Assembly of a Fab1 phosphoinositide kinase signaling complex requires the Fig4 phosphoinositide phosphatase.
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ABSTRACT:
SUBMITTER: Botelho RJ
PROVIDER: S-EPMC2555960 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Mutations of the lipid phosphatase FIG4 that regulates PI(3,5)P(2) are responsible for the recessive peripheral-nerve disorder CMT4J. We now describe nonsynonymous variants of FIG4 in 2% (9/473) of patients with amyotrophic lateral sclerosis (ALS) and primary lateral sclerosis (PLS). Heterozygosity for a deleterious allele of FIG4 appears to be a risk factor for ALS and PLS, extending the list of known ALS genes and increasing the clinical spectrum of FIG4-related diseases.
| S-EPMC2668033 | biostudies-literature
Project description:ObjectiveThe aim of this study was to identify the causal gene in a consanguineous Moroccan family with temporo-occipital polymicrogyria, psychiatric manifestations, and epilepsy, previously mapped to the 6q16-q22 region.MethodsWe used exome sequencing and analyzed candidate variants in the 6q16-q22 locus, as well as a rescue assay in Fig4-null mouse fibroblasts and immunohistochemistry of Fig4-null mouse brains.ResultsA homozygous missense mutation (p.Asp783Val) in the phosphoinositide phosphatase gene FIG4 was identified. Pathogenicity of the variant was supported by impaired rescue of the enlarged vacuoles in transfected fibroblasts from Fig4-deficient mice. Histologic examination of Fig4-null mouse brain revealed neurodevelopmental impairment in the hippocampus, cortex, and cerebellum as well as impaired cerebellar gyration/foliation reminiscent of human cortical malformations.ConclusionsThis study extends the spectrum of phenotypes associated with FIG4 mutations to include cortical malformation associated with seizures and psychiatric manifestations, in addition to the previously described Charcot-Marie-Tooth disease type 4J and Yunis-Varón syndrome.
| S-EPMC3962989 | biostudies-literature
Project description:Yunis-Varón syndrome (YVS) is an autosomal-recessive disorder with cleidocranial dysplasia, digital anomalies, and severe neurological involvement. Enlarged vacuoles are found in neurons, muscle, and cartilage. By whole-exome sequencing, we identified frameshift and missense mutations of FIG4 in affected individuals from three unrelated families. FIG4 encodes a phosphoinositide phosphatase required for regulation of PI(3,5)P(2) levels, and thus endosomal trafficking and autophagy. In a functional assay, both missense substitutions failed to correct the vacuolar phenotype of Fig4-null mouse fibroblasts. Homozygous Fig4-null mice exhibit features of YVS, including neurodegeneration and enlarged vacuoles in neurons. We demonstrate that Fig4-null mice also have small skeletons with reduced trabecular bone volume and cortical thickness and that cultured osteoblasts accumulate large vacuoles. Our findings demonstrate that homozygosity or compound heterozygosity for null mutations of FIG4 is responsible for YVS, the most severe known human phenotype caused by defective phosphoinositide metabolism. In contrast, in Charcot-Marie-Tooth disease type 4J (also caused by FIG4 mutations), one of the FIG4 alleles is hypomorphic and disease is limited to the peripheral nervous system. This genotype-phenotype correlation demonstrates that absence of FIG4 activity leads to central nervous system dysfunction and extensive skeletal anomalies. Our results describe a role for PI(3,5)P(2) signaling in skeletal development and maintenance.
| S-EPMC3644641 | biostudies-literature
Project description:Aspergillus flavus (A. flavus) is one of the most important model environmental fungi which can produce a potent toxin and carcinogen known as aflatoxin. Aflatoxin contamination causes massive agricultural economic loss and a critical human health issue each year. Although a functional vacuole has been highlighted for its fundamental importance in fungal virulence, the molecular mechanisms of the vacuole in regulating the virulence of A. flavus remain largely unknown. Here, we identified a novel vacuole-related protein in A. flavus, the ortholog of phosphatidylinositol-3-phosphate-5-kinase (Fab1) in Saccharomyces cerevisiae. This kinase was located at the vacuolar membrane, and loss of fab1 function was found to affect the growth, conidia and sclerotial development, cellular acidification and metal ion homeostasis, aflatoxin production and pathogenicity of A. flavus. Further functional analysis revealed that Fab1 was required to maintain the vacuole size and cell morphology. Additional quantitative proteomic analysis suggested that Fab1 was likely to play an important role in maintaining vacuolar/cellular homeostasis, with vacuolar dysregulation upon fab1 deletion leading to impaired aflatoxin synthesis in this fungus. Together, these results provide insight into the molecular mechanisms by which this pathogen produces aflatoxin and mediates its pathogenicity, and may facilitate dissection of the vacuole-mediated regulatory network in A. flavus.
| S-EPMC7781676 | biostudies-literature
Project description:We previously showed that the herpes simplex virus 1 (HSV-1) tegument protein VP11/12 activates the lymphocyte-specific Src family kinase (SFK) Lck and is tyrosine phosphorylated in an Lck-dependent manner during T cell infection. We now extend these findings to show that ectopic expression of Lck induces robust tyrosine phosphorylation of VP11/12 in Vero cells, strongly suggesting that VP11/12 participates in an Lck-mediated signaling pathway as a substrate of Lck or a kinase activated by Lck. We sought to elucidate signaling events downstream of VP11/12-SFK interactions. SFKs lie upstream of the canonical phosphoinositide 3-kinase (PI3K)-Akt pathway in signaling emanating from immune receptors, growth factor receptors, and polyomavirus middle T antigen. Here, we show that VP11/12 is required for virus-induced activation of PI3K-Akt signaling in HSV-infected Jurkat T cells and primary fibroblasts. VP11/12 interacts with PI3K or PI3K signaling complexes during infection, suggesting that VP11/12 activates PI3K directly. SFK activity is required for tyrosine phosphorylation of VP11/12, VP11/12-PI3K interactions, and Akt activation in infected fibroblasts, suggesting that SFK-dependent phosphorylation of VP11/12 is required for interactions with downstream signaling effectors. Akt controls many biological functions, including cell survival, cell motility, and translation, but it is currently unclear which Akt targets are modulated by VP11/12 during infection. Although the Akt target mTORC1 is activated during HSV-1 infection, VP11/12 is not required for this effect, implying that one or more additional viral proteins regulate this pathway. Further studies are therefore required to determine which Akt targets and associated biological functions are uniquely modulated by VP11/12.
| S-EPMC3067919 | biostudies-literature
Project description:Phosphoinositide-dependent kinase l (PDK1) phosphorylates and activates multiple AGC serine kinases, including protein kinase B (PKB), p70Ribosomal S6 kinase (S6K) and p90Ribosomal S6 kinase (RSK). PDK1 is required for thymocyte differentiation and proliferation, and herein, we explore the molecular basis for these essential functions of PDK1 in T lymphocyte development. A key finding is that PDK1 is required for the expression of key nutrient receptors in T cell progenitors: CD71 the transferrin receptor and CD98 a subunit of L-amino acid transporters. PDK1 is also essential for Notch-mediated trophic and proliferative responses in thymocytes. A PDK1 mutant PDK1 L155E, which supports activation of PKB but no other AGC kinases, can restore CD71 and CD98 expression in pre-T cells and restore thymocyte differentiation. However, PDK1 L155E is insufficient for thymocyte proliferation. The role of PDK1 in thymus development thus extends beyond its ability to regulate PKB. In addition, PDK1 phosphorylation of AGC kinases such as S6K and RSK is also necessary for thymocyte development.
| S-EPMC1933393 | biostudies-literature
Project description:Lysosomes and the yeast vacuole are degradative and acidic organelles. Phosphatidylinositol 3,5-bisphosphate (PtdIns(3,5)P2), a master architect of endolysosome and vacuole identity, is thought to be necessary for vacuolar acidification in yeast. There is also evidence that PtdIns(3,5)P2 may play a role in lysosomal acidification in higher eukaryotes. Nevertheless, these conclusions rely on qualitative assays of lysosome/vacuole pH. For example, quinacrine, an acidotropic fluorescent base, does not accumulate in the vacuoles of fab1Δ yeast. Fab1, along with its mammalian ortholog PIKfyve, is the lipid kinase responsible for synthesizing PtdIns(3,5)P2. In this study, we employed several assays that quantitatively assessed the lysosomal and vacuolar pH in PtdIns(3,5)P2-depleted cells. Using ratiometric imaging, we conclude that lysosomes retain a pH < 5 in PIKfyve-inhibited mammalian cells. In addition, quantitative fluorescence microscopy of vacuole-targeted pHluorin, a pH-sensitive GFP variant, indicates that fab1Δ vacuoles are as acidic as wild-type yeast. Importantly, we also employed fluorimetry of vacuoles loaded with cDCFDA, a pH-sensitive dye, to show that both wild-type and fab1Δ vacuoles have a pH < 5.0. In comparison, the vacuolar pH of the V-ATPase mutant vph1Δ or vph1Δ fab1Δ double mutant was 6.1. Although the steady-state vacuolar pH is not affected by PtdIns(3,5)P2 depletion, it may have a role in stabilizing the vacuolar pH during salt shock. Overall, we propose a model in which PtdIns(3,5)P2 does not govern the steady-state pH of vacuoles or lysosomes.
| S-EPMC4392288 | biostudies-literature
Project description:The tumour suppressor p53 (encoded by TP53) protects the genome against cellular stress and is frequently mutated in cancer. Mutant p53 acquires gain-of-function oncogenic activities that are dependent on its enhanced stability. However, the mechanisms by which nuclear p53 is stabilized are poorly understood. Here, we demonstrate that the stability of stress-induced wild-type and mutant p53 is regulated by the type I phosphatidylinositol phosphate kinase (PIPKI-α (also known as PIP5K1A)) and its product phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2). Nuclear PIPKI-α binds to p53 upon stress, resulting in the production and association of PtdIns(4,5)P2 with p53. PtdIns(4,5)P2 binding promotes the interaction between p53 and the small heat shock proteins HSP27 (also known as HSPB1) and αB-crystallin (also known as HSPB5), which stabilize nuclear p53. Moreover, inhibition of PIPKI-α or PtdIns(4,5)P2 association results in p53 destabilization. Our results point to a previously unrecognized role of nuclear phosphoinositide signalling in regulating p53 stability and implicate this pathway as a promising therapeutic target in cancer.
| S-EPMC7017954 | biostudies-literature
Project description:FIG4 is a phosphoinositide phosphatase that is mutated in several diseases including Charcot-Marie-Tooth Disease 4J (CMT4J) and Yunis-Varon syndrome (YVS). To investigate the mechanism of disease pathogenesis, we generated Drosophila models of FIG4-related diseases. Fig4 null mutant animals are viable but exhibit marked enlargement of the lysosomal compartment in muscle cells and neurons, accompanied by an age-related decline in flight ability. Transgenic animals expressing Drosophila Fig4 missense mutations corresponding to human pathogenic mutations can partially rescue lysosomal expansion phenotypes, consistent with these mutations causing decreased FIG4 function. Interestingly, Fig4 mutations predicted to inactivate FIG4 phosphatase activity rescue lysosome expansion phenotypes, and mutations in the phosphoinositide (3) phosphate kinase Fab1 that performs the reverse enzymatic reaction also causes a lysosome expansion phenotype. Since FIG4 and FAB1 are present together in the same biochemical complex, these data are consistent with a model in which FIG4 serves a phosphatase-independent biosynthetic function that is essential for lysosomal membrane homeostasis. Lysosomal phenotypes are suppressed by genetic inhibition of Rab7 or the HOPS complex, demonstrating that FIG4 functions after endosome-to-lysosome fusion. Furthermore, disruption of the retromer complex, implicated in recycling from the lysosome to Golgi, does not lead to similar phenotypes as Fig4, suggesting that the lysosomal defects are not due to compromised retromer-mediated recycling of endolysosomal membranes. These data show that FIG4 plays a critical noncatalytic function in maintaining lysosomal membrane homeostasis, and that this function is disrupted by mutations that cause CMT4J and YVS.
| S-EPMC4743688 | biostudies-literature
Project description:The insulin/IGF-IRS-PI3K-Akt pathway is highly conserved in evolution. To test whether this signaling cascade determines organ size in vertebrates, we have recently created mouse lines transgenic for constitutively active (caPI3K) and dominant-negative forms of PI3K (dnPI3K) (Shioi et al., 2000). Transgene expression is driven by the cardiac-specific a -myosin heavy chain (MHC) promoter. Both transgenic lines are characterized by moderate but highly consistent changes in heart size, despite the fact that body weight and the size of other organs are completely normal. caPI3K transgenic animals have hearts 20% larger than those of wild type littermates, whereas dnPI3K mice have hearts that are 17% smaller. The observed changes in heart size correlate with an appropriate increase or decrease in the size of transgenic cardiomyocytes. These hearts do not have cardiomyopathic changes, since the contractile function of transgenic hearts is normal, and signs of necrosis, apoptosis, or interstitial fibrosis are absent (see Physiology). These data suggest an autonomous role for PI3K in cell size regulation. Our goal is now to determine how activation of this system translates into changes in cell size by identifying the trigger and components of this signaling cascade. Heterozygous caPI3K (constitutively active PI3K) and dnPI3K (dominant-negative PI3K) transgenic female mice (5-14 months) compared with non-transgenic littermates. Transgene expression driven by the a -myosin heavy chain (a -MHC) promoter. Keywords: other
2003-07-24 | GSE558 | GEO