulation, stochastic phenotype switching can lead to either transient or permanent drug resistance. We study the role of phenotypic heterogeneity in a drug-resistant, genetically homogeneous population of non-small cell lung cancer cells to derive a rational treatment schedule that drives population extinction and avoids competitive release of the drug-tolerant sub-population. This model-informed therapeutic schedule results in increased treatment efficacy when compared against periodic therapy, and, most importantly, sustained tumour decay without the development of resistance.