Does interleukin-1 affect intracellular calcium in osteoblast-like cells (UMR-106)?

Identifying Novel Susceptibility Genes for Colorectal Cancer Risk From a Transcriptome-Wide Association Study of 125,478 Subjects

BACKGROUND AND AIMS

Susceptibility genes and the underlying mechanisms for the majority of risk loci identified by genome-wide association studies (GWAS) for colorectal cancer (CRC) risk remain largely unknown. We conducted a transcriptome-wide association study (TWAS) to identify putative susceptibility genes.

METHODS

Gene-expression prediction models were built using transcriptome and genetic data from the 284 normal transverse colon tissues of European descendants from the Genotype-Tissue Expression (GTEx), and model performance was evaluated using data from The Cancer Genome Atlas (n = 355). We applied the gene-expression prediction models and GWAS data to evaluate associations of genetically predicted gene-expression with CRC risk in 58,131 CRC cases and 67,347 controls of European ancestry. Dual-luciferase reporter assays and knockdown experiments in CRC cells and tumor xenografts were conducted.

RESULTS

We identified 25 genes associated with CRC risk at a Bonferroni-corrected threshold of P < 9.1 × 10-6, including genes in 4 novel loci, PYGL (14q22.1), RPL28 (19q13.42), CAPN12 (19q13.2), MYH7B (20q11.22), and MAP1L3CA (20q11.22). In 9 known GWAS-identified loci, we uncovered 9 genes that have not been reported previously, whereas 4 genes remained statistically significant after adjusting for the lead risk variant of the locus. Through colocalization analysis in GWAS loci, we additionally identified 12 putative susceptibility genes that were supported by TWAS analysis at P < .01. We showed that risk allele of the lead risk variant rs1741640 affected the promoter activity of CABLES2. Knockdown experiments confirmed that CABLES2 plays a vital role in colorectal carcinogenesis.

CONCLUSIONS

Our study reveals new putative susceptibility genes and provides new insight into the biological mechanisms underlying CRC development.

Differential effects of Fe2+ and Fe3+ on osteoblasts and the effects of 1,25(OH)2D3, deferiprone and extracellular calcium on osteoblast viability under iron-overloaded conditions

One of the potential contributing factors for iron overload-induced osteoporosis is the iron toxicity on bone forming cells, osteoblasts. In this study, the comparative effects of Fe³⁺ and Fe²⁺ on osteoblast differentiation and mineralization were studied in UMR-106 osteoblast cells by using ferric ammonium citrate and ferrous ammonium sulfate as Fe³⁺ and Fe²⁺ donors, respectively. Effects of 1,25 dihydroxyvitamin D₃ [1,25(OH)₂D₃] and iron chelator deferiprone on iron uptake ability of osteoblasts were examined, and the potential protective ability of 1,25(OH)₂D₃, deferiprone and extracellular calcium treatment in osteoblast cell survival under iron overload was also elucidated. The differential effects of Fe³⁺ and Fe²⁺ on reactive oxygen species (ROS) production in osteoblasts were also compared. Our results showed that both iron species suppressed alkaline phosphatase gene expression and mineralization with the stronger effects from Fe³⁺ than Fe²⁺. 1,25(OH)₂D₃ significantly increased the intracellular iron but minimally affected osteoblast cell survival under iron overload. Deferiprone markedly decreased intracellular iron in osteoblasts, but it could not recover iron-induced osteoblast cell death. Interestingly, extracellular calcium was able to rescue osteoblasts from iron-induced osteoblast cell death. Additionally, both iron species could induce ROS production and G0/G1 cell cycle arrest in osteoblasts with the stronger effects from Fe³⁺. In conclusions, Fe³⁺ and Fe²⁺ differentially compromised the osteoblast functions and viability, which can be alleviated by an increase in extracellular ionized calcium, but not 1,25(OH)₂D₃ or iron chelator deferiprone. This study has provided the invaluable information for therapeutic design targeting specific iron specie(s) in iron overload-induced osteoporosis. Moreover, an increase in extracellular calcium could be beneficial for this group of patients.

The production of nitric oxide and prostaglandin E(2) by primary bone cells is shear stress dependent

Loading-induced flow of interstitial fluid through the lacuno-canalicular network is a likely signal for bone cell adaptive responses. However, the nature of the stimulus that activates the cell is debated. Candidate stimuli include wall shear stress, streaming potentials, and chemotransport. We have addressed the nature of the flow-derived cell stimulus by comparing variations in fluid transport with variations in wall shear stress, using nitric oxide (NO) and prostaglandin E(2) (PGE(2)) production as a parameter of bone cell activation. Adult mouse long bone cell cultures were treated for 15min with or without pulsating fluid flow using the following regimes: Low PFF, mean flow rate 0.20 cm(3)/s, 3 Hz, shear stress 0.4+/-0.12 Pa; Medium PFF, 0.33 cm(3)/s, 5 Hz, 0.6+/-0.27 Pa; and High PFF, 0.63 cm(3)/s, 9Hz, 1.2+/-0.37 Pa. In some Low PFF experiments, 2.8% neutral dextran (mol. wt. 4.98x10(4)) was added to the flow medium to increase the viscosity, thereby increasing the wall shear stress 3-fold to a level similar of the High PFF stimulus, but without affecting streaming potentials or chemotransport. NO and PGE(2) production were stimulated by Low, Medium, and High PFF in a dose-dependent manner. Application of Low PFF using dextran-supplemented medium, enhanced both the NO and PGE(2) response by 3-fold, to a level mimicking the response to High PFF at normal viscosity. These results show that the production of NO and PGE(2) by bone cells can be enhanced in a dose-dependent manner by fluid flow of increasing wall shear stress. Therefore, the stimulus leading to NO and PGE(2) production is the flow-derived shear stress, and not streaming potentials or chemotransport.

Interleukin-4 reversed the Interleukin-1-inhibited proteoglycan synthesis through the inhibition of NO release: a possible involvement of intracellular calcium ion

Interleukin-1 (IL-1) causes cartilage degradation through nitric oxide (NO) synthesis. Although Interleukin-4 (IL-4) antagonizes the IL-1-mediated cartilage degradation, the precise mechanisms are not clear. We examined the effect of IL-4 on NO synthesis in parallel with intracellular Ca levels ([Ca(2+)]i) and proteoglycan (PG) synthesis. IL-4-inhibited IL-1-enhanced NO release in a dose-dependent manner. IL-1-enhanced [Ca(2+)]i in the chondrocytes, and IL-4 attenuated this increase. IL-4 reversed IL-1-inhibited PG synthesis. Accordingly, IL-4 reversed the IL-1-inhibited PG synthesis through the inhibition of NO release. An increase in [Ca(2+)]i with IL-1 is possibly involved in this action.

IL-1beta increases intracellular calcium through an IL-1 type 1 receptor mediated mechanism in C6 astrocytic cells

Interleukin-1beta (IL-1beta) is a cytokine that regulates a variety of biological processes. In addition to its traditional role in the immune system, IL-1beta plays an integral role in neural-immune and developmental processes in the nervous system. The pleiotropic ability of IL-1beta may be due to the activation of different signal transduction mechanisms in specific cell types or under certain cellular conditions. We have previously demonstrated that IL- regulates healing and repair in the developing, mammalian nervous system. In the damaged perinatal mouse brain, IL-1beta is expressed in astrocytes that change from a stellate to a spindle-shaped morphology. The spindle-shaped astrocytes enclose the wound, separating the healthy from damaged neural tissue. The shape change and subsequent repair processes are IL-1beta activity-dependent, acting through the IL-1 type 1 receptor (IL-1R1), as co-application of the IL-1type 1 receptor antagonist protein (IL-1ra) blocks IL-1beta induced effects. In the C6 astrocytic cell line, IL-1beta induced similar shape changes and upregulated expression of the cytoskeletal protein, glial fibrillary acidic protein (GFAP). Since cytoskeletal changes, as well as specific signal transduction mechanisms, are associated with increases in intracellular calcium ([Ca2+]i), studies were carried out to determine if increases in [Ca2+]i induced by IL-1beta occurred through activation of the IL-1R1 in C6 cells. Cells were treated with IL-1beta and/or IL-1ra, followed by measurement of relative changes in [Ca2+]i using fura-2 fluorescence imaging methods. IL-1beta increased [Ca2+]i levels in a dose and time dependent manner. Treatment with IL-1ra blocked IL-1beta induced increases in [Ca2+]i, indicating that IL-1beta acts through the IL-1R1. Immunocytochemistry experiments showed that untreated C6 cells normally express IL-1beta, IL-1ra, and IL-1RI. Thus, IL-1 system molecules may play a role in normal C6 astrocyte physiology.

Interleukin 1-induced calcium signalling in chondrocytes requires focal adhesions

The cytokine interleukin 1 (IL-1) is an important mediator of connective-tissue destruction in arthritic joints but the mechanisms by which IL-1 mediates signal transduction in chondrocytes is poorly understood. Previous results have indicated that IL-1 receptors co-localize with focal adhesions [Qwarnstrom, Page, Gillis and Dower (1988) J. Biol. Chem. 263, 8261-8269], discrete adhesive domains of cells that function in cell attachment and possibly in signal transduction. We have determined whether focal adhesions restrict IL-1-induced Ca2+ signalling in primary cultures of bovine chondrocytes. In cells grown for 24 h on fibronectin, the basal intracellular Ca2+ ion concentration ([Ca2+]i) was 100+/-3 nM. Optimal increases of [Ca2+]i above baseline were induced by 10 nM IL-1 (183+/-30 nM above baseline). There was no significant difference between cells plated on fibronectin or type II collagen (P>0.2; 233+/-90 nM above baseline). Ca2+ transients were significantly decreased by the inclusion of 0.5 mM EGTA in the bathing buffer (74+/-11 nM above baseline), and 1 microM thapsigargin completely blocked Ca2+ transients. Cells plated on poly-(l-lysine) or suspended cells showed no Ca2+ increases, whereas cells grown on fibronectin exhibited IL-1-induced Ca2+ responses that corresponded temporally to the time-dependent cell spreading after plating on fibronectin. Cells plated on poly-(l-lysine) and incubated with fibronectin-coated beads exhibited vinculin staining in association with the beads. In identical cell preparations, IL-1 induced a 136+/-39 nM increase of [Ca2+]i above baseline in response to 10 nM IL-1beta. There were no IL-1-induced Ca2+ increases when cells on poly-(l-lysine) were incubated with fibronectin-coated beads for only 15 min at 37 degrees C, in cells maintained for 3 h at 4 degrees C, in cells incubated with BSA beads for 3 h at 37 degrees C, or in cells pretreated with cytochalasin D. Labelling of IL-1 receptors with 125I-IL-1beta showed 3-fold more specific labelling of focal adhesion complexes in cells incubated with fibronectin-coated beads compared with cells incubated with BSA-coated beads, indicating that IL-1 receptor binding or the number of IL-1 receptors was increased in focal adhesions. These results indicate that, in chondrocytes, IL-1-induced Ca2+ signalling is dependent on focal adhesion formation and that focal adhesions recruit IL-1 receptors by redistribution in the cell membrane.

Interleukin-1-induced calcium flux in human fibroblasts is mediated through focal adhesions

Interleukin-1 (IL-1) is an important mediator of inflammation and also modulates fibroblast metabolism. To assess mechanisms of IL-1-induced signal transduction and calcium flux, early passage human fibroblasts were loaded with fura2/AM. Cells grown on coverslips exhibited dose-dependent [Ca2+]i responses that were maximal at 10(-8) M IL-1 beta with time to maximum flux of 50 s. Cells incubated with anti-Type 1-IL-1 receptor antibody exhibited a 45 nM increase in [Ca2+]i above baseline but demonstrated no calcium response after IL-1 beta treatment. Incubation with EGTA (5 mM) or thapsigargin (1 microM) caused 75% and 37% reductions, respectively, in the IL-1-induced [Ca2+]i increase, suggesting that extracellular Ca2+ predominates in IL-1-stimulated calcium flux. Cells in suspension did not exhibit [Ca2+]i responses to IL-1 beta. The relationship between [Ca2+]i signaling and focal adhesions was examined by plating cells on fibronectin or poly-L-lysine, conditions that either permitted or blocked the formation of focal adhesions. Cells on fibronectin exhibited co-distribution of immunostaining for talin, vinculin, IL-1 receptor, and focal adhesion kinase (pp125fak) in focal adhesions and demonstrated [Ca2+]i responses with 10(-8) M IL-1 beta. Cells on poly-L-lysine or cells in suspension did not exhibit co-distribution of pp125fak, IL-1 receptor, and focal adhesion proteins and did not exhibit calcium flux. The dependence of IL-1-stimulated [Ca2+]i responses on tyrosine kinases was examined first by treating cells with genistein, a selective inhibitor of tyrosine kinases. Genistein (100 microM) completely blocked [Ca2+]i responses to 10(-8) M IL-1, whereas its inactive analogue genistin was not inhibitory. Second, fibroblasts lysates were immunoprecipitated with an antiphosphotyrosine antibody and the lysates were Western-blotted with an anti-pp125fak antibody. Cells grown on fibronectin and stimulated with IL-1 exhibited tyrosine phosphorylation of pp125fak whereas untreated cells or cells grown on poly-L-lysine and treated with IL-1 showed no reaction. Fibroblasts electroinjected with anti-pp125fak monoclonal antibody showed no [Ca2+], response, whereas cells treated with an irrelevant antibody exhibited a normal [Ca2+]i response. Collectively, these data indicate that fibroblasts require substrate attachment and clustering of IL-1 receptors to focal adhesions for IL-1-induced [Ca2+]i responses. Calcium fluxes are mediated through tyrosine kinases whose substrates include pp125fak. These studies therefore demonstrate that activation of intracellular signaling pathways by IL-1 is dependent on IL-1 receptor-cytoskeletal protein interactions.

Interleukin-1 selectively potentiates bradykinin-stimulated arachidonic acid release from human synovial fibroblasts

Exposure of human synovial fibroblasts prelabelled with [3H]arachidonic acid to bradykinin causes a rapid and sustained increase in arachidonic acid release, a transient increase in cytosolic calcium and an increase in radiolabelled diacylglycerol. Activation of arachidonic acid release by bradykinin was potentiated by interleukin-1 added either simultaneously with bradykinin or to cultures 24 h before addition of bradykinin. In contrast, interleukin-1 did not modify bradykinin-induced increases in cytosolic calcium or diacylglycerol. The stimulation of arachidonic acid release in response to bradykinin, in the absence or presence of interleukin-1, was not affected by RHC-80267, an inhibitor of diacylglycerol kinase, suggesting that deacylation of diacylglycerol was not an important pathway of arachidonic acid production in cultures exposed to bradykinin. This conclusion is supported by the observation that increased release of arachidonic acid was not accompanied by increased release of [14C]stearic acid in cultures labelled with both isotopes. Bradykinin-stimulated release of arachidonic acid was prevented by down-regulating protein kinase C by pretreatment with phorbol 12-myristate 13-acetate and was unaffected by inhibitors of protein synthesis actinomycin D or cycloheximide. On the other hand, interleukin-1 amplification of bradykinin-stimulated release of arachidonic acid was blocked by actinomycin D and cycloheximide. The results from this study point to activation of phospholipase A2 as the source of arachidonic acid in response to bradykinin. Our data further indicate that interleukin-1 selectively potentiates bradykinin activation of a phospholipase A2 by a mechanism requiring protein synthesis, but has no effect on bradykinin activation of phospholipase C.

Pertussis toxin-sensitive activation of phospholipase A2 can be resolved from phosphoinositidase C in primary cultures of mouse osteoblasts using indomethacin

Recent work has established that various bone-resorbing hormones are able to activate phosphoinositide metabolism as well as eicosanoid production in osteoblast-like cells, although the relationship between these pathways is unclear. We used pertussis toxin and indomethacin to inhibit the stimulation of [3H]arachidonic acid release and [3H]phosphoinositide turnover caused by treating primary cultures of mouse osteoblasts with fetal calf serum. We found (1) that pertussis toxin and indomethacin each inhibited both pathways and (2) that although pertussis toxin inhibited [3H]arachidonic acid release to a greater extent than indomethacin, [3H]inositol phosphate accumulation was inhibited rather more effectively by indomethacin. These data suggest that whereas ligands in fetal calf serum activate [3H]arachidonic acid release largely directly via the action of a pertussis-sensitive G protein, activation of phosphoinositidase C is indirect, being substantially dependent upon eicosanoid production. These experiments suggest that serial activation of phospholipase A2 and phosphoinositidase C may occur in osteoblasts and that only the former enzyme is regulated by a pertussis toxin-sensitive G protein.

Interleukin-1 beta enhances the response of human articular chondrocytes to extracellular ATP

It has been observed that both interleukin-1 (IL-1) and extracellular ATP stimulate the production of prostaglandin E (PGE) by human articular chondrocytes in monolayer culture. The combined effects of recombinant human IL-1 beta and ATP were therefore studied using these cells. IL-1 beta rapidly enhanced the response to a maximally effective concentration of ATP (100 microM). On continuous exposure of the cells to the cytokine, its effect was greatest after approx. 24 h and tended to decline thereafter. The enhancement of the response to 100 microM ATP by IL-1 beta was dose-dependent. Removal of IL-1 beta prior to treating the cells with 100 microM ATP did not affect the degree of enhancement of the response. The effect of the cytokine on the response to suboptimal concentrations of extracellular ATP was also tested. IL-1 beta lowered the minimum concentration of ATP required to elicit an increase in the production of PGE by human articular chondrocytes. These findings are of interest, since they indicate a synergistic interaction between a cytokine and a purinergic agonist. Moreover, since both the sensitivity of the cells to extracellular ATP and the maximum response to this agent were enhanced, it is possible that IL-1 modulates more than one step in the process of P2-purinoceptor-mediated stimulation of PGE production. These observations may be relevant to the pathogenesis of some forms of arthritis.

Comparison of human interleukin-1 beta and its 163-171 peptide in bone resorption and the immune response

Human interleukin-1 beta (IL-1 beta) caused a dose- and time-dependent enhancement of the release of 45Ca from prelabeled mouse calvaria in organ culture. In addition, IL-1 beta dose-dependently stimulated the formation of prostaglandin E2 (PGE2) and 6-keto-PGF1 alpha in the calvarial bones. However, IL-1 beta-induced 45Ca release was only partially inhibited by blocking the PGE2 response with indomethacin, suggesting that enhanced PGE2 formation in response to IL-1 beta is not necessary to obtain a bone resorptive effect, but that prostaglandins potentiate the action of IL-1 beta. The synthetic nonapeptide VQGEESNDK, corresponding to the fragment 163-171 of human IL-1 beta, administered simultaneously with antigen (SRBC) to C3H/HeN male mice, induced a dose-dependent enhancement of specific antibody-producing cells in the spleen (PFC). The degree of PFC stimulation was comparable to that caused by native human IL-1 beta. In mouse bone cultures, neither 45Ca release nor prostanoid formation was stimulated by fragment 163-171. These data indicate that (1) IL-1 beta-induced stimulation of bone resorption is dissociable from IL-1 beta-induced increase of prostanoid biosynthesis and (2) the epitope of the IL-1 beta molecule involved in the immunostimulatory effects may be different from that involved in the stimulatory effects on bone resorption.

Physiological and pharmacological regulation of biological calcification

Biological calcification is a highly regulated process which occurs in diverse species of microorganisms, plants, and animals. Calcification provides tissues with structural rigidity to function in support and protection, supplies the organism with a reservoir for physiologically important ions, and also serves in a variety of specialized functions. In the vertebrate skeleton, hydroxyapatite crystals are laid down on a backbone of type I collagen, with the process being controlled by a wide range of noncollagenous proteins present in the local surroundings. In bone, cells of the osteoblast lineage are responsible for the synthesis of the bone matrix and many of these regulatory proteins. Osteoclasts, on the other hand, are continually resorbing bone to both produce changes in bone shape and maintain skeletal integrity, and to establish the ionic environment needed by the organism. The proliferation, differentiation, and activity of these cells is regulated by a number of growth factors and hormones. While much has already been discovered over the past few years about the involvement of various regulators in the process of mineralization, the identification and functional characterization of these factors remains an area of intense investigation. As with any complex, biological system that is in a finely tuned equilibrium under normal conditions, problems can occur. An imbalance in the processes of formation and resorption can lead to calcification disorders, and the resultant diseases of the skeletal system have a major impact on human health. A number of pharmacological agents have been, and are being, investigated for their therapeutic potential to correct these defects.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-1 stimulates diglyceride accumulation in the absence of protein kinase C activation

Despite advances in the knowledge of the intracellular signalling in response to extracellular messengers, the mechanism of action of interleukin-1 (IL-1) has remained an enigma. In the present study, we have employed human dermal fibroblasts (Detroit 532 cells) to investigate IL-1 beta-induced changes in intracellular signals. Both recombinant human IL-1 beta and a native preparation purified from human placental tissue were employed. Cyclic AMP levels in cell monolayers were unaltered by IL-1 beta. Also, IL-1 beta did not influence significantly the levels of phosphatidylinositol, phosphatidylinositol 4-monophosphate, and phosphatidylinositol 4,5-bisphosphate in the membrane, nor the water-soluble inositol phosphates, inositol monophosphate, inositol bisphosphate and inositol trisphosphate, in cells prelabelled with myo-[3H]inositol. In addition, intracellular calcium as measured by Quin2 was unaffected by interleukin-1. However, in cells labelled with [3H]glycerol or [3H]arachidonic acid, IL-1 beta caused an immediate rise in diglyceride (DG) accumulation. As the effects of IL-1 beta have been reported to be mimicked by tumour-promoting phorbol esters, this rise in DG suggested the involvement of protein kinase C (PKC). However, repeated experiments failed to reveal any acute effect of IL-1 beta on the activity of this enzyme. Furthermore, IL-1 beta did not cause the translocation of PKC between the membrane and the cytosol as has been found in response to other extracellular signals. Rather, IL-1 beta appeared to increase the synthesis of PKC in both membrane and cytosol preparations, an effect which could be prevented by coincubation with cycloheximide. These findings suggest that the diglyceride formed in response to IL-1 beta does not activate protein kinase C.

Interleukin 1 interacts synergistically with forskolin and isobutylmethylxanthine in stimulating bone resorption in organ culture

This study examined the interaction of interleukin 1 (IL-1) with forskolin and isobutyl-methylxanthine (3-isobutyl-1-methyl-xanthine) (IBMX) in stimulating bone resorption in 5-day fetal rat long bone organ culture. Forskolin and IBMX are pharmacologic agents that elevate cyclic adenosine monophosphate (AMP) levels in many cell types, including osteoblasts and osteoclasts. The interaction of IL-1 with forskolin and IBMX are synergistic when submaximal resorptive concentrations of agonists were examined. Stimulated resorption was 2 to 5 times that expected for an additive response. When maximally resorptive concentrations of agonists were examined, the interaction between IL-1 and the other agents was, at most, additive. We have previously reported that parathyroid hormone and prostaglandin E, agents that also activate the cyclic AMP pathway in bone cells, interact synergistically with IL-1 in stimulating bone resorption. The results of this study, together with our previous studies, suggest that activation of the cyclic AMP pathway is a sufficient signal for an agent to interact synergistically with IL-1 in stimulating bone resorption.