Pancreatic islet cells express BST-1, a CD38-like surface molecule having ADP-ribosyl cyclase activity

CD38–Cyclic ADP-Ribose Signal System in Physiology, Biochemistry, and Pathophysiology

Calcium (Ca²⁺) is a ubiquitous and fundamental signaling component that is utilized by cells to regulate a diverse range of cellular functions, such as insulin secretion from pancreatic β-cells of the islets of Langerhans. Cyclic ADP-ribose (cADPR), synthesized from NAD⁺ by ADP-ribosyl cyclase family proteins, such as the mammalian cluster of differentiation 38 (CD38), is important for intracellular Ca²⁺ mobilization for cell functioning. cADPR induces Ca²⁺ release from endoplasmic reticulum via the ryanodine receptor intracellular Ca²⁺ channel complex, in which the FK506-binding protein 12.6 works as a cADPR-binding regulatory protein. Recently, involvements of the CD38-cADPR signal system in several human diseases and animal models have been reported. This review describes the biochemical and molecular biological basis of the CD38-cADPR signal system and the diseases caused by its abnormalities.

Ectonucleotidases in Blood Malignancies: A Tale of Surface Markers and Therapeutic Targets

Leukemia develops as the result of intrinsic features of the transformed cell, such as gene mutations and derived oncogenic signaling, and extrinsic factors, such as a tumor-friendly, immunosuppressed microenvironment, predominantly in the lymph nodes and the bone marrow. There, high extracellular levels of nucleotides, mainly NAD⁺ and ATP, are catabolized by different ectonucleotidases, which can be divided in two families according to substrate specificity: on one side those that metabolize NAD⁺, including CD38, CD157, and CD203a; on the other, those that convert ATP, namely CD39 (and other ENTPDases) and CD73. They generate products that modulate intracellular calcium levels and that activate purinergic receptors. They can also converge on adenosine generation with profound effects, both on leukemic cells, enhancing chemoresistance and homing, and on non-malignant immune cells, polarizing them toward tolerance. This review will first provide an overview of ectonucleotidases expression within the immune system, in physiological and pathological conditions. We will then focus on different hematological malignancies, discussing their role as disease markers and possibly pathogenic agents. Lastly, we will describe current efforts aimed at therapeutic targeting of this family of enzymes.

ICCS/ESCCA consensus guidelines to detect GPI-deficient cells in paroxysmal nocturnal hemoglobinuria (PNH) and related disorders part 3 - data analysis, reporting and case studies

Over the past several years, a diverse group of physicians and other laboratory scientists have developed various recommendations and guidelines regarding best practices for PNH testing. This manuscript is based on these previous recommendations as well as various other relevant publications of experts in the area of PNH testing. The goal is to provide flow cytometry laboratories with an updated consensus approach to analysis and reporting of PNH results and to address the most common analytical challenges for accurate reporting of this rare disease. A comprehensive case library is included in this section. © 2017 International Clinical Cytometry Society.

CD157: From immunoregulatory protein to potential therapeutic target

CD157/BST1 glycosylphosphatidylinositol-anchored glycoprotein is an evolutionary conserved dual-function receptor and β-NAD+-metabolizing ectoenzyme of the ADP-ribosyl cyclases gene family. Identified as bone marrow stromal cell and myeloid cell differentiation antigen, CD157 turned out to have a wider expression than originally assumed. The functional significance of human CD157 as an enzyme remains unclear, while it was well established in mouse models. Conversely, the receptor role of CD157 has been clearly delineated. In physiological conditions, CD157 is a key player in regulating leukocyte adhesion, migration and diapedesis. Underlying these functional roles is the ability of CD157 to bind with high affinity selected extracellular matrix components within their heparin-binding domains. CD157 binding to extracellular matrix promotes its interaction with β1 and β2-integrins and induces the organization of a multimolecular complex that is instrumental to the delivery of synergistic outside-in signals leading to optimal cell adhesion and migration, both in physiological and in pathological situations. CD157 also regulates cell adhesion and migration and is a marker of adverse prognosis in epithelial ovarian cancer and pleural mesothelioma. This review focuses on human CD157 expression and functions and provides an overview on its role in human pathology and its emerging potential as target for antibody-mediated immunotherapy.

Specific cyclic ADP-ribose phosphohydrolase obtained by mutagenic engineering of Mn2+-dependent ADP-ribose/CDP-alcohol diphosphatase

Cyclic ADP-ribose (cADPR) is a messenger for Ca²⁺ mobilization. Its turnover is believed to occur by glycohydrolysis to ADP-ribose. However, ADP-ribose/CDP-alcohol diphosphatase (ADPRibase-Mn) acts as cADPR phosphohydrolase with much lower efficiency than on its major substrates. Recently, we showed that mutagenesis of human ADPRibase-Mn at Phe³⁷, Leu¹⁹⁶ and Cys²⁵³ alters its specificity: the best substrate of the mutant F37A + L196F + C253A is cADPR by a short difference, Cys²⁵³ mutation being essential for cADPR preference. Its proximity to the 'northern' ribose of cADPR in docking models indicates Cys²⁵³ is a steric constraint for cADPR positioning. Aiming to obtain a specific cADPR phosphohydrolase, new mutations were tested at Asp²⁵⁰, Val²⁵², Cys²⁵³ and Thr²⁷⁹, all near the 'northern' ribose. First, the mutant F37A + L196F + C253G, with a smaller residue 253 (Ala > Gly), showed increased cADPR specificity. Then, the mutant F37A + L196F + V252A + C253G, with another residue made smaller (Val > Ala), displayed the desired specificity, with cADPR k_cat/K_M ≈20-200-fold larger than for any other substrate. When tested in nucleotide mixtures, cADPR was exhausted while others remained unaltered. We suggest that the specific cADPR phosphohydrolase, by cell or organism transgenesis, or the designed mutations, by genome editing, provide opportunities to study the effect of cADPR depletion on the many systems where it intervenes.

Genome-wide DNA methylation at birth in relation to in utero arsenic exposure and the associated health in later life

BACKGROUND

In utero arsenic exposure may alter fetal developmental programming by altering DNA methylation, which may result in a higher risk of disease in later life. We evaluated the association between in utero arsenic exposure and DNA methylation (DNAm) in cord blood and its influence in later life.

METHODS

Genome-wide DNA methylation in cord blood from 64 subjects in the Taiwanese maternal infant and birth cohort was analyzed. Robust regressions were applied to assess the association of DNA methylation with in utero arsenic exposure. Multiple testing was adjusted by controlling false discovery rate (FDR) of 0.05. The DAVID bioinformatics tool was implemented for functional annotation analyses on the detected CpGs. The identified CpGs were further tested in an independent cohort. For the CpGs replicated in the independent cohort, linear mixed models were applied to assess the association of DNA methylation with low-density lipoprotein (LDL) at different ages (2, 5, 8, 11 and 14 years).

RESULTS

In total, 579 out of 385,183 CpGs were identified after adjusting for multiple testing (FDR = 0.05), of which ~60% were positively associated with arsenic exposure. Functional annotation analysis on these CpGs detected 17 KEGG pathways (FDR = 0.05) including pathways for cardiovascular diseases (CVD) and diabetes mellitus. In the independent cohort, about 46% (252 out of 553 CpGs) of the identified CpGs showed associations consistent with those in the study cohort. In total, 11 CpGs replicated in the independent cohort were in the pathways related to CVD and diabetes mellitus. Via longitudinal analyses, we found at 5 out of the 11 CpGs methylation was associated with LDL over time and interactions between DNA methylation and time were observed at 4 of the 5 CpGs, cg25189764 (coeff = 0.157, p-value = 0.047), cg04986899 (coeff. For interaction [coeff.int] = 0.030, p-value = 0.024), cg04903360 (coeff.int = 0.026, p-value = 0.032), cg08198265 (coeff.int = -0.063, p-value = 0.0021), cg10473311 (coeff.int = -0.021, p-value = 0.027).

CONCLUSION

In utero arsenic exposure was associated with cord blood DNA methylation at various CpGs. The identified CpGs may help determine pathological epigenetic mechanisms linked to in utero arsenic exposure. Five CpGs (cg25189764, cg04986899, cg04903360, cg08198265 and cg10473311) may serve as epigenetic markers for changes in LDL later in life.

Functional annotation of rare gene aberration drivers of pancreatic cancer

As we enter the era of precision medicine, characterization of cancer genomes will directly influence therapeutic decisions in the clinic. Here we describe a platform enabling functionalization of rare gene mutations through their high-throughput construction, molecular barcoding and delivery to cancer models for in vivo tumour driver screens. We apply these technologies to identify oncogenic drivers of pancreatic ductal adenocarcinoma (PDAC). This approach reveals oncogenic activity for rare gene aberrations in genes including NAD Kinase (NADK), which regulates NADP(H) homeostasis and cellular redox state. We further validate mutant NADK, whose expression provides gain-of-function enzymatic activity leading to a reduction in cellular reactive oxygen species and tumorigenesis, and show that depletion of wild-type NADK in PDAC cell lines attenuates cancer cell growth in vitro and in vivo. These data indicate that annotating rare aberrations can reveal important cancer signalling pathways representing additional therapeutic targets.

Anxiety- and depression-like behavior in mice lacking the CD157/BST1 gene, a risk factor for Parkinson's disease

CD157, known as bone marrow stromal cell antigen-1, is a glycosylphosphatidylinositol-anchored ADP-ribosyl cyclase that supports the survival and function of B-lymphocytes and hematopoietic or intestinal stem cells. Although CD157/Bst1 is a risk locus in Parkinson's disease (PD), little is known about the function of CD157 in the nervous system and contribution to PD progression. Here, we show that no apparent motor dysfunction was observed in young knockout (CD157 (-/-)) male mice under less aging-related effects on behaviors. CD157 (-/-) mice exhibited anxiety-related and depression-like behaviors compared with wild-type mice. These behaviors were rescued through treatment with anti-psychiatric drugs and oxytocin. CD157 was weakly expressed in the amygdala and c-Fos immunoreactivity in the amygdala was less evident in CD157 (-/-) mice than in wild-type mice. These results demonstrate for the first time that CD157 plays a role as a neuro-regulator and suggest a potential role in pre-motor symptoms in PD.

Cluster of differentiation 38 (CD38) mediates bile acid-induced acinar cell injury and pancreatitis through cyclic ADP-ribose and intracellular calcium release

Aberrant Ca(2+) signals within pancreatic acinar cells are an early and critical feature in acute pancreatitis, yet it is unclear how these signals are generated. An important mediator of the aberrant Ca(2+) signals due to bile acid exposure is the intracellular Ca(2+) channel ryanodine receptor. One putative activator of the ryanodine receptor is the nucleotide second messenger cyclic ADP-ribose (cADPR), which is generated by an ectoenzyme ADP-ribosyl cyclase, CD38. In this study, we examined the role of CD38 and cADPR in acinar cell Ca(2+) signals and acinar injury due to bile acids using pharmacologic inhibitors of CD38 and cADPR as well as mice deficient in Cd38 (Cd38(-/-)). Cytosolic Ca(2+) signals were imaged using live time-lapse confocal microscopy in freshly isolated mouse acinar cells during perifusion with the bile acid taurolithocholic acid 3-sulfate (TLCS; 500 μM). To focus on intracellular Ca(2+) release and to specifically exclude Ca(2+) influx, cells were perifused in Ca(2+)-free medium. Cell injury was assessed by lactate dehydrogenase leakage and propidium iodide uptake. Pretreatment with either nicotinamide (20 mM) or the cADPR antagonist 8-Br-cADPR (30 μM) abrogated TLCS-induced Ca(2+) signals and cell injury. TLCS-induced Ca(2+) release and cell injury were reduced by 30 and 95%, respectively, in Cd38-deficient acinar cells compared with wild-type cells (p < 0.05). Cd38-deficient mice were protected against a model of bile acid infusion pancreatitis. In summary, these data indicate that CD38-cADPR mediates bile acid-induced pancreatitis and acinar cell injury through aberrant intracellular Ca(2+) signaling.

Transforming growth factor-β induces epithelial to mesenchymal transition and suppresses the proliferation and transdifferentiation of cultured human pancreatic duct cells

Pancreatic duct cells are considered a potential source of β-cell regeneration, and transforming growth factor-β (TGF-β) has been suggested to perform an important role in these processes, but the underlying mechanism of the signal pathways, especially in humans, remains poorly understood. To evaluate the role of TGF-β1, pancreatic duct cells were isolated from three brain-dead organ donors. Pancreatic cell clusters harvested after islet isolation were dispersed to single cells and cultured in monolayers, then treated with TGF-β1. We analyzed the characteristics of the cultured cells, the TGF-β1 intracellular signaling pathway, the proliferation, and transdifferentiation rates of the duct cells. We also evaluated the genes and protein expression patterns after TGF-β1 treatment. After TGF-β1 treatment, typical morphologic changes representative of EMT were observed and Erk1/2, JNK, and AKT phosphorylation, Ras downstream effectors, were increased. β cell-specific transcription factors including PDX-1, Beta2/NeuroD, Ist-1, and NGN3 were markedly suppressed and the rate of transdifferentiation into β cells was also suppressed. Genomic and proteomic analyses suggested that TGF-β1 induces marked changes in a variety of structural genes and proteins associated with EMT. In conclusion, TGF-β1 induces EMT in cultured human pancreatic duct cells, but suppresses its proliferation and transdifferentiation into β cells. Our results are the first report of TGF-β1 effects for EMT and ductal cell transdifferentiation and proliferation at the protein level in human pancreatic duct cells.

Stem cell genes are poorly expressed in chondrocytes from microtic cartilage

OBJECTIVES

This study was aimed to see the difference between chondrocytes from normal cartilage compared to chondrocytes from microtic cartilage. Specific attentions were to characterize the growth of chondrocytes in terms of cell morphology, growth profile and RT-PCR analysis.

STUDY DESIGN

Laboratory experiment using auricular chondrocytes.

METHODS

Chondrocytes were isolated from normal and microtic human auricular cartilage after ear reconstructive surgeries carried out at the Universiti Kebangsaan Malaysia Medical Centre. Chondrocytes were cultured in vitro and subcultured until passage 4. Upon confluency, cultured chondrocytes at each passage (P1, P2, P3 and P4) were harvested and subjected to growth profile and gene expression analyses. Comparison was made between the microtic and normal chondrocytes.

RESULTS

For growth profile analysis cell viability did not show significant differences between both samples. There are no significance differences between both samples in terms of its growth rate, except in passage 1 where microtic chondrocytes were significant lower in their growth rate. Population doubling time and total number of cell doubling of all samples also did not show any significant differences. Gene expression is measured using Real Time-Reverse Transcriptase Polymerase Chain Reaction (RT-PCR). There is no significant differences in the expression of collagen type I, collagen type II, collagen type X, aggrecan core protein, elastin and sox9 genes in both samples. There are significant lower in the expression of sox2, nestin, BST-1 and OCT-4 gene in microtic chondrocytes compared to the normal chondrocytes. Stem cells markers are included in this study as stemness in cells may imply a greater proliferative potential and plasticity in vitro.

CONCLUSION

Chondrocytes from microtic samples have the same properties as chondrocytes from normal samples and hold promises to be used as a starting material in the reconstruction of the external ear in future clinical application. The reduction in sox2, nestin, BST-1 and OCT-4 gene expression in microtic samples could be the possible cause of the arrested development of the external ear.

Review: NAD +: a modulator of immune functions

Latterly, nicotinamide adenine dinucleotide (NAD+) has emerged as a molecule with versatile functions and of enormous impact on the maintenance of cell integrity. Besides playing key roles in almost all major aspects of energy metabolism, there is mounting evidence that NAD+ and its degradation products affect various biological activities including calcium homeostasis, gene transcription, DNA repair, and intercellular communication. This review is aimed at giving a brief insight into the life cycle of NAD+ in the cell, referring to synthesis, action and degradation aspects. With respect to their immunological relevance, the importance and function of the major NAD+ metabolizing enzymes, namely CD38/CD157, ADP-ribosyltransferases (ARTs), poly-ADP-ribose-polymerases (PARPs), and sirtuins are summarized and roles of NAD+ and its main degradation product adenosine 5'-diphosphoribose (ADPR) in cell signaling are discussed. In addition, an outline of the variety of immunological processes depending on the activity of nicotinamide phosphoribosyltransferase (Nampt), the key enzyme of the salvage pathway of NAD+ synthesis, is presented. Taken together, an efficient supply of NAD+ seems to be a crucial need for a multitude of cell functions, underlining the yet only partly revealed potency of this small molecule to influence cell fate.

Evolution and function of the ADP ribosyl cyclase/CD38 gene family in physiology and pathology

The membrane proteins CD38 and CD157 belong to an evolutionarily conserved family of enzymes that play crucial roles in human physiology. Expressed in distinct patterns in most tissues, CD38 (and CD157) cleaves NAD(+) and NADP(+), generating cyclic ADP ribose (cADPR), NAADP, and ADPR. These reaction products are essential for the regulation of intracellular Ca(2+), the most ancient and universal cell signaling system. The entire family of enzymes controls complex processes, including egg fertilization, cell activation and proliferation, muscle contraction, hormone secretion, and immune responses. Over the course of evolution, the molecules have developed the ability to interact laterally and frontally with other surface proteins and have acquired receptor-like features. As detailed in this review, the loss of CD38 function is associated with impaired immune responses, metabolic disturbances, and behavioral modifications in mice. CD38 is a powerful disease marker for human leukemias and myelomas, is directly involved in the pathogenesis and outcome of human immunodeficiency virus infection and chronic lymphocytic leukemia, and controls insulin release and the development of diabetes. Here, the data concerning diseases are examined in view of potential clinical applications in diagnosis, prognosis, and therapy. The concluding remarks try to frame all of the currently available information within a unified working model that takes into account both the enzymatic and receptorial functions of the molecules.

CD38 autoimmunity: recent advances and relevance to human diabetes

Human CD38 is a protein which catalyzes the synthesis of nicotinic acid adenine dinucleotide (NAADP+) and the conversion of NAD+ to cADPR. Both cADPR and NAADP+ are powerful intracellular Ca2+ ([Ca2+]i) mobilizers in different cell types. Recently, the presence of CD38 autoantibodies has been found in a significant number (9-15%) of patients with Type 2 or long-standing Type 1 diabetes. These autoantibodies are biologically active, the majority of them (-60%) displaying agonistic properties, i.e., [Ca2+]i mobilization in lymphocytic cell lines and in pancreatic islets. In cultured rat pancreatic islets, the human autoantibodies inhibit glucose-induced insulin release, whereas, in human pancreatic islets CD38 autoantibodies stimulate glucose-mediated insulin secretion. The clinical phenotype of anti-CD38-positive Type 2 diabetes differs from the LADA (latent autoimmune diabetes of adults) phenotype. When accurately matched for age and obesity, only LADA patients with anti-GAD antibodies, but not GAD-negative/ CD38-positive patients, have reduced in vivo beta-cell function in comparison to antibody-negative patients. Transgenic mice overexpressing CD38 show enhanced glucose-induced insulin release, whereas, conversely, CD38 knockout mice display a severe impairment in beta-cell function. Few Japanese diabetic patients carry a missense mutation in the CD38 gene; in Caucasian patients mutations in the CD38 gene have not been found. Collectively, these findings suggest that activation of CD38 represents an alternative signaling pathway for glucose-induced insulin secretion in human beta-cells. More information, however, is necessary to gauge the role of CD38 autoimmunity in the context of the natural history of human Type 1 or Type 2 diabetes.

Evidence for an intracellular ADP-ribosyl cyclase/NAD+-glycohydrolase in brain from CD38-deficient mice

Cyclic ADP-ribose, a metabolite of NAD+, is known to modulate intracellular calcium levels and signaling in various cell types, including neural cells. The enzymes responsible for producing cyclic ADP-ribose in the cytoplasm of mammalian cells remain unknown; however, two mammalian enzymes that are capable of producing cyclic ADP-ribose extracellularly have been identified, CD38 and CD157. The present study investigated whether an ADP-ribosyl cyclase/NAD+-glycohydrolase independent of CD38 is present in brain tissue. To address this question, NAD+ metabolizing activities were accurately examined in developing and adult Cd38-/- mouse brain protein extracts and cells. Low ADP-ribosyl cyclase and NAD+-glycohydrolase activities (in the range of pmol of product formed/mg of protein/min) were detected in Cd38-/- brain at all developmental stages studied. Both activities were found to be associated with cell membranes. The activities were significantly higher in Triton X-100-treated neural cells compared with intact cells, suggesting an intracellular location of the novel cyclase. The cyclase and glycohydrolase activities were optimal at pH 6.0 and were inhibited by zinc, properties which are distinct from those of CD157. Both activities were enhanced by guanosine 5'-O-(3-thiotriphosphate), a result suggesting that the novel enzyme may be regulated by a G protein-dependent mechanism. Altogether our results indicate the presence of an intracellular membrane-bound ADP-ribosyl cyclase/NAD+-glycohydrolase distinct from CD38 and from CD157 in mouse brain. This novel enzyme, which is more active in the developing brain than in the adult tissue, may play an important role in cyclic ADP-ribose-mediated calcium signaling during brain development as well as in adult tissue.

CD157, the Janus of CD38 but with a unique personality

CD157 is a pleiotropic ectoenzyme which belongs to the CD38 family and to the growing number of leukocyte surface molecules known to act independently as both receptors and enzymes. A 45-kDa surface structure with a GPI anchor, the CD157 molecule displays two distinct domains in its extracellular component. The first is implicated in the enzymic activities of the molecule and the second features adhesion/signalling properties. CD157 shares several characteristics with CD38, including a similar amino acid sequence and enzymic functions. Both molecules are involved in the metabolism of NAD(+), and the CD157 gene is synthenic on 4p15 with CD38, with which it also shares a unique genomic organization. Their conservation in phylogeny is striking evidence for their relevance in the life and death cycle of the cell.

Human CD38: a (r)evolutionary story of enzymes and receptors

Human CD38 is the mammalian prototype of a family of proteins which share structural similarities and an ectoenzymatic activity involved in the production of calcium mobilizing compounds. Besides the enzymatic activity, the molecule performs as a receptor, ruling adhesion and signaling in leukocytes. These functions are exerted through the interaction with surface ligands, one of which was identified as CD31. Recently, CD38 has gained attention as a prognostic marker and a pathogenetic agent in leukemias and in other diseases. Together these insights have produced a model of an as yet unique family of molecules, which act independently as receptors and enzymes.

ADP-Ribosyl cyclase in rat salivary glands

Both the Ca(2+)-releasing mechanism induced by cyclic ADP-ribose (cADPR) and the ADP-ribosyl cyclase (ADPRC) activity that converts NAD(+) to cADPR were observed in a variety of cell types. We studied the ADPRC activity in rat major salivary glands that include parotid gland (PG), submandiblar gland (SMG), and sublingual gland (SLG). The enzyme activity responsible for cADPR synthesis was detected by spectrofluorometric assay using NGD(+) as a substrate. The enzyme activities in SLG, SMG, and PG were about 400, 30, and 40 nmol/min/g tissue, respectively, in 5-week-old rats. The highest value was observed in SLG and this value was higher than those in other tissues; e.g., spleen (200 nmol/min/g tissue). The enzyme activity in SLG increased gradually after birth and showed a maximum value at 3 weeks. On the other hand, the enzyme activities almost did not change in both PG and SMG between 0 and 9 weeks. In spite of the high ADPRC activity in SLG, we could not detect the cADPR-induced Ca(2+)-release from SLG microsomes. These results suggest that the ADPRC in SLG does not function through Ca(2+)-release observed in various tissues.

The calcium/calmodulin-dependent phosphodiesterase PDE1C down-regulates glucose-induced insulin secretion

To understand the role cAMP phosphodiesterases (PDEs) play in the regulation of insulin secretion, we analyzed cyclic nucleotide PDEs of a pancreatic beta-cell line and used family and isozyme-specific PDE inhibitors to identify the PDEs that counteract glucose-stimulated insulin secretion. We demonstrate the presence of soluble PDE1C, PDE4A and 4D, a cGMP-specific PDE, and of particulate PDE3, activities in betaTC3 insulinoma cells. Selective inhibition of PDE1C, but not of PDE4, augmented glucose-stimulated insulin secretion in a dose-dependent fashion thus demonstrating that PDE1C is the major PDE counteracting glucose-dependent insulin secretion from betaTC3 cells. In pancreatic islets, inhibition of both PDE1C and PDE3 augmented glucose-dependent insulin secretion. The PDE1C of betaTC3 cells is a novel isozyme possessing a K(m) of 0.47 microM for cAMP and 0.25 microM for cGMP. The PDE1C isozyme of betaTC3 cells is sensitive to 8-methoxymethyl isobutylmethylxanthine and zaprinast (IC(50) = 7.5 and 4.5 microM, respectively) and resistant to vinpocetine (IC(50) > 100 microM). Increased responsiveness of PDE1C activity to calcium/calmodulin is evident upon exposure of cells to glucose. Enhanced cAMP degradation by PDE1C, due to increases in its responsiveness to calcium/calmodulin and in intracellular calcium, constitutes a glucose-dependent feedback mechanism for the control of insulin secretion.

Deletion of Bone Marrow Stromal Cell Antigen-1 (CD157) Gene Impaired Systemic Thymus Independent-2 Antigen-Induced IgG3 and Mucosal TD Antigen-Elicited IgA Responses

Bone marrow stromal cell Ag-1 (BST-1; CD157)-deficient mice were generated to examine the immunologic roles of the molecule in vivo. In BST-1−/− mice, the development of peritoneal B-1 cells was delayed, and CD38low/− B-lineage cells were increased in the bone marrow and spleen. Partial impairment of thymus-independent (TI-2) and thymus-dependent (TD) Ag-specific immune responses was noted in the systemic and mucosal compartments of BST-1−/− mice, respectively. Although serum Ig levels as well as TD and TI-1 Ag-specific systemic immune responses were normal, the TI-2 Ag-induced IgG3 response was selectively impaired. Oral immunization of BST-1−/− mice with cholera toxin, a potent TD Ag for the induction of IgA response, resulted in the poor production of Ag-specific Abs at the intestinal mucosa accompanied by the reduced number of Ag-specific IgA-producing cells in the lamina propria. These results indicate that BST-1 has roles in B cell development and Ab production in vivo.

Nurse-like cells from bone marrow and synovium of patients with rheumatoid arthritis promote survival and enhance function of human B cells

Thymic nurse cells are known to interact with T cells and play a role in their functional maturation. However, the role of nurse cells in B cell maturation and differentiation is less well established, especially at extralymphoid sites. To address this issue, nurse-like cell clones from bone marrow and synovial tissue of patients with RA (RA-NLC) were established and characterized. RA-NLC constitutively expressed CD29, CD49c, CD54 (ICAM-1), CD106 (VCAM-1), CD157 (BST-1), and class I MHC molecules, and secreted IL-6, IL-7, IL-8, granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF). Bone marrow-derived and synovial RA-NLC differed in that the former secreted IL-7 and expressed a greater density of CD157 constitutively and after stimulation with IFNgamma, whereas the latter secreted G-CSF and more IL-6. Stimulation of both bone marrow and synovial RA-NLC induced expression of CD40 and class II MHC, but not CD154 (CD40L) or CD35. RA-NLC rescued peripheral B cells from spontaneous apoptosis and promoted survival of B cells for > 4 wk. B cell survival was blocked by antibodies to CD106 or CD157. RA-NLC also increased Ig production from B cells. After long-term culture (4-6 wk) with RA-NLC, but not alone or with fibroblasts, outgrowth of B cells was observed. All B cell lines derived from these cultures had been transformed by EBV, although the RA-NLC themselves were not infected with EBV. Precursor frequency analysis indicated that approximately 1 in 12,500 peripheral B cells could give rise to these EBV-transformed B cell lines upon coculture with RA-NLC. These results indicate that RA-NLC from bone marrow and synovium have the capacity to rescue B cells from spontaneous apoptosis, facilitate Ig production, and promote the outgrowth of EBV-transformed B lymphoblastoid cells. These findings suggest that RA-NLC may play a role in the local and systemic hyperreactivity of B cells characteristic of rheumatoid arthritis.

Cyclic ADP-ribose and inositol 1,4,5-trisphosphate as alternate second messengers for intracellular Ca2+ mobilization in normal and diabetic beta-cells

Intracellular Ca2+ mobilization occurs in a variety of cellular processes and is mediated by two major systems, the inositol 1,4, 5-trisphosphate (IP3) and cyclic ADP-ribose (cADPR) systems. cADPR has been proposed to be a second messenger for insulin secretion induced by glucose in pancreatic beta-cells (Takasawa, S., Nata, K., Yonekura, H., and Okamoto, H. (1993) Science 259, 370-373). Here we show that the cADPR signal system for insulin secretion is replaced by the IP3 system in diabetic beta-cells such as ob/ob mouse islets and RINm5F cells. We measured the cADPR content in these beta-cells by radioimmunoassay and found that the increase of the cADPR content by glucose did not occur in ob/ob mouse islets and RINm5F cells, whereas the increased cADPR level by glucose was observed in normal rat and mouse islets. Microsomes of these diabetic beta-cells released Ca2+ in response to IP3 but not to cADPR. In the diabetic beta-cells, CD38 (ADP-ribosyl cyclase/cADPR hydrolase) and type 2 ryanodine receptor mRNAs were scarcely detected and, in contrast, an increased expression of IP3 receptor mRNAs was observed. The diabetic beta-cells secreted insulin rather by carbamylcholine than by glucose.

Regulation of glycosylphosphatidylinositol-specific phospholipase D secretion from beta TC3 cells

Glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) is abundant in mammalian serum, but the source of the circulating enzyme is unknown. Pancreatic islets have been reported to contain and secrete GPI-PLD. In this report we examined the regulation of GPI-PLD secretion from beta TC3 cells, a mouse insulinoma cell line. In the absence of glucose, phorbol myristic acid (0.1 microM) stimulated insulin secretion by 2.5-fold and GPI-PLD secretion by 2-fold. Carbachol (5 microM), glucagon-like peptide I-(7-36) amide (0.1 microM), and isobutylmethylxanthine (0.1 mM) had no significant effect on insulin or GPI-PLD secretion in the absence of glucose. Glucose (16.7 mM) stimulated both GPI-PLD and insulin secretion from beta TC3 cells by 55% and 235%, respectively. In addition, glucose potentiated the secretagogue effect of isobutylmethylxanthine, phorbol myristic acid, and glucagon-like peptide I on both insulin and GPI-PLD secretion. By immunohistochemistry and confocal microscopy, beta TC3 cells contain both insulin and GPI-PLD, which generally colocalized intracellularly. However, GPI-PLD secretion differed from insulin secretion by a higher rate of basal release (2.8% vs. 0.23%/h), a lower magnitude of response to secretagogues, and a more prolonged period of increased secretion. These results demonstrate that beta TC3 cells secrete GPI-PLD in response to insulin secretagogues and suggest that GPI-PLD may be secreted via the regulated pathway in these cells.