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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-IP 8) – 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-IP 8 into the spotlight, by expanding insight into the molecular mechanisms by which this polyphosphate regulates many fundamental biological processes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The HCT116 cell line, which has a pseudo-diploid karotype, is a popular model in the fields of cancer cell biology, intestinal immunity, and inflammation. In the current study, we describe two batches of diverged HCT116 cells, which we designate as HCT116NIH and HCT116UCL. Using both gel electrophoresis and HPLC, we show that HCT116UCL cells contain 6-fold higher levels of InsP8 than HCT116NIH cells. This observation is significant because InsP8 is one of a group of molecules collectively known as ‘inositol pyrophosphates’ (PP-InsPs)—highly ‘energetic’ and conserved regulators of cellular and organismal metabolism. Variability in the cellular levels of InsP8 within divergent HCT116 cell lines could have impacted the phenotypic data obtained in previous studies. This difference in InsP8 levels is more remarkable for being specific; levels of other inositol phosphates, and notably InsP6 and 5-InsP7, are very similar in both HCT116NIH and HCT116UCL lines. We also developed a new HPLC procedure to record 1-InsP7 levels directly (for the first time in any mammalian cell line); 1-InsP7 comprised <2% of total InsP7 in HCT116NIH and HCT116UCL lines. The elevated levels of InsP8 in the HCT116UCL lines were not due to an increase in expression of the PP-InsP kinases (IP6Ks and PPIP5Ks), nor to a decrease in the capacity to dephosphorylate InsP8. We discuss how the divergent PP-InsP profiles of the newly-designated HCT116NIH and HCT116UCL lines should be considered an important research opportunity: future studies using these two lines may uncover new features that regulate InsP8 turnover, and may also yield new directions for studying InsP8 function. [ABSTRACT FROM AUTHOR]

Highlights: [•] IL-17 is essential for host defense against microbial pathogens. [•] IL-17 signaling is tightly controlled at different levels of the signaling cascade. [•] Things can go wrong: pathogenic roles of IL-17 in autoimmunity. [•] IL-17 contributes to intestinal inflammation and tumorigenesis. [•] IL-17E potentiates type 2 allergic responses. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

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 α2β1 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 α2β1-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 α2β1 ligand, appears to act as a bridging molecule or a cofactor for BclA/α2β1-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. [ABSTRACT FROM AUTHOR]

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? [ABSTRACT FROM AUTHOR]

Keratoconus (KC) is the most common corneal ectatic disorder affecting >300,000 people in the US. KC normally has its onset in adolescence, progressively worsening through the third to fourth decades of life. KC patients report significant impaired vision-related quality of life. Genetic factors play an important role in KC pathogenesis. To identify novel genes in familial KC patients, we performed whole exome and genome sequencing in a four-generation family. We identified potential variants in the PPIP5K2 and PCSK1 genes. Using in vitro cellular model and in vivo gene-trap mouse model, we found critical evidence to support the role of PPIP5K2 in normal corneal function and KC pathogenesis. The gene-trap mouse showed irregular corneal surfaces and pathological corneal thinning resembling KC. For the first time, we have integrated corneal tomography and pachymetry mapping into characterization of mouse corneal phenotypes which could be widely implemented in basic and translational research for KC diagnosis and therapy in the future. [ABSTRACT FROM AUTHOR]

The inositol pyrophosphates (diphosphoinositol polyphosphates), which include 1-InsP 7 , 5-InsP 7 , and InsP 8 , are highly ‘energetic’ signaling molecules that play important roles in many cellular processes, particularly with regards to phosphate and bioenergetic homeostasis. Two classes of kinases synthesize the PP-InsPs: IP6Ks and PPIP5Ks. The significance of the IP6Ks - and their 5-InsP 7 product - has been widely reported. However, relatively little is known about the biological significance of the PPIP5Ks. The purpose of this review is to provide an update on developments in our understanding of key features of the PPIP5Ks, which we believe strengthens the hypothesis that their catalytic activities serve important cellular functions. Central to this discussion is the recent discovery that the PPIP5K is a rare example of a single protein that catalyzes a kinase/phosphatase futile cycle. [ABSTRACT FROM AUTHOR]

A correction to the article "Bacillus anthracis Spore Surface Protein BclA Mediates Complement Factor H Binding to Spores and Promotes Spore Persistance" that was published in the previous issue is presented.

A correction to the article "Bacillus anthracis Spore Surface Protein BclA Mediates Complement Factor H Binding to Spores and Promotes Spore Persistence" by Yanyu Wang and colleagues is presented.

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. [ABSTRACT FROM AUTHOR]

Diphosphoinositol pentakisphosphate (IP 7 ) is critical for the exocytotic capacity of the pancreatic β-cell, but its regulation by the primary instigator of β-cell exocytosis, glucose, is unknown. The high K m for ATP of the IP 7 -generating enzymes, the inositol hexakisphosphate kinases (IP6K1 and 2) suggests that these enzymes might serve as metabolic sensors in insulin secreting β-cells and act as translators of disrupted metabolism in diabetes. We investigated this hypothesis and now show that glucose stimulation, which increases the ATP/ADP ratio, leads to an early rise in IP 7 concentration in β-cells. RNAi mediated knock down of the IP6K1 isoform inhibits both glucose-mediated increase in IP 7 and first phase insulin secretion, demonstrating that IP6K1 integrates glucose metabolism and insulin exocytosis. In diabetic mouse islets the deranged ATP/ADP levels under both basal and glucose-stimulated conditions are mirrored in both disrupted IP 7 generation and insulin release. Thus the unique metabolic sensing properties of IP6K1 guarantees appropriate concentrations of IP 7 and thereby both correct basal insulin secretion and intact first phase insulin release. In addition, our data suggest that a specific cell signaling defect, namely, inappropriate IP 7 generation may be an essential convergence point integrating multiple metabolic defects into the commonly observed phenotype in diabetes. [ABSTRACT FROM AUTHOR]

The colon epithelium undergoes constant self-renewal in order to maintain its function as a nutrient sensor and a physical barrier from the commensal microbiota. Colon epithelium homeostasis is altered by inflammation and tissue injury/repair. In excess of which, contributes to the development of colon cancer. Here, we investigated the impact of IL-17A on the colon epithelium homeostasis and tumor development. IL-17A signals through a heterodimeric receptor complex composed of IL-17RA and IL-17RC. We found that the colon epithelium from IL-17RC-deficient mice displayed reduced proliferation, increased cell apoptosis and increased permeability after DSS challenge compared to control mice. Moreover, the IL-17RC-deficient mice developed significantly fewer colonic tumors compared to control mice in the AOM/DSS model of colitis-associated cancer. We then aimed to identify the cell-type responsible for IL-17A-mediated impact on homeostasis and tumorigenesis. Presumably, this IL-17-responsive cell population would sustain the initial mutation induced by carcinogen AOM, self replicate, and ultimately give rise to the neoplastic foci. Since the renewal of the colon epithelium relies upon a stem-cell niche (LGR5-positive cells) at the base of each crypt, we specifically ablated IL-17 signaling by deleting the IL-17R adaptor protein Act1 from this compartment. Following the AOM/DSS regimen the Act1CSC-KO mice developed significantly fewer colonic tumors compared to littermates. Mechanistically, IL-17A induced the activation of ERK5, ERK1/2 and JNK in colon epithelial cells. The activation of ERK5 and ERK1/2 were diminished in colon tissues of IL-17RC-deficient mice compared to that in the control mice with or without DSS treatment, implicating these MAPKs in IL-17R-dependent colon epithelium homeostasis. Furthermore, this pathway relied upon IL-17RC-dependent Act1 recruitment of TRAF4. We propose that IL-17R-Act1-TRAF4 cascade activates MAPKs in the LGR5-positive stem cells to promote regeneration after injury, consequently contributing to colon tumorigenesis by sustaining stem cells harboring a critical genetic lesion. [ABSTRACT FROM AUTHOR]