Metabolic supervision by PPIP5K, an inositol pyrophosphate kinase/phosphatase, controls proliferation of the HCT116 tumor cell line.

Identification of common patterns of cancer metabolic reprogramming could assist the development of new therapeutic strategies. Recent attention in this field has focused on identifying and targeting signal transduction pathways that interface directly with major metabolic control processes. In the current study we demonstrate the importance of signaling by the diphosphoinositol pentakisphosphate kinases (PPIP5Ks) to the metabolism and proliferation of the HCT116 colonic tumor cell line. We observed reciprocal cross talk between PPIP5K catalytic activity and glucose metabolism, and we show that CRISPR-mediated PPIP5K deletion suppresses HCT116 cell proliferation in glucose-limited culture conditions that mimic the tumor cell microenvironment. We conducted detailed, global metabolomic analyses of wild-type and PPIP5K knockout (KO) cells by measuring both steady-state metabolite levels and by performing isotope tracing experiments. We attribute the growth-impaired phenotype to a specific reduction in the supply of precursor material for de novo nucleotide biosynthesis from the one carbon serine/glycine pathway and the pentose phosphate pathway. We identify two enzymatic control points that are inhibited in the PPIP5K KO cells: serine hydroxymethyltransferase and phosphoribosyl pyrophosphate synthetase, a known downstream target of AMP-regulated protein kinase, which we show is noncanonically activated independently of adenine nucleotide status. Finally, we show the proliferative defect in PPIP5K KO cells can be significantly rescued either by addition of inosine monophosphate or a nucleoside mixture or by stable expression of PPIP5K activity. Overall, our data describe multiple, far-reaching metabolic consequences for metabolic supervision by PPIP5Ks in a tumor cell line.

Control of XPR1-dependent cellular phosphate efflux by InsP8 is an exemplar for functionally-exclusive inositol pyrophosphate signaling.

Homeostasis of cellular fluxes of inorganic phosphate (Pi) supervises its structural roles in bones and teeth, its pervasive regulation of cellular metabolism, and its functionalization of numerous organic compounds. Cellular Pi efflux is heavily reliant on Xenotropic and Polytropic Retrovirus Receptor 1 (XPR1), regulation of which is largely unknown. We demonstrate specificity of XPR1 regulation by a comparatively uncharacterized member of the inositol pyrophosphate (PP-InsP) signaling family: 1,5-bis-diphosphoinositol 2,3,4,6-tetrakisphosphate (InsP8). XPR1-mediated Pi efflux was inhibited by reducing cellular InsP8 synthesis, either genetically (knockout [KO] of diphosphoinositol pentakisphosphate kinases [PPIP5Ks] that synthesize InsP8) or pharmacologically [cell treatment with 2.5 µM dietary flavonoid or 10 µM N2-(m-trifluorobenzyl), N6-(p-nitrobenzyl) purine], to inhibit inositol hexakisphosphate kinases upstream of PPIP5Ks. Attenuated Pi efflux from PPIP5K KO cells was quantitatively phenocopied by KO of XPR1 itself. Moreover, Pi efflux from PPIP5K KO cells was rescued by restoration of InsP8 levels through transfection of wild-type PPIP5K1; transfection of kinase-dead PPIP5K1 was ineffective. Pi efflux was also rescued in a dose-dependent manner by liposomal delivery of a metabolically resistant methylene bisphosphonate (PCP) analog of InsP8; PCP analogs of other PP-InsP signaling molecules were ineffective. High-affinity binding of InsP8 to the XPR1 N-terminus (Kd = 180 nM) was demonstrated by isothermal titration calorimetry. To derive a cellular biology perspective, we studied biomineralization in the Soas-2 osteosarcoma cell line. KO of PPIP5Ks or XPR1 strongly reduced Pi efflux and accelerated differentiation to the mineralization end point. We propose that catalytically compromising PPIP5K mutations might extend an epistatic repertoire for XPR1 dysregulation, with pathological consequences for bone maintenance and ectopic calcification.

InsP7 is a small-molecule regulator of NUDT3-mediated mRNA decapping and processing-body dynamics.

Regulation of enzymatic 5' decapping of messenger RNA (mRNA), which normally commits transcripts to their destruction, has the capacity to dynamically reshape the transcriptome. For example, protection from 5' decapping promotes accumulation of mRNAs into processing (P) bodies-membraneless, biomolecular condensates. Such compartmentalization of mRNAs temporarily removes them from the translatable pool; these repressed transcripts are stabilized and stored until P-body dissolution permits transcript reentry into the cytosol. Here, we describe regulation of mRNA stability and P-body dynamics by the inositol pyrophosphate signaling molecule 5-InsP7 (5-diphosphoinositol pentakisphosphate). First, we demonstrate 5-InsP7 inhibits decapping by recombinant NUDT3 (Nudix [nucleoside diphosphate linked moiety X]-type hydrolase 3) in vitro. Next, in intact HEK293 and HCT116 cells, we monitored the stability of a cadre of NUDT3 mRNA substrates following CRISPR-Cas9 knockout of PPIP5Ks (diphosphoinositol pentakisphosphate 5-kinases type 1 and 2, i.e., PPIP5K KO), which elevates cellular 5-InsP7 levels by two- to threefold (i.e., within the physiological rheostatic range). The PPIP5K KO cells exhibited elevated levels of NUDT3 mRNA substrates and increased P-body abundance. Pharmacological and genetic attenuation of 5-InsP7 synthesis in the KO background reverted both NUDT3 mRNA substrate levels and P-body counts to those of wild-type cells. Furthermore, liposomal delivery of a metabolically resistant 5-InsP7 analog into wild-type cells elevated levels of NUDT3 mRNA substrates and raised P-body abundance. In the context that cellular 5-InsP7 levels normally fluctuate in response to changes in the bioenergetic environment, regulation of mRNA structure by this inositol pyrophosphate represents an epitranscriptomic control process. The associated impact on P-body dynamics has relevance to regulation of stem cell differentiation, stress responses, and, potentially, amelioration of neurodegenerative diseases and aging.

Correction: Bacillus anthracis Spore Surface Protein BclA Mediates Complement Factor H Binding to Spores and Promotes Spore Persistence.

[This corrects the article DOI: 10.1371/journal.ppat.1005678.].

Mutations in Diphosphoinositol-Pentakisphosphate Kinase PPIP5K2 are associated with hearing loss in human and mouse.

Autosomal recessive nonsyndromic hearing loss is a genetically heterogeneous disorder. Here, we report a severe-to-profound sensorineural hearing loss locus, DFNB100 on chromosome 5q13.2-q23.2. Exome enrichment followed by massive parallel sequencing revealed a c.2510G>A transition variant in PPIP5K2 that segregated with DFNB100-associated hearing loss in two large apparently unrelated Pakistani families. PPIP5Ks enzymes interconvert 5-IP7 and IP8, two key members of the inositol pyrophosphate (PP-IP) cell-signaling family. Their actions at the interface of cell signaling and bioenergetic homeostasis can impact many biological processes. The c.2510G>A transition variant is predicted to substitute a highly invariant arginine residue with histidine (p.Arg837His) in the phosphatase domain of PPIP5K2. Biochemical studies revealed that the p.Arg837His variant reduces the phosphatase activity of PPIP5K2 and elevates its kinase activity. We found that in mouse inner ear, PPIP5K2 is expressed in the cochlear and vestibular sensory hair cells, supporting cells and spiral ganglion neurons. Mice homozygous for a targeted deletion of the Ppip5k2 phosphatase domain exhibit degeneration of cochlear outer hair cells and elevated hearing thresholds. Our demonstration that PPIP5K2 has a role in hearing in humans indicates that PP-IP signaling is important to hair cell maintenance and function within inner ear.

KO of 5-InsP7 kinase activity transforms the HCT116 colon cancer cell line into a hypermetabolic, growth-inhibited phenotype.

The inositol pyrophosphates 5-InsP7 (diphosphoinositol pentakisphosphate) and 1,5-InsP8 (bis-diphosphoinositol tetrakisphosphate) are highly energetic cellular signals interconverted by the diphosphoinositol pentakisphosphate kinases (PPIP5Ks). Here, we used CRISPR to KO PPIP5Ks in the HCT116 colon cancer cell line. This procedure eliminates 1,5-InsP8 and raises 5-InsP7 levels threefold. Expression of p53 and p21 was up-regulated; proliferation and G1/S cell-cycle transition slowed. Thus, PPIP5Ks are potential targets for tumor therapy. Deletion of the PPIP5Ks elevated [ATP] by 35%; both [ATP] and [5-InsP7] were restored to WT levels by overexpression of PPIP5K1, and a kinase-compromised PPIP5K1 mutant had no effect. This covariance of [ATP] with [5-InsP7] provides direct support for an energy-sensing attribute (i.e., 1 mM Km for ATP) of the 5-InsP7-generating inositol hexakisphosphate kinases (IP6Ks). We consolidate this conclusion by showing that 5-InsP7 levels are elevated on direct delivery of ATP into HCT116 cells using liposomes. Elevated [ATP] in PPIP5K-/- HCT116 cells is underpinned by increased mitochondrial oxidative phosphorylation and enhanced glycolysis. To distinguish between 1,5-InsP8 and 5-InsP7 as drivers of the hypermetabolic and p53-elevated phenotypes, we used IP6K2 RNAi and the pan-IP6K inhibitor, N2-(m-trifluorobenzyl), N6-(p-nitrobenzyl) purine (TNP), to return 5-InsP7 levels in PPIP5K-/- cells to those of WT cells without rescuing 1,5-InsP8 levels. Attenuation of IP6K restored p53 expression but did not affect the hypermetabolic phenotype. Thus, we conclude that 5-InsP7 regulates p53 expression, whereas 1,5-InsP8 regulates ATP levels. These findings attribute hitherto unsuspected functionality for 1,5-InsP8 to bioenergetic homeostasis.

Clinical value of bedside abdominal sonography performed by certified sonographer in emergency evaluation of blunt abdominal trauma.

PURPOSE: To investigate the accuracy and efficiency of bedside ultrasonography application performed by certified sonographer in emergency patients with blunt abdominal trauma. METHODS: The study was carried out from 2017 to 2019. Findings in operations or on computed tomography (CT) were used as references to evaluate the accuracy of bedside abdominal ultrasonography. The time needed for bedside abdominal ultrasonography or CT examination was collected separately to evaluate the efficiency of bedside abdominal ultrasonography application. RESULTS: Bedside abdominal ultrasonography was performed in 106 patients with blunt abdominal trauma, of which 71 critical patients received surgery. The overall diagnostic accordance rate was 88.68%. The diagnostic accordance rate for liver injury, spleen injury, kidney injury, gut perforation, retroperitoneal hematoma and multiple abdominal organ injury were 100%, 94.73%, 94.12%, 20.00%, 100% and 81.48%, respectively. Among the 71 critical patients, the diagnostic accordance rate was 94.37%, in which the diagnostic accordance rate for liver injury, spleen injury, kidney injury, gut perforation and multiple abdominal organ injury were 100%, 100%, 100%, 20.00% and 100%. The mean time for imaging examination of bedside abdominal ultrasonography was longer than that for CT scan (4.45 ± 1.63 vs. 2.38 ± 1.19) min; however, the mean waiting time before examination (7.37 ± 2.01 vs. 16.42 ± 6.37) min, the time to make a diagnostic report (6.42 ± 3.35 vs. 36.26 ± 13.33) min, and the overall time (17.24 ± 2.33 vs. 55.06 ± 6.96) min were shorter for bedside abdominal ultrasonography than for CT scan. CONCLUSION: Bedside ultrasonography application provides both efficiency and reliability for the assessment of blunt abdominal trauma. Especially for patients with free peritoneal effusion and critical patients, bedside ultrasonography has been proved obvious advantageous. However, for negative bedside ultrasonography patients with blunt abdominal trauma, we recommend further abdominal CT scan or serial ultrasonography scans subsequently.

Structural and biochemical characterization of Siw14: A protein-tyrosine phosphatase fold that metabolizes inositol pyrophosphates.

Inositol pyrophosphates (PP-InsPs) are "energetic" intracellular signals that are ubiquitous in animals, plants, and fungi; structural and biochemical characterization of PP-InsP metabolic enzymes provides insight into their evolution, reaction mechanisms, and regulation. Here, we describe the 2.35-Å-resolution structure of the catalytic core of Siw14, a 5-PP-InsP phosphatase from Saccharomyces cerevisiae and a member of the protein tyrosine-phosphatase (PTP) superfamily. Conclusions that we derive from structural data are supported by extensive site-directed mutagenesis and kinetic analyses, thereby attributing new functional significance to several key residues. We demonstrate the high activity and exquisite specificity of Siw14 for the 5-diphosphate group of PP-InsPs. The three structural elements that demarcate a 9.2-Å-deep substrate-binding pocket each have spatial equivalents in PTPs, but we identify how these are specialized for Siw14 to bind and hydrolyze the intensely negatively charged PP-InsPs. (a) The catalytic P-loop with the CX5R(S/T) PTP motif contains additional, positively charged residues. (b) A loop between the α5 and α6 helices, corresponding to the Q-loop in PTPs, contains a lysine and an arginine that extend into the catalytic pocket due to displacement of the α5 helix orientation through intramolecular crowding caused by three bulky, hydrophobic residues. (c) The general-acid loop in PTPs is replaced in Siw14 with a flexible loop that does not use an aspartate or glutamate as a general acid. We propose that an acidic residue is not required for phosphoanhydride hydrolysis.

The Significance of the Bifunctional Kinase/Phosphatase Activities of Diphosphoinositol Pentakisphosphate Kinases (PPIP5Ks) for Coupling Inositol Pyrophosphate Cell Signaling to Cellular Phosphate Homeostasis.

Proteins responsible for Pi homeostasis are critical for all life. In Saccharomyces cerevisiae, extracellular [Pi] is "sensed" by the inositol-hexakisphosphate kinase (IP6K) that synthesizes the intracellular inositol pyrophosphate 5-diphosphoinositol 1,2,3,4,6-pentakisphosphate (5-InsP7) as follows: during a period of Pi starvation, there is a decline in cellular [ATP]; the unusually low affinity of IP6Ks for ATP compels 5-InsP7 levels to fall in parallel (Azevedo, C., and Saiardi, A. (2017) Trends. Biochem. Sci. 42, 219-231. Hitherto, such Pi sensing has not been documented in metazoans. Here, using a human intestinal epithelial cell line (HCT116), we show that levels of both 5-InsP7 and ATP decrease upon [Pi] starvation and subsequently recover during Pi replenishment. However, a separate inositol pyrophosphate, 1,5-bisdiphosphoinositol 2,3,4,6-tetrakisphosphate (InsP8), reacts more dramatically (i.e. with a wider dynamic range and greater sensitivity). To understand this novel InsP8 response, we characterized kinetic properties of the bifunctional 5-InsP7 kinase/InsP8 phosphatase activities of full-length diphosphoinositol pentakisphosphate kinases (PPIP5Ks). These data fulfil previously published criteria for any bifunctional kinase/phosphatase to exhibit concentration robustness, permitting levels of the kinase product (InsP8 in this case) to fluctuate independently of varying precursor (i.e. 5-InsP7) pool size. Moreover, we report that InsP8 phosphatase activities of PPIP5Ks are strongly inhibited by Pi (40-90% within the 0-1 mm range). For PPIP5K2, Pi sensing by InsP8 is amplified by a 2-fold activation of 5-InsP7 kinase activity by Pi within the 0-5 mm range. Overall, our data reveal mechanisms that can contribute to specificity in inositol pyrophosphate signaling, regulating InsP8 turnover independently of 5-InsP7, in response to fluctuations in extracellular supply of a key nutrient.

Bacillus anthracis Spore Surface Protein BclA Mediates Complement Factor H Binding to Spores and Promotes Spore Persistence.

Spores of Bacillus anthracis, the causative agent of anthrax, are known to persist in the host lungs for prolonged periods of time, however the underlying mechanism is poorly understood. In this study, we demonstrated that BclA, a major surface protein of B. anthracis spores, mediated direct binding of complement factor H (CFH) to spores. The surface bound CFH retained its regulatory cofactor activity resulting in C3 degradation and inhibition of downstream complement activation. By comparing results from wild type C57BL/6 mice and complement deficient mice, we further showed that BclA significantly contributed to spore persistence in the mouse lungs and dampened antibody responses to spores in a complement C3-dependent manner. In addition, prior exposure to BclA deletion spores (ΔbclA) provided significant protection against lethal challenges by B. anthracis, whereas the isogenic parent spores did not, indicating that BclA may also impair protective immunity. These results describe for the first time an immune inhibition mechanism of B. anthracis mediated by BclA and CFH that promotes spore persistence in vivo. The findings also suggested an important role of complement in persistent infections and thus have broad implications.

Correction: Bacillus anthracis Spore Surface Protein BclA Mediates Complement Factor H Binding to Spores and Promotes Spore Persistence.

[This corrects the article DOI: 10.1371/journal.ppat.1005678.].

Activation of the classical complement pathway by Bacillus anthracis is the primary mechanism for spore phagocytosis and involves the spore surface protein BclA.

Interactions between spores of Bacillus anthracis and macrophages are critical for the development of anthrax infections, as spores are thought to use macrophages as vehicles to disseminate in the host. In this study, we report a novel mechanism for phagocytosis of B. anthracis spores. Murine macrophage-like cell line RAW264.7, bone marrow-derived macrophages, and primary peritoneal macrophages from mice were used. The results indicated that activation of the classical complement pathway (CCP) was a primary mechanism for spore phagocytosis. Phagocytosis was significantly reduced in the absence of C1q or C3. C3 fragments were found deposited on the spore surface, and the deposition was dependent on C1q and Ca(2+). C1q recruitment to the spore surface was mediated by the spore surface protein BclA, as recombinant BclA bound directly and specifically to C1q and inhibited C1q binding to spores in a dose-dependent manner. C1q binding to spores lacking BclA (ΔbclA) was also significantly reduced compared with wild-type spores. In addition, deposition of both C3 and C4 as well as phagocytosis of spores were significantly reduced when BclA was absent, but were not reduced in the absence of IgG, suggesting that BclA, but not IgG, is important in these processes. Taken together, these results support a model in which spores actively engage CCP primarily through BclA interaction with C1q, leading to CCP activation and opsonophagocytosis of spores in an IgG-independent manner. These findings are likely to have significant implications on B. anthracis pathogenesis and microbial manipulation of complement.

IP8: A quantitatively minor inositol pyrophosphate signaling molecule that punches above its weight.

The inositol pyrophosphates (PP-IPs) are specialized members of the wider inositol phosphate signaling family that possess functionally significant diphosphate groups. The PP-IPs exhibit remarkable functionally versatility throughout the eukaryotic kingdoms. However, a quantitatively minor PP-IP - 1,5 bisdiphosphoinositol tetrakisphosphate (1,5-IP8) - has received considerably less attention from the cell signalling community. The main purpose of this review is to summarize recently-published data which have now brought 1,5-IP8 into the spotlight, by expanding insight into the molecular mechanisms by which this polyphosphate regulates many fundamental biological processes.

Homeostatic coordination of cellular phosphate uptake and efflux requires an organelle-based receptor for the inositol pyrophosphate IP8.

Phosphate (Pi) serves countless metabolic pathways and is involved in macromolecule synthesis, energy storage, cellular signaling, and bone maintenance. Herein, we describe the coordination of Pi uptake and efflux pathways to maintain mammalian cell Pi homeostasis. We discover that XPR1, the presumed Pi efflux transporter, separately supervises rates of Pi uptake. This direct, regulatory interplay arises from XPR1 being a binding partner for the Pi uptake transporter PiT1, involving a predicted transmembrane helix/extramembrane loop in XPR1, and its hitherto unknown localization in a subset of intracellular LAMP1-positive puncta (named "XLPVs"). A pharmacological mimic of Pi homeostatic challenge is sensed by the inositol pyrophosphate IP8, which functionalizes XPR1 to respond in a temporally hierarchal manner, initially adjusting the rate of Pi efflux, followed subsequently by independent modulation of PiT1 turnover to reset the rate of Pi uptake. These observations generate a unifying model of mammalian cellular Pi homeostasis, expanding opportunities for therapeutic intervention.

IL-17 family: cytokines, receptors and signaling.

The interleukin 17 (IL-17) family, a subset of cytokines consisting of IL-17A-F, plays crucial roles in host defense against microbial organisms and in the development of inflammatory diseases. Although IL-17A is the signature cytokine produced by T helper 17 (Th17) cells, IL-17A and other IL-17 family cytokines have multiple sources ranging from immune cells to non-immune cells. The IL-17 family signals via their correspondent receptors and activates downstream pathways that include NFκB, MAPKs and C/EBPs to induce the expression of anti-microbial peptides, cytokines and chemokines. The proximal adaptor Act1 is a common mediator during the signaling of all IL-17 cytokines so far and is thus involved in IL-17 mediated host defense and IL-17-driven autoimmune conditions. This review will give an overview and recent updates on the IL-17 family, the activation and regulation of IL-17 signaling as well as diseases associated with this cytokine family.

Nucleolar Architecture Is Modulated by a Small Molecule, the Inositol Pyrophosphate 5-InsP7.

Inositol pyrophosphates (PP-InsPs); are a functionally diverse family of eukaryotic molecules that deploy a highly-specialized array of phosphate groups as a combinatorial cell-signaling code. One reductive strategy to derive a molecular-level understanding of the many actions of PP-InsPs is to individually characterize the proteins that bind them. Here, we describe an alternate approach that seeks a single, collective rationalization for PP-InsP binding to an entire group of proteins, i.e., the multiple nucleolar proteins previously reported to bind 5-InsP7 (5-diphospho-inositol-1,2,3,4,6-pentakisphosphate). Quantitative confocal imaging of the outer nucleolar granular region revealed its expansion when cellular 5-InsP7 levels were elevated by either (a) reducing the 5-InsP7 metabolism by a CRISPR-based knockout (KO) of either NUDT3 or PPIP5Ks; or (b), the heterologous expression of wild-type inositol hexakisphosphate kinase, i.e., IP6K2; separate expression of a kinase-dead IP6K2 mutant did not affect granular volume. Conversely, the nucleolar granular region in PPIP5K KO cells shrank back to the wild-type volume upon attenuating 5-InsP7 synthesis using either a pan-IP6K inhibitor or the siRNA-induced knockdown of IP6K1+IP6K2. Significantly, the inner fibrillar volume of the nucleolus was unaffected by 5-InsP7. We posit that 5-InsP7 acts as an 'electrostatic glue' that binds together positively charged surfaces on separate proteins, overcoming mutual protein-protein electrostatic repulsion the latter phenomenon is a known requirement for the assembly of a non-membranous biomolecular condensate.

Capillary electrophoresis mass spectrometry identifies new isomers of inositol pyrophosphates in mammalian tissues.

Technical challenges have to date prevented a complete profiling of the levels of myo-inositol phosphates (InsPs) and pyrophosphates (PP-InsPs) in mammalian tissues. Here, we have deployed capillary electrophoresis mass spectrometry to identify and record the levels of InsPs and PP-InsPs in several tissues obtained from wild type mice and a newly created PPIP5K2 knockout strain. We observe that the mouse colon harbours unusually high levels of InsPs and PP-InsPs. Additionally, the PP-InsP profile is considerably more complex than previously reported for animal cells: using chemically synthesized internal stable isotope references and high-resolution mass spectra, we characterize two new PP-InsP isomers as 4/6-PP-InsP5 and 2-PP-InsP5. The latter has not previously been described in nature. The analysis of feces and the commercial mouse diet suggests that the latter is one potential source of noncanonical isomers in the colon. However, we also identify both molecules in the heart, indicating unknown synthesis pathways in mammals. We also demonstrate that the CE-MS method is sensitive enough to measure PP-InsPs from patient samples such as colon biopsies and peripheral blood mononuclear cells (PBMCs). Strikingly, PBMCs also contain 4/6-PP-InsP5 and 2-PP-InsP5. In summary, our study substantially expands PP-InsP biology in mammals.

Entry of Bacillus anthracis spores into epithelial cells is mediated by the spore surface protein BclA, integrin α2ß1 and complement component C1q.

Inhalational anthrax is initiated by pulmonary exposure to Bacillus anthracis spores. Spore entry into lung epithelial cells is observed both in vitro and in vivo and evidence suggests it is important for bacterial dissemination and virulence. However the specific host receptor and spore factor that mediate the entry process were unknown. Here, we report that integrin α2ß1 is a major receptor for spore entry. This is supported by results from blocking antibodies, siRNA knock-down, colocalization, and comparison of spore entry into cells that do or do not express α2. BclA, a major spore surface protein, is found to be essential for entry and α2ß1-mediated entry is dependent on BclA. However, BclA does not appear to bind directly to α2. Furthermore, spore entry into α2-expressing cells is dramatically reduced in the absence of serum, suggesting that additional factors are involved. Finally, complement component C1q, also an α2ß1 ligand, appears to act as a bridging molecule or a cofactor for BclA/α2ß1-mediated spore entry and BclA binds to C1q in a dose-dependent and saturable manner. These findings suggest a novel mechanism for pathogen entry into host cells as well as a new function for C1q-integrin interactions. The implications of these findings are discussed.

Development of Novel IP6K Inhibitors for the Treatment of Obesity and Obesity-Induced Metabolic Dysfunctions.

Obesity and obesity-induced metabolic dysfunctions are significant risk factors for nonalcoholic fatty liver disease and cardiovascular diseases. Thus, obesity is an economic and social burden in developed countries. Blocking the synthesis of inositol pyrophosphates by inositol hexakisphosphate kinase (IP6K) has been identified as a potential therapeutic strategy for obesity and related diseases. We have developed a novel and potent IP6K inhibitor 20 (UNC7467) (IC50 values: IP6K1 8.9 nM; IP6K2 4.9 nM; IP6K3 1320 nM). Inositol phosphate profiling of the HCT116 colon cancer cell line demonstrates that 20 reduced levels of inositol pyrophosphates by 66-81%, without significantly perturbing levels of other inositol phosphates. Furthermore, intraperitoneal injection of 20 in diet-induced obese mice improved glycemic profiles, ameliorated hepatic steatosis, and reduced weight gain without altering food intake. Thus, inhibitor 20 can be used as an in vivo probe for IP6K-related research. Moreover, it may have therapeutic relevance in treating obesity and related diseases.

A two-way switch for inositol pyrophosphate signaling: Evolutionary history and biological significance of a unique, bifunctional kinase/phosphatase.

The inositol pyrophosphates (PP-InsPs) are a unique subgroup of intracellular signals with diverse functions, many of which can be viewed as reflecting an overarching role in metabolic homeostasis. Thus, considerable attention is paid to the enzymes that synthesize and metabolize the PP-InsPs. One of these enzyme families - the diphosphoinositol pentakisphosphate kinases (PPIP5Ks) - provides an extremely rare example of separate kinase and phosphatase activities being present within the same protein. Herein, we review the current state of structure/function insight into the PPIP5Ks, the separate specialized activities of the two metazoan PPIP5K genes, and we describe a phylogenetic analysis that places PPIP5K evolutionary origin within the Excavata, the very earliest of eukaryotes. These different aspects of PPIP5K biology are placed in the context of a single, overriding question. Why are they bifunctional: i.e., what is the particular significance of the ability to turn PP-InsP signaling on or off from two separate 'switches' in a single protein?