Abl Family Tyrosine Kinases Are Essential for Basement Membrane Integrity and Cortical Lamination in the Cerebellum

The Abl family nonreceptor tyrosine kinases, consisting of closely related Abl and Arg (Abl-related gene), play essential roles in mouse neurulation, but their functions in the subsequent development of CNS are poorly understood. Here, we show that conditional deletion of Abl in precursors of neurons and glia on an Arg knock-out background leads to striking cerebellar malformations, including defects in anterior cerebellar morphogenesis, granule cell ectopia, and hypoplasia. Time course analyses reveal that the abnormal anterior cerebellar foliation results from local disruptions of the basement membrane (BM) located between radial glial endfeet and the meninges during embryonic cerebellar development. Granule cell ectopia and hypoplasia are also associated with the breaches in the BM and abnormal Bergmann glial networks during postnatal cerebellar development. In vitro culture experiments indicate that Abl/Arg-deficient granule cells can interact with glial processes and proliferate normally in response to sonic hedgehog compared to cells isolated from control mice. Consistent with these findings, selective ablation of Abl family kinases in cerebellar granule cells alone does not cause any abnormality, suggesting that deletion of Abl/Arg from glia is likely required for the mutant phenotype. Together, these results provide compelling evidence that Abl and Arg play key redundant roles in BM maintenance and cortical lamination in the cerebellum

Dissociation of EphB2 Signaling Pathways Mediating Progenitor Cell Proliferation and Tumor Suppression

SummarySignaling proteins driving the proliferation of stem and progenitor cells are often encoded by proto-oncogenes. EphB receptors represent a rare exception; they promote cell proliferation in the intestinal epithelium and function as tumor suppressors by controlling cell migration and inhibiting invasive growth. We show that cell migration and proliferation are controlled independently by the receptor EphB2. EphB2 regulated cell positioning is kinase-independent and mediated via phosphatidylinositol 3-kinase, whereas EphB2 tyrosine kinase activity regulates cell proliferation through an Abl-cyclin D1 pathway. Cyclin D1 regulation becomes uncoupled from EphB signaling during the progression from adenoma to colon carcinoma in humans, allowing continued proliferation with invasive growth. The dissociation of EphB2 signaling pathways enables the selective inhibition of the mitogenic effect without affecting the tumor suppressor function and identifies a pharmacological strategy to suppress adenoma growth

Validation of Drug Like Inhibitors for the New Proton Activated Chloride Channel

PAC, proton-activated chloride channel, is an evolutionarily conserved membrane channel that is activated by extracellular acidification. The molecular identity of PAC is recently cloned, opening the door for further investigations on the channel. Emerging evidence showed that PAC was involved in acid induced cell death, and that mice without the PAC channel showed better recovery after an ischemic stroke model. Yet, pharmacological tools that specifically inhibit PAC are lacking. To overcome this limitation and potentially provide treatment for acidosis related diseases, a high-throughput screening was performed and more than 2000 FDA (Food and Drug Administration) proved drugs were screened and repurposed as potential inhibitors of PAC. During this experiment, the top three drugs found in the screening, Resveratrol, Neostigmine Bromide and 3-Formyl Rifamycin were tested as PAC inhibitors. It has been hypothesized that those three drugs should inhibit acidic induced PAC current. Whole-cell patch clamp experiment was conducted in HEK293 cells to confirm their inhibition on PAC. HEK293 cells were perfused with acidic solution to evoke PAC, and inhibitors were applied together with acidic solution after PAC reached complete opening. The reduction of currents were recorded and compared after the application of inhibitors. 20uM Resveratrol showed 32% inhibition on PAC, while 20uM Neostigmine Bromide showed 50% inhibition and 20uM 3-Formyl Rifamycin showed 52% inhibition when perfusing with pH=4.6 solutions. Our studies suggest that all three drugs showed significant inhibition of PAC channel activity, providing promising pharmacological means to manipulate PAC in vivo

Piezo1, a mechanically activated ion channel, is required for vascular development in mice

Mechanosensation is perhaps the last sensory modality not understood at the molecular level. Ion channels that sense mechanical force are postulated to play critical roles in a variety of biological processes including sensing touch/pain (somatosensation), sound (hearing), and shear stress (cardiovascular physiology); however, the identity of these ion channels has remained elusive. We previously identified Piezo1 and Piezo2 as mechanically activated cation channels that are expressed in many mechanosensitive cell types. Here, we show that Piezo1 is expressed in endothelial cells of developing blood vessels in mice. Piezo1-deficient embryos die at midgestation with defects in vascular remodeling, a process critically influenced by blood flow. We demonstrate that Piezo1 is activated by shear stress, the major type of mechanical force experienced by endothelial cells in response to blood flow. Furthermore, loss of Piezo1 in endothelial cells leads to deficits in stress fiber and cellular orientation in response to shear stress, linking Piezo1 mechanotransduction to regulation of cell morphology. These findings highlight an essential role of mammalian Piezo1 in vascular development during embryonic development

Inhibition of the proton-activated chloride channel PAC by PIP2

Proton-activated chloride (PAC) channel is a ubiquitously expressed pH-sensing ion channel, encoded by PACC1 (TMEM206). PAC regulates endosomal acidification and macropinosome shrinkage by releasing chloride from the organelle lumens. It is also found at the cell surface, where it is activated under pathological conditions related to acidosis and contributes to acid-induced cell death. However, the pharmacology of the PAC channel is poorly understood. Here, we report that phosphatidylinositol (4,5)-bisphosphate (PIP2) potently inhibits PAC channel activity. We solved the cryo-electron microscopy structure of PAC with PIP2 at pH 4.0 and identified its putative binding site, which, surprisingly, locates on the extracellular side of the transmembrane domain (TMD). While the overall conformation resembles the previously resolved PAC structure in the desensitized state, the TMD undergoes remodeling upon PIP2-binding. Structural and electrophysiological analyses suggest that PIP2 inhibits the PAC channel by stabilizing the channel in a desensitized-like conformation. Our findings identify PIP2 as a new pharmacological tool for the PAC channel and lay the foundation for future drug discovery targeting this channel

Replicase Genes of Murine Coronavirus Strains A59 and JHM Are Interchangeable: Differences in Pathogenesis Map to the 3′ One-Third of the Genome

The important roles of the spike protein and other structural proteins in murine coronavirus (MHV) pathogenesis have been demonstrated; however, the role of the replicase gene remains unexplored. We assessed the influence of the replicase genes of the highly neurovirulent MHV-JHM strain and the hepatotropic and mildly neurovirulent A59 strain in acute infection of the mouse. Analysis of chimeric A59/JHM recombinant viruses indicates that the replicase genes are interchangeable and that it is the 3′ end of the genome, encoding the structural proteins, rather than the replicase gene, that determines the pathogenic properties of these chimeras

Endosomal Proteolysis by Cathepsins Is Necessary for Murine Coronavirus Mouse Hepatitis Virus Type 2 Spike-Mediated Entry

Most strains of murine coronavirus mouse hepatitis virus (MHV) express a cleavable spike glycoprotein that mediates viral entry and pH-independent cell-cell fusion. The MHV type 2 (MHV-2) strain of murine coronavirus differs from other strains in that it expresses an uncleaved spike and cannot induce cell-cell fusion at neutral pH values. We show here that while infection of the prototype MHV-A59 strain is not sensitive to pretreatment with lysosomotropic agents, MHV-2 replication is significantly inhibited by these agents. By use of an A59/MHV-2 chimeric virus, the susceptibility to lysosomotropic agents is mapped to the MHV-2 spike, suggesting a requirement of acidification of endosomes for MHV-2 spike-mediated entry. However, acidification is likely not a direct trigger for MHV-2 spike-mediated membrane fusion, as low-pH treatment is unable to overcome ammonium chloride inhibition, and it also cannot induce cell-cell fusion between MHV-2-infected cells. In contrast, trypsin treatment can both overcome ammonium chloride inhibition and promote cell-cell fusion. Inhibitors of the endosomal cysteine proteases cathepsin B and cathepsin L greatly reduce MHV-2 spike-mediated entry, while they have little effect on A59 entry, suggesting that there is a proteolytic step in MHV-2 entry. Finally, a recombinant virus expressing a cleaved MHV-2 spike has the ability to induce cell-cell fusion at neutral pH values and does not require low pH and endosomal cathepsins during infection. These studies demonstrate that endosomal proteolysis by cathepsins is necessary for MHV-2 spike-mediated entry; this is similar to the entry pathway recently described for severe acute respiratory syndrome coronavirus and indicates that coronaviruses may use multiple pathways for entry

Piezo1, a mechanically activated ion channel, is required for vascular development in mice.

Mechanosensation is perhaps the last sensory modality not understood at the molecular level. Ion channels that sense mechanical force are postulated to play critical roles in a variety of biological processes including sensing touch/pain (somatosensation), sound (hearing), and shear stress (cardiovascular physiology); however, the identity of these ion channels has remained elusive. We previously identified Piezo1 and Piezo2 as mechanically activated cation channels that are expressed in many mechanosensitive cell types. Here, we show that Piezo1 is expressed in endothelial cells of developing blood vessels in mice. Piezo1-deficient embryos die at midgestation with defects in vascular remodeling, a process critically influenced by blood flow. We demonstrate that Piezo1 is activated by shear stress, the major type of mechanical force experienced by endothelial cells in response to blood flow. Furthermore, loss of Piezo1 in endothelial cells leads to deficits in stress fiber and cellular orientation in response to shear stress, linking Piezo1 mechanotransduction to regulation of cell morphology. These findings highlight an essential role of mammalian Piezo1 in vascular development during embryonic development

Piezo1, a mechanically activated ion channel, is required for vascular development in mice.

Mechanosensation is perhaps the last sensory modality not understood at the molecular level. Ion channels that sense mechanical force are postulated to play critical roles in a variety of biological processes including sensing touch/pain (somatosensation), sound (hearing), and shear stress (cardiovascular physiology); however, the identity of these ion channels has remained elusive. We previously identified Piezo1 and Piezo2 as mechanically activated cation channels that are expressed in many mechanosensitive cell types. Here, we show that Piezo1 is expressed in endothelial cells of developing blood vessels in mice. Piezo1-deficient embryos die at midgestation with defects in vascular remodeling, a process critically influenced by blood flow. We demonstrate that Piezo1 is activated by shear stress, the major type of mechanical force experienced by endothelial cells in response to blood flow. Furthermore, loss of Piezo1 in endothelial cells leads to deficits in stress fiber and cellular orientation in response to shear stress, linking Piezo1 mechanotransduction to regulation of cell morphology. These findings highlight an essential role of mammalian Piezo1 in vascular development during embryonic development

CRISPR-Cas9 Screens Identify the RNA Helicase DDX3X as a Repressor of C9ORF72 (GGGGCC)n Repeat-Associated Non-AUG Translation

Hexanucleotide GGGGCC repeat expansion in C9ORF72 is the most prevalent genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). One pathogenic mechanism is the aberrant accumulation of dipeptide repeat (DPR) proteins produced by the unconventional translation of expanded RNA repeats. Here, we performed genome-wide CRISPR-Cas9 screens for modifiers of DPR protein production in human cells. We found that DDX3X, an RNA helicase, suppresses the repeat-associated non-AUG translation of GGGGCC repeats. DDX3X directly binds to (GGGGCC)n RNAs but not antisense (CCCCGG)n RNAs. Its helicase activity is essential for the translation repression. Reduction of DDX3X increases DPR levels in C9ORF72-ALS/FTD patient cells and enhances (GGGGCC)n-mediated toxicity in Drosophila. Elevating DDX3X expression is sufficient to decrease DPR levels, rescue nucleocytoplasmic transport abnormalities, and improve survival of patient iPSC-differentiated neurons. This work identifies genetic modifiers of DPR protein production and provides potential therapeutic targets for C9ORF72-ALS/FTD