Localization of two distinct type III phosphatidylinositol 4-kinase enzyme mRNAs in the rat

PI4KIIIβ-Mediated Phosphoinositides Metabolism Regulates Function of the VTA Dopaminergic Neurons and Depression-Like Behavior

Phosphoinositides, including phosphatidylinositol-4,5-bisphosphate (PIP2), play a crucial role in controlling key cellular functions such as membrane and vesicle trafficking, ion channel, and transporter activity. Phosphatidylinositol 4-kinases (PI4K) are essential enzymes in regulating the turnover of phosphoinositides. However, the functional role of PI4Ks and mediated phosphoinositide metabolism in the central nervous system has not been fully revealed. In this study, we demonstrated that PI4KIIIβ, one of the four members of PI4Ks, is an important regulator of VTA dopaminergic neuronal activity and related depression-like behavior of mice by controlling phosphoinositide turnover. Our findings provide new insights into possible mechanisms and potential drug targets for neuropsychiatric diseases, including depression. Both sexes were studied in basic behavior tests, but only male mice could be used in the social defeat depression model.

In the line-up: deleted genes associated with DiGeorge/22q11.2 deletion syndrome: are they all suspects?

BACKGROUND

22q11.2 deletion syndrome (22q11DS), a copy number variation (CNV) disorder, occurs in approximately 1:4000 live births due to a heterozygous microdeletion at position 11.2 (proximal) on the q arm of human chromosome 22 (hChr22) (McDonald-McGinn and Sullivan, Medicine 90:1-18, 2011). This disorder was known as DiGeorge syndrome, Velo-cardio-facial syndrome (VCFS) or conotruncal anomaly face syndrome (CTAF) based upon diagnostic cardiovascular, pharyngeal, and craniofacial anomalies (McDonald-McGinn and Sullivan, Medicine 90:1-18, 2011; Burn et al., J Med Genet 30:822-4, 1993) before this phenotypic spectrum was associated with 22q11.2 CNVs. Subsequently, 22q11.2 deletion emerged as a major genomic lesion associated with vulnerability for several clinically defined behavioral deficits common to a number of neurodevelopmental disorders (Fernandez et al., Principles of Developmental Genetics, 2015; Robin and Shprintzen, J Pediatr 147:90-6, 2005; Schneider et al., Am J Psychiatry 171:627-39, 2014).

RESULTS

The mechanistic relationships between heterozygously deleted 22q11.2 genes and 22q11DS phenotypes are still unknown. We assembled a comprehensive "line-up" of the 36 protein coding loci in the 1.5 Mb minimal critical deleted region on hChr22q11.2, plus 20 protein coding loci in the distal 1.5 Mb that defines the 3 Mb typical 22q11DS deletion. We categorized candidates based upon apparent primary cell biological functions. We analyzed 41 of these genes that encode known proteins to determine whether haploinsufficiency of any single 22q11.2 gene-a one gene to one phenotype correspondence due to heterozygous deletion restricted to that locus-versus complex multigenic interactions can account for single or multiple 22q11DS phenotypes.

CONCLUSIONS

Our 22q11.2 functional genomic assessment does not support current theories of single gene haploinsufficiency for one or all 22q11DS phenotypes. Shared molecular functions, convergence on fundamental cell biological processes, and related consequences of individual 22q11.2 genes point to a matrix of multigenic interactions due to diminished 22q11.2 gene dosage. These interactions target fundamental cellular mechanisms essential for development, maturation, or homeostasis at subsets of 22q11DS phenotypic sites.

Recent advances in understanding phosphoinositide signaling in the nervous system

Polyphosphoinositides (PPIn) are essential signaling phospholipids that make remarkable contributions to the identity of all cellular membranes and signaling cascades in mammalian cells. They exert regulatory control over membrane homeostasis via selective interactions with cellular proteins at the membrane–cytoplasm interface. This review article briefly summarizes our current understanding of the key roles that PPIn play in orchestrating and regulating crucial electrical and chemical signaling events in mammalian neurons and the significant neuro-pathophysiological conditions that arise following alterations in their metabolism.

Germline recessive mutations in PI4KA are associated with perisylvian polymicrogyria, cerebellar hypoplasia and arthrogryposis

Polymicrogyria (PMG) is a structural brain abnormality involving the cerebral cortex that results from impaired neuronal migration and although several genes have been implicated, many cases remain unsolved. In this study, exome sequencing in a family where three fetuses had all been diagnosed with PMG and cerebellar hypoplasia allowed us to identify regions of the genome for which both chromosomes were shared identical-by-descent, reducing the search space for causative variants to 8.6% of the genome. In these regions, the only plausibly pathogenic mutations were compound heterozygous variants in PI4KA, which Sanger sequencing confirmed segregated consistent with autosomal recessive inheritance. The paternally transmitted variant predicted a premature stop mutation (c.2386C>T; p.R796X), whereas the maternally transmitted variant predicted a missense substitution (c.5560G>A; p.D1854N) at a conserved residue within the catalytic domain. Functional studies using expressed wild-type or mutant PI4KA enzyme confirmed the importance of p.D1854 for kinase activity. Our results emphasize the importance of phosphoinositide signalling in early brain development.

Phosphoinositides: tiny lipids with giant impact on cell regulation

Phosphoinositides (PIs) make up only a small fraction of cellular phospholipids, yet they control almost all aspects of a cell's life and death. These lipids gained tremendous research interest as plasma membrane signaling molecules when discovered in the 1970s and 1980s. Research in the last 15 years has added a wide range of biological processes regulated by PIs, turning these lipids into one of the most universal signaling entities in eukaryotic cells. PIs control organelle biology by regulating vesicular trafficking, but they also modulate lipid distribution and metabolism via their close relationship with lipid transfer proteins. PIs regulate ion channels, pumps, and transporters and control both endocytic and exocytic processes. The nuclear phosphoinositides have grown from being an epiphenomenon to a research area of its own. As expected from such pleiotropic regulators, derangements of phosphoinositide metabolism are responsible for a number of human diseases ranging from rare genetic disorders to the most common ones such as cancer, obesity, and diabetes. Moreover, it is increasingly evident that a number of infectious agents hijack the PI regulatory systems of host cells for their intracellular movements, replication, and assembly. As a result, PI converting enzymes began to be noticed by pharmaceutical companies as potential therapeutic targets. This review is an attempt to give an overview of this enormous research field focusing on major developments in diverse areas of basic science linked to cellular physiology and disease.

The phosphatidylinositol 4-kinases: don't call it a comeback

Phosphatidylinositol 4-phosphate (PtdIns4P) is a quantitatively minor membrane phospholipid which is the precursor of PtdIns(4,5)P (2) in the classical agonist-regulated phospholipase C signalling pathway. However, PtdIns4P also governs the recruitment and function of numerous trafficking molecules, principally in the Golgi complex. The majority of phosphoinositides (PIs) phosphorylated at the D4 position of the inositol headgroup are derived from PtdIns4P and play roles in a diverse array of fundamental cellular processes including secretion, cell migration, apoptosis and mitogenesis; therefore, PtdIns4P biosynthesis can be regarded as key point of regulation in many PI-dependent processes.Two structurally distinct sequence families, the type II and type III PtdIns 4-kinases, are responsible for PtdIns4P synthesis in eukaryotic organisms. These important proteins are differentially expressed, localised and regulated by distinct mechanisms, indicating that the enzymes perform non-redundant roles in trafficking and signalling. In recent years, major advances have been made in our understanding of PtdIns4K biology and here we summarise current knowledge of PtdIns4K structure, function and regulation.

Mammalian phosphoinositide kinases and phosphatases

Phosphoinositides are lipids that are present in the cytoplasmic leaflet of a cell's plasma and internal membranes and play pivotal roles in the regulation of a wide variety of cellular processes. Phosphoinositides are molecularly diverse due to variable phosphorylation of the hydroxyl groups of their inositol rings. The rapid and reversible configuration of the seven known phosphoinositide species is controlled by a battery of phosphoinositide kinases and phosphoinositide phosphatases, which are thus critical for phosphoinositide isomer-specific localization and functions. Significantly, a given phosphoinositide generated by different isozymes of these phosphoinositide kinases and phosphatases can have different biological effects. In mammals, close to 50 genes encode the phosphoinositide kinases and phosphoinositide phosphatases that regulate phosphoinositide metabolism and thus allow cells to respond rapidly and effectively to ever-changing environmental cues. Understanding the distinct and overlapping functions of these phosphoinositide-metabolizing enzymes is important for our knowledge of both normal human physiology and the growing list of human diseases whose etiologies involve these proteins. This review summarizes the structural and biological properties of all the known mammalian phosphoinositide kinases and phosphoinositide phosphatases, as well as their associations with human disorders.

Pulmonary fibrosis: pathogenesis, etiology and regulation

Pulmonary fibrosis and architectural remodeling of tissues can severely disrupt lung function, often with fatal consequences. The etiology of pulmonary fibrotic diseases is varied, with an array of triggers including allergens, chemicals, radiation and environmental particles. However, the cause of one of the most common pulmonary fibrotic conditions, idiopathic pulmonary fibrosis (IPF), is still unclear. This review examines common mechanisms of pulmonary wound-healing responses following lung injury, and highlights the pathogenesis of some of the most widespread pulmonary fibrotic diseases. A three phase model of wound repair is reviewed that includes; (1) injury; (2) inflammation; and (3) repair. In most pulmonary fibrotic conditions dysregulation at one or more of these phases has been reported. Chronic inflammation can lead to an imbalance in the production of chemokines, cytokines, growth factors, and disrupt cellular recruitment. These changes coupled with excessive pro-fibrotic IL-13 and/or TGFbeta1 production can turn a well-controlled healing response into a pathogenic fibrotic response. Endogenous regulatory mechanisms are discussed including novel areas of therapeutic intervention. Restoring homeostasis to these dysregulated healing responses, or simply neutralizing the key pro-fibrotic mediators may prevent or slow the progression of pulmonary fibrosis.

Targeting phosphoinositide 3-kinase: moving towards therapy

Phosphoinositide 3-kinases (PI3K) orchestrate cell responses including mitogenic signaling, cell survival and growth, metabolic control, vesicular trafficking, degranulation, cytoskeletal rearrangement and migration. Deregulation of the PI3K pathway occurs by activating mutations in growth factor receptors or the PIK3CA locus coding for PI3Kalpha, by loss of function of the lipid phosphatase and tensin homolog deleted in chromosome ten (PTEN/MMAC/TEP1), by the up-regulation of protein kinase B (PKB/Akt), or the impairment of the tuberous sclerosis complex (TSC1/2). All these events are linked to growth and proliferation, and have thus prompted a significant interest in the pharmaceutical targeting of the PI3K pathway in cancer. Genetic targeting of PI3Kgamma (p110gamma) and PI3Kdelta (p110delta) in mice has underlined a central role of these PI3K isoforms in inflammation and allergy, as they modulate chemotaxis of leukocytes and degranulation in mast cells. Proof-of-concept molecules selective for PI3Kgamma have already successfully alleviated disease progress in murine models of rheumatoid arthritis and lupus erythematosus. As targeting PI3K moves forward to therapy of chronic, non-fatal disease, safety concerns for PI3K inhibitors increase. Many of the present inhibitor series interfere with target of rapamycin (TOR), DNA-dependent protein kinase (DNA-PK(cs)) and activity of the ataxia telangiectasia mutated gene product (ATM). Here we review the current disease-relevant knowledge for isoform-specific PI3K function in the above mentioned diseases, and review the progress of >400 recent patents covering pharmaceutical targeting of PI3K. Currently, several drugs targeting the PI3K pathway have entered clinical trials (phase I) for solid tumors and suppression of tissue damage after myocardial infarction (phases I,II).

Inositol 1,4,5 trisphosphate receptor and chromogranin B are concentrated in different regions of the hippocampus

Calcium (Ca(2+)) release from intracellular stores plays a crucial role in many cellular functions in the brain. These intracellular signals have been shown to be transmitted within and between cells. We report a non-uniform distribution of proteins essential for Ca(2+) signaling in acutely prepared brain slice preparations and organotypic slice cultures, both made from rat hippocampus. The Type I inositol-1,4,5 trisphosphate receptor (InsP(3)R1) is the main InsP(3)R subtype in neurons. Immunohistochemistry experiments showed a prominent expression of InsP(3)R1 in the CA1 region of the hippocampus whereas the CA3 region and dentate gyrus (DG) showed only moderate immunoreactivity. In contrast, chromogranin B (CGB), a protein binding to the InsP(3)R1 on the luminal side of the endoplasmic reticular membrane was enriched in the CA3 region whereas DG and the CA1 region showed only faint CGB signals. The neuronal kinases leading to the formation of inositol-1,4,5 trisphosphate (InsP(3)), phosphatidylinositol-4-kinase (PI4K), and phosphatidylinositol-4-phosphate-5-kinase (PIPK), showed strong immunoreactivity throughout all hippocampal cell fields with differences in the subcellular distribution. Moreover, a distinct band of strong CGB and PIPK immunoreactivity was observed in the CA3 region that coincides with the mossy fiber tract (stratum lucidum). These data show differential expression of the components of the signaling toolkit leading to InsP(3)-mediated Ca(2+) release in cells of the hippocampus. The regulation of these differences may play an important role in various neuropathologic conditions such as Alzheimer's disease, epilepsy, or schizophrenia.

Chemical modification of interleukin-10 with mannose 6-phosphate groups yields a liver-selective cytokine

Cytokines are considered a promising immunotherapy for chronic diseases, because of their potency and fundamental roles in pathological processes. However, their therapeutic use is limited because of their poor pharmacokinetics and pleiotropic effects in various organs. These problems may be overcome by cell-specific delivery of the cytokine. This approach involves chemical modification of the protein with homing devices that recognize receptors on target cells. The cytokine interleukin-10 (IL10) may be valuable as a therapeutic cytokine for patients with liver cirrhosis. However, its rapid renal elimination and general immunosuppressive activities limit therapeutic use. We therefore aim to target this cytokine in the liver, in particular to fibrogenic hepatic stellate cells (HSCs). We show that IL10 is successfully modified with mannose 6-phosphate (M6P), which is a homing device for the mannose 6-phosphate/insulin-like growth factor II (M6P/IGFII) receptor expressed on activated HSCs. Chemical modification did not diminish IL10 efficacy with regard to in vitro anti-inflammatory (lipopolysaccharide-stimulated tumor necrosis factor alpha release) and antifibrotic (collagen deposition and degradation) activities. Biodistribution studies with radiolabeled M6P-IL10 and IL10 in rats with liver fibrosis showed that modification with M6P groups induced a shift in the distribution from the kidneys (IL10) to the liver (M6P-IL10). Hepatocellular binding of M6P-IL10 occurred via M6P/IGFII receptors and scavenger receptors, indicating that not only HSCs but also Kupffer and endothelial cells are target cells. IL10 did not bind to these receptors. We conclude that we prepared an active and liver-specific form of the cytokine IL10 that can be evaluated for its efficacy to treat liver diseases.

Nucleolar localization of phosphatidylinositol 4-kinase PI4K230 in various mammalian cells

BACKGROUND

Previous immunohistochemical investigations could not detect PI4K230, an isoform of mammalian phosphatidylinositol 4-kinases (also called type III alpha), in the nucleus and nucleolus of cells in spite of its predicted nuclear localization signals.

METHODS

Immunofluorescent detection of PI4K230 and other PI4K isoforms was performed on formaldehyde (PFA) or ethanol fixed cells and rat brain cryosections. Costaining with nucleolin and the effect of siRNA, Triton X-100, DNase, and RNase treatments were also tested to determine the localization of PI4K230.

RESULTS

PI4K230 gives a prominent signal in the nucleolus of ethanol fixed rat brain cryosections and of several cell types in addition to its presence in the nucleus and cytoplasm. The PI4K230 immunoreactivity of the nucleolus is masked in PFA fixed cells, but it can be restored by treatment of PFA fixed cells with hot wet citrate buffer or by washing the cryosections with PBS prior to PFA fixation. Nucleolar PI4K230 occurs in a Triton X-100 resistant complex. Treatment of COS-7 cells with siRNA targeting PI4K230 and permeabilized B50 cells with DNase or RNase results in the loss of PI4K230 signal from the nucleolus.

CONCLUSION

These experiments suggest the participation of PI4K230 in a DNase and RNase sensitive complex with a unique localization and function in the nucleolus.

Effects of iron deficiency on the secretion of interleukin-10 by mitogen-activated and non-activated murine spleen cells

Interleukin (IL)-10 plays crucial regulatory roles in immune responses by inhibiting the secretion of several cytokines (IL-2, IL-12, interferon-gamma (IFN-gamma)) and lymphocyte proliferation. Iron deficiency, a public health problem for children, alters these immune responses. To determine whether these changes are related to altered IL-10 secretion, we measured IL-10 in 24 and 48 h supernatant of spleen cell cultures from iron deficient (ID), control (C), pairfed (PF), and ID mice fed the control diet (iron repletion) for 3 (R3) and 14 (R14) days (d, n = 12/group). Mean levels of hemoglobin, hematocrit, and liver iron stores varied as follows: C approximately equal PF approximately equal R14 > R3 > ID (P < 0.01). Mean baseline IL-10 levels of ID mice tended to be higher than those of other groups (P > 0.05, ANOVA). Mean IL-10 levels secreted by concanavalin A (Con A) and antibody raised against cluster of differentiation molecule 3 (anti-CD3)-treated cells (+/-background) were lower in ID than in C (48 h) and iron replete mice (P < 0.05). Underfeeding also reduced IL-10 secretion by anti-CD3-treated cells (48 h, P < 0.05). Lymphocyte proliferative responses to anti-CD3 +/- anti-CD28 antibodies were lower in ID than in C and PF mice, and they were corrected by iron repletion (P < 0.05). IL-10 levels negatively correlated with indicators of iron status (r <or= -0.285) and lymphocyte proliferation (r <or= -0.379 [r <or= -0.743 for ID mice]), but positively correlated with IFN-gamma levels (r <or= 0.47; P < 0.05). Data suggest that iron deficiency has a generalized deleterious effect on cells that secrete both cytokines. Reduced IL-10 secretion by activated cells does not overcome the inhibition of lymphocyte proliferation due to other factors of T cell activation that are regulated by iron.

Transgenic overexpression of interleukin (IL)-10 in the lung causes mucus metaplasia, tissue inflammation, and airway remodeling via IL-13-dependent and -independent pathways

To address the complex chronic effector properties of interleukin (IL)-10, we generated transgenic mice in which IL-10 was overexpressed in the lung. In these mice, IL-10 inhibited endotoxin-induced tumor necrosis factor production and neutrophil accumulation. IL-10 also caused mucus metaplasia, B and T cell-rich inflammation, and subepithelial fibrosis and augmented the levels of mRNA encoding Gob-5, mucins, and IL-13. In mice bred to have null mutations of IL-13, IL-4R(alpha), or STAT-6, transgenic IL-10 did not induce mucus metaplasia but did induce inflammation and fibrosis. IL-10 was also a critical mucin regulator of virus-induced mucus metaplasia. Thus, IL-10, although inhibiting lipopolysaccharide-induced inflammation, also causes mucus metaplasia, tissue inflammation, and airway fibrosis. These responses are mediated by multiple mechanisms with mucus metaplasia being dependent on and the inflammation and fibrosis being independent of an IL-13/IL-4R(alpha)/STAT-6 activation pathway.

Pro- and anti-inflammatory cytokines regulate insulin-like growth factor binding protein production by fetal rat lung fibroblasts

The inflammatory response of the lung to noxious factors contributes to the pathogenesis of chronic lung injury. Inflammatory mediators regulate the insulin-like growth factor (IGF) system, a key modulator of lung fibroblast proliferation. The activity of IGFs is regulated by IGF-binding proteins (IGFBPs) secreted by lung cells. To investigate the regulation of lung fibroblast IGFBPs by cytokines, we exposed 19-d fetal rat lung fibroblasts to various pro- and anti-inflammatory mediators. IGFBP abundance in conditioned medium (CM) was measured by ligand blot and RNA transcript abundance by RNase protection assays. Fetal rat lung fibroblasts exposed to interleukin (IL)-1beta or tumor necrosis factor (TNF)-alpha for 48 h demonstrated increased abundance of CM IGFBP-3 (5.9- and 4.7-fold increases for IL-1beta and TNF-alpha, respectively) and IGFBP-4 (5.7- and 7.4-fold increases for IL-1beta and TNF-alpha, respectively) that was accompanied by a small increase in IGFBP-4 mRNA and a larger increase in IGFBP-3 mRNA abundance. IGFBP-4 specific proteolysis was examined in CM collected from fetal rat lung fibroblasts after incubation with serum-free medium (SFM), IL-1beta, or TNF-alpha for 48 h. Cell-free aliquots of SFM-CM incubated at 37C for 24 h showed a 65% decrease in IGFBP-4 abundance that was inhibited by 1,10-phenanthroline. In contrast, CM from cells exposed to IL-1beta or TNF-alpha incubated at 37 degrees C for 24 h did not show a significant decrease in IGFBP-4 abundance unless IGF-I was present during the cell-free incubation. Addition of IGFBP-3 to aliquots of SFM-CM reversed the IGF-I-mediated acceleration of IGFBP-4 proteolysis. Similarly, addition of IGFBP-3 to cells in culture increased the accumulation of CM IGFBP-4. These results demonstrate that cytokines regulate IGFBP production and clearance by fetal lung cells and suggest a mechanism by which cytokines regulate cell proliferation following lung injury.

Synthesis of new cyclitol compounds that influence the activity of phosphatidylinositol 4-kinase isoform, PI4K230

The synthesis, chemical derivatization, and investigation of the inhibitory properties of novel cyclitol derivatives on the phosphatidylinositol 4-kinase enzymes PI4K55 and PI4K230 involved in the phosphatidylinositol cycle are reported. Some of the prepared cyclitol derivatives (i.e. 9, 11, 12, and 14) proved to be very powerful and specific irreversible inhibitors of PI4K230 at or below a concentration of 1 mM.