Biology subjects

Sasaki, J.

Publications and source records attributed to Sasaki, J..

7 recordsLinked to original sources

bioRxiv2026

PLCXD2 preferentially hydrolyzes phosphatidylinositol and supports retinal lipid homeostasis and photoreceptor integrity

PLCXD proteins have been linked to phosphoinositide metabolism for more than a decade, and PLCXD2 activity has been associated with phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] depletion, yet its preferred direct substrate has remained unresolved. Here, cellular lipidomics showed that catalytically active PLCXD2 reduced the major phosphatidylinositol (PI) 38:4 species, with more modest phosphoinositide changes and increased diacylglycerol (DAG) and phosphatidic acid (PA). Using recombinant PLCXD2 and acyl-chain-matched substrates, we found that PLCXD2 hydrolyzed PI substantially more efficiently than PI(4,5)P2 and most other phosphoinositides tested. In Plcxd2-deficient retina, PI abundance was preserved, whereas DAG and PA were reduced without broad changes in major membrane phospholipid classes. PLCXD2 loss was associated with early structural abnormalities at the photoreceptor-bipolar synaptic interface, followed by outer nuclear layer thinning and reduced electroretinographic a-wave responses. These findings identify PLCXD2 as a PI-preferring mammalian PLC and reveal an endogenous role in retinal lipid homeostasis and outer retinal integrity.

biochemistry↗

bioRxiv2026

PITPβ Drives JAK2 V617F-Mediated Myeloproliferative Neoplasms by Promoting PtdIns(3,4)P2-Dependent AKT Hyperactivation

JAK2 is a key regulator of cytokine-mediated proliferative signaling in hematopoietic stem and progenitor cells. Activating mutations, most commonly JAK2 V617F, trigger aberrant cytokine signaling driving the pathogenesis of myeloproliferative neoplasms (MPNs). Phosphatidylinositol transfer proteins (PITPs) facilitate phosphoinositide synthesis by delivering phosphatidylinositol to lipid kinases, though their roles in oncogenic signaling have remained poorly defined. Here we show that PITP{beta} is critical for the development of JAK2V617F-driven MPN in mice. Deleting Pitp{beta} across the hematopoietic system, but not Pitp, prolonged 25-week survival of Jak2V617F mice from 10% to 85%. Loss of Pitp{beta} attenuated disease-associated splenomegaly and curtailed erythroid progenitors expansion both in vivo and in vitro. Mechanistically, PITP{beta} is necessary for AKT hyperactivation in hematopoietic progenitors, while STAT5 and ERK signaling remain unaffected. In alignment with this role, PITP{beta} promotes the production of PtdIns(3,4)P2, a phosphoinositide that sustains aberrant AKT signaling in Jak2V617F progenitors. Pharmacologic inhibition of AKT with the FDA-approved inhibitor capivasertib in Jak2V617F-transplanted mice similarly reduced splenomegaly and erythroid proliferation, mimicking the effects of Pitp{beta} loss. Collectively, these results identify a novel PITP{beta}-PtdIns(3,4)P2 signaling axis that selectively maintains pathological AKT activation in JAK2V617F-driven MPN, revealing a promising therapeutic vulnerability.

cancer biology↗

bioRxiv2024

Control of Golgi- V-ATPase through Sac1-dependent co-regulation of PI(4)P and cholesterol

Sac1 is a conserved phosphoinositide phosphatase, whose loss-of-function compromises cell and organism viability. Here, we employed acute auxin-inducible Sac1 degradation to identify its immediate downstream effectors in human cells. Most of Sac1 was degraded in [~]1 h, paralleled by increased PI(4)P and decreased cholesterol in the trans-Golgi network (TGN) during the following hour, and superseded by Golgi fragmentation, impaired glycosylation, and selective degradation of TGN proteins by [~]4 h. The TGN disintegration resulted from its acute deacidification caused by disassembly of the Golgi V-ATPase. Mechanistically, Sac1 mediated TGN membrane composition maintained an assembly promoting conformation of the V0a2 subunit. Key phenotypes of acute Sac1 degradation were recapitulated in human differentiated trophoblasts, causing processing defects of chorionic gonadotropin, in line with loss-of-function intolerance of the human SACML1 gene. Collectively, our findings reveal that the assembly of the Golgi V-ATPase is controlled by the TGN membrane via Sac1 fuelled lipid exchange.

cell biology↗

bioRxiv2023

Virological characteristics of the SARS-CoV-2 XBB.1.5 variant

Circulation of SARS-CoV-2 Omicron XBB has resulted in the emergence of XBB.1.5, a new Variant of Interest. Our phylogenetic analysis suggests that XBB.1.5 evolved from XBB.1 by acquiring the F486P spike (S) mutation, subsequent to the acquisition of a nonsense mutation in ORF8. Neutralization assays showed similar abilities of immune escape between XBB.1.5 and XBB.1. We determined the structural basis for the interaction between human ACE2 and the S protein of XBB.1.5, showing similar overall structures between the S proteins of XBB.1 and XBB.1.5. The intrinsic pathogenicity of XBB.1.5 in hamsters is lower than that of XBB.1. Importantly, we found that the ORF8 nonsense mutation of XBB.1.5 resulted in impairment of MHC expression. In vivo experiments using recombinant viruses revealed that the XBB.1.5 mutations are involved with reduced virulence of XBB.1.5. Together, these data suggest that the mutations in ORF8 and S could enhance spreading of XBB.1.5 in humans.

microbiology↗

bioRxiv2023

p53 controls the nuclear entry and epigenetic modification of H3.1 by downregulating nuclear phosphatidic acid

Histones are key molecules of epigenetic regulation and inheritance, and are thought to be chaperoned and transported into the nucleus appropriately prior to being integrated into nucleosomes. H3.1 histone is predominantly synthesized and enters the nucleus during the G1/S phase of the cell cycle, as a new component of duplicating nucleosomes. Here we found that p53 is necessary to secure the normal behavior and modification of H3.1 in the nucleus during the G1/S phase, in which p53 increases C-terminal domain nuclear envelope phosphatase 1 (CTDNEP1) levels and decreases enhancer of zeste homolog 2 (EZH2) levels in the H3.1 interactome. In the absence of p53, H3.1 molecules tended to be tethered at or near the nuclear envelope (NE), where they were predominantly trimethylated at lysine 27 (H3K27me3) by EZH2, without forming nucleosomes. This accumulation was likely caused by the high affinity of H3.1 towards phosphatidic acid (PA). p53 reduced nuclear PA levels by increasing levels of CTDNEP1, which activates lipin to convert PA into diacylglycerol. Induction of the TMEM255A gene by p53 linked p53 with CTDNEP1, in which TMEM255A stabilized CTDNEP1. We moreover found that the cytosolic H3 chaperone HSC70 attenuates the H3.1-PA interaction, and our molecular imaging analyses suggested that H3.1 molecules may be anchored around the NE after their nuclear entry. Our results expand our knowledge of p53 function in regulation of the nuclear behavior of H3.1 during the G1/S phase, in which p53 may primarily target nuclear PA and EZH2.

cell biology↗

bioRxiv2022

Virological characteristics of the novel SARS-CoV-2 Omicron variants including BA.2.12.1, BA.4 and BA.5

After the global spread of SARS-CoV-2 Omicron BA.2 lineage, some BA.2-related variants that acquire mutations in the L452 residue of spike protein, such as BA.2.9.1 and BA.2.13 (L452M), BA.2.12.1 (L452Q), and BA.2.11, BA.4 and BA.5 (L452R), emerged in multiple countries. Our statistical analysis showed that the effective reproduction numbers of these L452R/M/Q-bearing BA.2-related Omicron variants are greater than that of the original BA.2. Neutralization experiments revealed that the immunity induced by BA.1 and BA.2 infections is less effective against BA.4/5. Cell culture experiments showed that BA.2.12.1 and BA.4/5 replicate more efficiently in human alveolar epithelial cells than BA.2, and particularly, BA.4/5 is more fusogenic than BA.2. Furthermore, infection experiments using hamsters indicated that BA.4/5 is more pathogenic than BA.2. Altogether, our multiscale investigations suggest that the risk of L452R/M/Q-bearing BA.2-related Omicron variants, particularly BA.4 and BA.5, to global health is potentially greater than that of original BA.2. HighlightsO_LISpike L452R/Q/M mutations increase the effective reproduction number of BA.2 C_LIO_LIBA.4/5 is resistant to the immunity induced by BA.1 and BA.2 infections C_LIO_LIBA.2.12.1 and BA.4/5 more efficiently spread in human lung cells than BA.2 C_LIO_LIBA.4/5 is more pathogenic than BA.2 in hamsters C_LI

microbiology↗

bioRxiv2018

Bacteria-mediated stabilization of a panel of Picornaviruses

Several viruses encounter various bacterial species within the host and in the environment. Despite these close encounters, the effects of bacteria on picornaviruses specifically is not completely understood. Previous work determined that poliovirus (PV), an enteric virus, has enhanced virion stability when exposed to bacteria or bacterial surface polysaccharides such as lipopolysaccharide. Virion stabilization by bacteria may be important for inter-host transmission since a mutant PV with reduced bacterial binding had a fecal-oral transmission defect in mice. Therefore, we investigated whether bacteria broadly enhance stability of picornaviruses from three different genera: Enterovirus (PV and coxsackievirus B3 (CVB3)), Kobuvirus (Aichi virus) and Cardiovirus (Mengo virus). Furthermore, to delineate strain-specific effects, we examined two strains of CVB3 and a PV mutant with enhanced thermal stability. We determined that specific bacterial strains enhance thermal stability of PV and CVB3, while Mengo virus and Aichi virus are stable at high temperatures in the absence of bacteria. Additionally, we determined that bacteria or lipopolysaccharide can stabilize PV, CVB3, Aichi virus, and Mengo virus during exposure to bleach. These effects are likely mediated through direct interactions with bacteria since viruses bound to bacteria in a pull-down assay. Overall, this work reveals shared and distinct effects of bacteria on a panel of picornaviruses.\n\nIMPORTANCERecent studies have shown that bacteria promote infection and stabilization of poliovirus particles, but the breadth of these effects on other members of the Picornaviridae family is unknown. Here, we compared the effect of bacteria on four distinct members of the Picornaviridae family. We found that bacteria reduced inactivation of all of the viruses during bleach treatment, but not all viral strains were stabilized by bacteria during heat treatment. Overall, our data provide insight into how bacteria play differential roles on picornavirus stability.

microbiology↗