Probing phosphoinositide functions in signaling and membrane trafficking

Division of Cell Signalling, School of Life Sciences, MSI/WTB Complex, University of Dundee, Dundee DD1 5EH, Scotland, UK.
Trends in Cell Biology (Impact Factor: 12.01). 06/2005; 15(5):259-68. DOI: 10.1016/j.tcb.2005.03.008
Source: PubMed


The inositol phospholipids (PIs) comprise a family of eight species with different combinations of phosphate groups arranged around the inositol ring. PIs are among the most versatile signaling molecules known, with key roles in receptor-mediated signal transduction, actin remodeling and membrane trafficking. Recent studies have identified effector proteins and specific lipid-binding domains through which PIs signal. These lipid-binding domains can be used as probes to further our understanding of the spatial and temporal control of individual PI species. New layers of complexity revealed by the use of such probes include the occurrence of PIs at intracellular locations, the identification of phosphatidylinositol signaling hotspots and the presence of non-membrane pools of PIs in cell nuclei.

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Available from: John Lucocq, Oct 04, 2015
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    • "The generation of phosphatidylinositol (3,4,5) triphosphate [PtdIns(3,4,5)P3] by type I phosphoinositide (PI) 3-kinases is affected by a number of growth factors and cytokines, many of which are influenced by HSPGs as accessory molecules. PtdIns(3,4,5)P3 affects a number of trafficking events, including endocytosis and autophagy (Downes et al. 2005). "
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    ABSTRACT: The identification and validation of gene-gene interactions is a major challenge in human studies. Here, we explore an approach for studying epistasis in humans using a Drosophila melanogaster model of neonatal diabetes mellitus. Expression of the mutant preproinsulin (hINS(C96Y)) in the eye imaginal disc mimics the human disease: it activates conserved stress response pathways and leads to cell death (reduction in eye area). Dominant-acting variants in wild-derived inbred lines from the Drosophila Genetics Reference Panel produce a continuous, highly heritable distribution of eye degeneration phenotypes in a hINS(C96Y) background. A genome-wide association study (GWAS) in 154 sequenced lines identified a sharp peak on chromosome 3L, which mapped to a 400bp linkage block within an intron of the gene sulfateless (sfl). RNAi knock-down of sfl enhanced the eye degeneration phenotype in a mutant-hINS-dependent manner. RNAi against two additional genes in the heparan sulfate (HS) biosynthetic pathway (ttv and botv), in which sfl acts, also modified the eye phenotype in a hINS(C96Y)-dependent manner, strongly suggesting a novel link between HS-modified proteins and cellular responses to misfolded proteins. Finally, we evaluated allele-specific expression difference between the two major sfl-intronic haplotypes in heterozygtes. The results showed significant heterogeneity in marker-associated gene expression, thereby leaving the causal mutation(s) and its mechanism unidentified. In conclusion, the ability to create a model of human genetic disease, map a QTL by GWAS to a specific gene, validate its contribution to disease with available genetic resources, and the potential to experimentally link the variant to a molecular mechanism, demonstrate the many advantages Drosophila holds in determining the genetic underpinnings of human disease.
    Genetics 02/2014; 196(2):557-567. DOI:10.1534/genetics.113.157800 · 5.96 Impact Factor
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    • "In addition to this, myo-inositol also contributes to plant protection against salinity by restoring the turgor pressure and protecting cellular structures from reactive oxygen species stress (Loewus and Murthy 2000; Majumder and Biswas 2006). Therefore, any changes in the levels of myo-inositol due to perturbation of MIPS may lead to alteration of the compounds synthesized later in the pathway, which can further disturb the signaling mechanism that regulates plants responses to different environmental stresses (Stevenson et al. 2000; Downes et al. 2005). Another important aspect of phytate reduction is associated with an increase in the amount of iron in seeds. "
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    ABSTRACT: Background Phytic acid (InsP6) is considered as the major source of phosphorus and inositol phosphates in cereal grains. Reduction of phytic acid level in cereal grains is desirable in view of its antinutrient properties to maximize mineral bioavailability and minimize the load of phosphorus waste management. We report here RNAi mediated seed-specific silencing of myo-inositol-3-phosphate synthase (MIPS) gene catalyzing the first step of phytic acid biosynthesis in rice. Moreover, we also studied the possible implications of MIPS silencing on myo-inositol and related metabolism, since, first step of phytic acid biosynthesis is also the rate limiting step of myo-inositol synthesis, catalyzed by MIPS. Results The resulting transgenic rice plants (T3) showed a 4.59 fold down regulation in MIPS gene expression, which corresponds to a significant decrease in phytate levels and a simultaneous increment in the amount of inorganic phosphate in the seeds. A diminution in the myo-inositol content of transgenic plants was also observed due to disruption of the first step of phytic acid biosynthetic pathway, which further reduced the level of ascorbate and altered abscisic acid (ABA) sensitivity of the transgenic plants. In addition, our results shows that in the transgenic plants, the lower phytate levels has led to an increment of divalent cations, of which a 1.6 fold increase in the iron concentration in milled rice seeds was noteworthy. This increase could be attributed to reduced chelation of divalent metal (iron) cations, which may correlate to higher iron bioavailability in the endosperm of rice grains. Conclusion The present study evidently suggests that seed-specific silencing of MIPS in transgenic rice plants can yield substantial reduction in levels of phytic acid along with an increase in inorganic phosphate content. However, it was also demonstrated that the low phytate seeds had an undesirable diminution in levels of myo-inositol and ascorbate, which probably led to sensitiveness of seeds to abscisic acid during germination. Therefore, it is suggested that though MIPS is the prime target for generation of low phytate transgenic plants, down-regulation of MIPS can have detrimental effect on myo-inositol synthesis and related pathways which are involved in key plant metabolism.
    Rice 11/2013; 6(1). DOI:10.1186/1939-8433-6-12 · 3.92 Impact Factor
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    • "Besides a requirement in plant growth and development, myo-inositol is also used as a precursor and substrate for many crucial metabolites in plants such as phytate, phosphatidylinositol, galactinol, ascorbate, indole acetic acid conjugate, ononitol, and pinitol. These inositol derivatives were shown to be implicated in various physiological processes including plant stress adaptation (Gross and Boss, 1993; Loewus and Murthy, 2000; Downes et al., 2005; Nunes et al., 2006; Meng et al., 2009; Chaouch and Noctor, 2010; Donahue et al., 2010). The de novo synthesis of myo-inositol is a two-step process and is 5624 | Saxena et al. highly conserved among biological organisms. "
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    ABSTRACT: myo-Inositol monophosphatase (IMP) is an essential enzyme in the myo-inositol metabolic pathway where it primarily dephosphorylates myo-inositol 1-phosphate to maintain the cellular inositol pool which is important for many metabolic and signalling pathways in plants. The stress-induced increased accumulation of inositol has been reported in a few plants including chickpea; however, the role and regulation of IMP is not well defined in response to stress. In this work, it has been shown that IMP activity is distributed in all organs in chickpea and was noticeably enhanced during environmental stresses. Subsequently, using degenerate oligonucleotides and RACE strategy, a full-length IMP cDNA (CaIMP) was cloned and sequenced. Biochemical study revealed that CaIMP encodes a lithium-sensitive phosphatase enzyme with broad substrate specificity, although maximum activity was observed with the myo-inositol 1-phosphate and l-galactose 1-phosphate substrates. Transcript analysis revealed that CaIMP is differentially expressed and regulated in different organs, stresses and phytohormones. Complementation analysis in Arabidopsis further confirmed the role of CaIMP in l-galactose 1-phosphate and myo-inositol 1-phosphate hydrolysis and its participation in myo-inositol and ascorbate biosynthesis. Moreover, Arabidopsis transgenic plants over-expressing CaIMP exhibited improved tolerance to stress during seed germination and seedling growth, while the VTC4/IMP loss-of-function mutants exhibited sensitivity to stress. Collectively, CaIMP links various metabolic pathways and plays an important role in improving seed germination and seedling growth, particularly under stressful environments.
    Journal of Experimental Botany 10/2013; 64(18). DOI:10.1093/jxb/ert336 · 5.53 Impact Factor
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