CD38 is associated with lipid rafts and upon receptor stimulation leads to Akt/protein kinase B and Erk activation in the absence of the CD3-zeta immune receptor tyrosine-based activation motifs

Evolving roles of CD38 metabolism in solid tumour microenvironment

Given that plenty of clinical findings and reviews have already explained in detail on the progression of CD38 in multiple myeloma and haematological system tumours, here we no longer give unnecessary discussion on the above progression. Though therapeutic antibodies have been regarded as a greatest breakthrough in multiple myeloma immunotherapies due to the durable anti-tumour responses in the clinic, but the role of CD38 in the immunologic regulation and evasion of non-hematopoietic solid tumours are just initiated and controversial. Therefore, we will focus on the bio-function of CD38 enzymatic substrates or metabolites in the variety of non-hematopoietic malignancies and the potential therapeutic value of targeting the CD38-NAD+ or CD38-cADPR/ADPR signal axis. Though limited, we review some ongoing researches and clinical trials on therapeutic approaches in solid tumour as well.

The emerging scenario of immunotherapy for T-cell Acute Lymphoblastic Leukemia: advances, challenges and future perspectives

T-cell acute lymphoblastic leukemia (T-ALL) is a challenging pediatric and adult haematologic disease still associated with an unsatisfactory cure rate. Unlike B-ALL, the availability of novel therapeutic options to definitively improve the life expectancy for relapsed/resistant patients is poor. Indeed, the shared expression of surface targets among normal and neoplastic T-cells still limits the efficacy and may induce fratricide effects, hampering the use of innovative immunotherapeutic strategies. However, novel monoclonal antibodies, bispecific T-cell engagers (BTCEs), and chimeric antigen receptors (CAR) T-cells recently showed encouraging results and some of them are in an advanced stage of pre-clinical development or are currently under investigation in clinical trials. Here, we review this exciting scenario focusing on most relevant advances, challenges, and perspectives of the emerging landscape of immunotherapy of T-cell malignancies.

CD38 Correlates with an Immunosuppressive Treg Phenotype in Lupus-Prone Mice

CD38 is a transmembrane glycoprotein expressed by T-cells. It has been reported that patients with systemic lupus erythematosus (SLE) showed increased CD38⁺CD25⁺ T-cells correlating with immune activation and clinical signs. Contrariwise, CD38 deficiency in murine models has shown enhanced autoimmunity development. Recent studies have suggested that CD38⁺ regulatory T-cells are more suppressive than CD38⁻ regulatory T-cells. Thus, we have suggested that CD38 overexpression in SLE patients could play a role in regulating immune activation cells instead of enhancing it. This study found a correlation between CD38 with FoxP3 expression and immunosuppressive molecules (CD69, IL-10, CTLA-4, and PD-1) in T-cells from lupus-prone mice (B6.MRL-Fas^lpr/J). Additionally, B6.MRL-Fas^lpr/J mice showed a decreased proportion of CD38⁺ Treg cells regarding wild-type mice (WT). Furthermore, Regulatory T-Cells (Treg cells) from CD38-/- mice showed impairment in expressing immunosuppressive molecules and proliferation after stimulation through the T-cell receptor (TCR). Finally, we demonstrated an increased ratio of IFN-γ/IL-10 secretion in CD38-/- splenocytes stimulated with anti-CD3 compared with the WT. Altogether, our data suggest that CD38 represents an element in maintaining activated and proliferative Treg cells. Consequently, CD38 could have a crucial role in immune tolerance, preventing SLE development through Treg cells.

Facts and Challenges in Immunotherapy for T-Cell Acute Lymphoblastic Leukemia

T-cell acute lymphoblastic leukemia (T-ALL), a T-cell malignant disease that mainly affects children, is still a medical challenge, especially for refractory patients for whom therapeutic options are scarce. Recent advances in immunotherapy for B-cell malignancies based on increasingly efficacious monoclonal antibodies (mAbs) and chimeric antigen receptors (CARs) have been encouraging for non-responding or relapsing patients suffering from other aggressive cancers like T-ALL. However, secondary life-threatening T-cell immunodeficiency due to shared expression of targeted antigens by healthy and malignant T cells is a main drawback of mAb—or CAR-based immunotherapies for T-ALL and other T-cell malignancies. This review provides a comprehensive update on the different immunotherapeutic strategies that are being currently applied to T-ALL. We highlight recent progress on the identification of new potential targets showing promising preclinical results and discuss current challenges and opportunities for developing novel safe and efficacious immunotherapies for T-ALL.

CD38 in Neurodegeneration and Neuroinflammation

Neurodegenerative diseases are characterized by neuronal degeneration as well as neuroinflammation. While CD38 is strongly expressed in brain cells including neurons, astrocytes as well as microglial cells, the role played by CD38 in neurodegeneration and neuroinflammation remains elusive. Yet, CD38 expression increases as a consequence of aging which is otherwise the primary risk associated with neurodegenerative diseases, and several experimental data demonstrated that CD38 knockout mice are protected from neurodegenerative and neuroinflammatory insults. Moreover, nicotinamide adenine dinucleotide, whose levels are tightly controlled by CD38, is a recognized and potent neuroprotective agent, and NAD supplementation was found to be beneficial against neurodegenerative diseases. The aims of this review are to summarize the physiological role played by CD38 in the brain, present the arguments indicating the involvement of CD38 in neurodegeneration and neuroinflammation, and to discuss these observations in light of CD38 complex biology.

The Good, the Bad and the Unknown of CD38 in the Metabolic Microenvironment and Immune Cell Functionality of Solid Tumors

The regulation of the immune microenvironment within solid tumors has received increasing attention with the development and clinical success of immune checkpoint blockade therapies, such as those that target the PD-1/PD-L1 axis. The metabolic microenvironment within solid tumors has proven to be an important regulator of both the natural suppression of immune cell functionality and the de novo or acquired resistance to immunotherapy. Enzymatic proteins that generate immunosuppressive metabolites like adenosine are thus attractive targets to couple with immunotherapies to improve clinical efficacy. CD38 is one such enzyme. While the role of CD38 in hematological malignancies has been extensively studied, the impact of CD38 expression within solid tumors is largely unknown, though most current data indicate an immunosuppressive role for CD38. However, CD38 is far from a simple enzyme, and there are several remaining questions that require further study. To effectively treat solid tumors, we must learn as much about this multifaceted protein as possible—i.e., which infiltrating immune cell types express CD38 for functional activities, the most effective CD38 inhibitor(s) to employ, and the influence of other similarly functioning enzymes that may also contribute towards an immunosuppressive microenvironment. Gathering knowledge such as this will allow for intelligent targeting of CD38, the reinvigoration of immune functionality and, ultimately, tumor elimination.

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.

The transferrin receptor CD71 regulates type II CD38, revealing tight topological compartmentalization of intracellular cyclic ADP-ribose production

The CD38 molecule (CD38) catalyzes biogenesis of the calcium-mobilizing messenger cyclic ADP-ribose (cADPR). CD38 has dual membrane orientations, and type III CD38, with its catalytic domain facing the cytosol, has low abundance but is efficient in cyclizing cytosolic NAD to produce cADPR. The role of cell surface type II CD38 in cellular cADPR production is unknown. Here we modulated type II CD38 expression and assessed the effects of this modulation on cADPR levels. We developed a photoactivatable cross-linking probe based on a CD38 nanobody, and, combining it with MS analysis, we discovered that cell surface CD38 interacts with CD71. CD71 knockdown increased CD38 levels, and CD38 knockout reciprocally increased CD71, and both could be cocapped and coimmunoprecipitated. We constructed a chimera comprising the N-terminal segment of CD71 and a CD38 nanobody to mimic CD71's ligand property. Overexpression of this chimera induced a dramatically large decrease in CD38 via lysosomes. Remarkably, cellular cADPR levels did not decrease correspondingly. Bafilomycin-mediated blockade of lysosomal degradation greatly elevated active type II CD38 by trapping it in the lysosomes but also did not increase cADPR levels. Retention of type II CD38 in the endoplasmic reticulum (ER) by expressing an ER construct that prevented its transport to the cell surface likewise did not change cADPR levels. These results provide first and direct evidence that cADPR biogenesis occurs in the cytosol and is catalyzed mainly by type III CD38 and that type II CD38, compartmentalized in the ER or lysosomes or on the cell surface, contributes only minimally to cADPR biogenesis.

HIV Disease Progression: Overexpression of the Ectoenzyme CD38 as a Contributory Factor?

Despite abundant evidence associating CD38 overexpression and CD4 T cell depletion in HIV infection, no causal relation has been investigated. To address this issue, a series of mechanisms are proposed, supported by evidence from different fields, by which CD38 overexpression can facilitate CD4 T cell depletion in HIV infection. According to this model, increased catalytic activity of CD38 may reduce CD4 T cells' cytoplasmic nicotin-amide adenine dinucleotide (NAD), leading to a chronic Warburg effect. This will reduce mitochondrial function. Simultaneously, CD38's catalytic products ADPR and cADPR may be transported to the cytoplasm, where they can activate calcium channels and increase cytoplasmic Ca2+ concentrations, further altering mitochondrial integrity. These mechanisms will decrease the viability and regenerative capacity of CD4 T cells. These hypotheses can be tested experimentally, and might reveal novel therapeutic targets. Also see the video abstract here https://youtu.be/k1LTyiTKPKs.

Liver X Receptor Nuclear Receptors Are Transcriptional Regulators of Dendritic Cell Chemotaxis

The liver X receptors (LXRs) are ligand-activated nuclear receptors with established roles in the maintenance of lipid homeostasis in multiple tissues. LXRs exert additional biological functions as negative regulators of inflammation, particularly in macrophages. However, the transcriptional responses controlled by LXRs in other myeloid cells, such as dendritic cells (DCs), are still poorly understood. Here we used gain- and loss-of-function models to characterize the impact of LXR deficiency on DC activation programs. Our results identified an LXR-dependent pathway that is important for DC chemotaxis. LXR-deficient mature DCs are defective in stimulus-induced migration in vitro and in vivo Mechanistically, we show that LXRs facilitate DC chemotactic signaling by regulating the expression of CD38, an ectoenzyme important for leukocyte trafficking. Pharmacological or genetic inactivation of CD38 activity abolished the LXR-dependent induction of DC chemotaxis. Using the low-density lipoprotein receptor-deficient (LDLR^-/-) LDLR^-/- mouse model of atherosclerosis, we also demonstrated that hematopoietic CD38 expression is important for the accumulation of lipid-laden myeloid cells in lesions, suggesting that CD38 is a key factor in leukocyte migration during atherogenesis. Collectively, our results demonstrate that LXRs are required for the efficient emigration of DCs in response to chemotactic signals during inflammation.

The c-Raf modulator RRD-251 enhances nuclear c-Raf/GSK-3/VDR axis signaling and augments 1,25-dihydroxyvitamin D3-induced differentiation of HL-60 myeloblastic leukemia cells

Differentiation therapy is used in cancer treatment. Epidemiologic studies showed that higher vitamin D levels are associated with reduced cancer risks. However, the therapeutic doses needed for differentiation are accompanied by hypercalcemia and intolerable pathological sequelae. In the present work we evaluated if RRD-251, a small-molecule, can enhance vitamin D3-induced differentiation of leukemic cells, in the hope of decreasing the needed vitamin D3-dose.

We demonstrate that RRD-251 enhances vitamin D3-induced differentiation of leukemic cells, the enrichment of the c-Raf kinase in the nucleus, the binding of nuclear c-Raf to GSK-3, increased phosphorylation of GSK-3 ser 21/9 inhibitory sites, and the binding of GSK-3 to VDR, where GSK-3 inhibition is known to enhance transcriptional activation by VDR. Enhancement of D3-induced p-GSK-3 ser 21/9 by RRD-251 was associated with enhanced Akt-GSK-3 binding, Akt being a known GSK-3 inhibitor, and diminished Erk1/2 binding. Diminishing Erk interaction with GSK-3 was associated with enhanced interaction with Vav1, a known driver of myeloid differentiation. This is redolent of an ATRA/c-Raf/GSK-3/RARα axis we previously reported, although the phosphorylation effects to enhance transcriptional activation on RARα vs VDR diverge. Taken together this indicates potential therapeutic significance for a c-Raf/GSK-3/VDR or RARα axis for leukemic myelo-monocytic differentiation.

Probing the requirement for CD38 in retinoic acid-induced HL-60 cell differentiation with a small molecule dimerizer and genetic knockout

CD38 is an ectoenzyme and receptor with key physiological roles. It metabolizes NAD⁺ to adenosine diphosphate ribose (ADPR) and cyclic ADPR, regulating several processes including calcium signalling. CD38 is both a positive and negative prognostic indicator in leukaemia. In all-trans retinoic acid (RA)-induced differentiation of acute promyelocytic leukaemia and HL-60 cells, CD38 is one of the earliest and most prominently upregulated proteins known. CD38 overexpression enhances differentiation, while morpholino- and siRNA-induced knockdown diminishes it. CD38, via Src family kinases and adapters, interacts with a MAPK signalling axis that propels differentiation. Motivated by evidence suggesting the importance of CD38, we sought to determine whether it functions via dimerization. We created a linker based on the suicide substrate arabinosyl-2′-fluoro-2′-deoxy NAD⁺ (F-araNAD⁺), dimeric F-araNAD⁺, to induce homodimerization. CD38 homodimerization did not affect RA-induced differentiation. Probing the importance of CD38 further, we created HL-60 cell lines with CRISPR/Cas9-mediated CD38 truncations. Deletion of its enzymatic domain did not affect differentiation. Apart from increased RA-induced CD11b expression, ablation of all but the first six amino acids of CD38 affected neither RA-induced differentiation nor associated signalling. Although we cannot discount the importance of this peptide, our study indicates that CD38 is not necessary for RA-induced differentiation.

Spleen Tyrosine Kinase Is Involved in the CD38 Signal Transduction Pathway in Chronic Lymphocytic Leukemia

The survival and proliferation of CLL cells depends on microenvironmental contacts in lymphoid organs. CD38 is a cell surface receptor that plays an important role in survival and proliferation signaling in CLL. In this study we demonstrate SYK's direct involvement in the CD38 signaling pathway in primary CLL samples. CD38 stimulation of CLL cells revealed SYK activation. SYK downstream target AKT was subsequently induced and MCL-1 expression was increased. Concomitant inhibition of SYK by the SYK inhibitor R406 resulted in reduced activation of AKT and prevented upregulation of MCL-1. Moreover, short-term CD38 stimulation enhanced BCR-signaling, as indicated by increased ERK phosphorylation. CXCL12-dependent migration was increased after CD38 stimulation. Treating CLL cells with R406 inhibited CD38-mediated migration. In addition, we observed marked downregulation of CD38 expression for CLL cells treated with R406 compared to vehicle control. Finally, we observed a clear correlation between CD38 expression on CLL cells and SYK-inhibitor efficacy. In conclusion, our study provides deeper mechanistic insight into the effect of SYK inhibition in CLL.

Lipoprotein Lipase as a Prognostic Marker in Chronic Lymphocytic Leukemia

The marked clinical heterogeneity of CLL makes early prognosis assessment important. Lipoprotein lipase (LPL) has been shown to confer adverse prognosis in CLL, recent data indicating it might also contribute to CLL cell survival and metabolism. We determined LPL mRNA expression in unselected peripheral blood of 84 CLL patients by RT PCR. Results were correlated with other prognostic markers and outcome. 30/84 (40 %) of cases were LPL positive based on the cutoff established by ROC analysis. In LPL positive patients significantly shorter median survival (136 vs 258 months, p < 0.0001) and time to first treatment intervals (36 vs 144 months, p < 0.002) were documented. LPL values correlated with male gender, higher stages, more treatment requirement, CD38 positivity and unmutated IgVH genes. Among cases with 13q deletion, LPL positivity identified a subcohort with poor outcome (median survival 108 months vs NR, p < 0.0001). In multivariate analysis, cytogenetic aberrations and LPL had significant impact on survival. Our results confirm that LPL is a strong predictor of outcome in CLL, able to improve prognostic accuracy in good risk cytogenetic subgroups. The relationship between its prognostic and functional role in CLL needs to be explored further.

Sphingolipid Microdomains Mediate CD38 Internalization: Topography of the Endocytosis

Plasma membranes of several cell types contain specialized microdomains (or lipid rafts) enriched in sphingolipids, cholesterol, sphingomyelin, and glycosyl-phosphatidylinositol-anchored proteins. These membrane domains are characterized by detergent insolubility at low temperatures and low buoyant density. Human CD38 is the prototype of a gene family encoding surface molecules endowed with multiple functional activities. The endocytosis of the human CD38 molecule has been investigated in normal lymphocytes and in a number of leukemia- and lymphoma-derived cell lines demonstrating that internalization after CD38 ligation is a reproducible event involving only a fraction of the whole amount of the surface molecule. This study reports the results obtained by conventional, confocal, and electron microscopy on the effects induced by the engagement of the molecule with agonistic mAb, reproducing the signals mediated by its natural ligand. The results demonstrate that the endocytosis induced as consequence of CD38 ligation is preceded by a thorough rearrangement of the cell surface with formation of glycosphingolipid- and cholesterol-rich plasma membrane microdomains. These data suggest that specialized raft microdomains might be the plasma membrane structure through which CD38 translocates at intracellular level. The CD38/lipid interactions during the coated pit formation trigger a process that generate membrane curvature, considered as the first step of CD38 endocytosis. Moreover, ultrastructural studies show that early CD38+ endosomes are pleiomorphic and contain cisternal and vesicular regions. Late endosomes exhibit a complex organisation, containing uncoupled CD38-ligand multivesicular- or multilamellar-regions.

CD38 Monoclonal Antibody Therapies for Multiple Myeloma

The goal of this review is to provide historical, recent preclinical, and current clinical summaries of efforts to understand the CD38 molecule and to develop monoclonal antibodies that target it. We focus particularly on efforts involving multiple myeloma, a malignancy of terminally differentiated B cells that remains incurable despite many advances. An era of anti-CD38 monoclonal antibody therapy for myeloma is approaching, one that, we hope, will enable patients to live longer and better lives.

CD38 expression in early B-cell precursors contributes to extracellular signal-regulated kinase-mediated apoptosis

CD38 is a 45,000 molecular weight transmembrane protein that is expressed in immature and mature lymphocytes. However, the expression and function of CD38 during B-cell differentiation in mice is poorly understood. Here, we report that CD38 is expressed from the earliest stages of B-cell development. Pre-pro-B, pro-B, pre-B and immature B cells from murine bone marrow all stained positive for CD38. Interestingly, CD38 expression increases with B-cell maturation. To assess the role of CD38 during B-cell maturation, CD38-deficient mice were analysed. CD38(-/-) mice showed a significant increase in both the frequency of B-lineage cells and the absolute numbers of pre-pro-B cells in bone marrow; however, no other differences were observed at later stages. CD38 cross-linking in Ba/F3 cells promoted apoptosis and marked extracellular signal-regulated kinase (ERK) phosphorylation, and these effects were reduced by treatment with the mitogen-activated protein kinase/ERK kinase inhibitor PD98059, and similar effects were observed in B-cell precursors from bone marrow. These data demonstrate that B-cell precursors in mouse bone marrow express functional CD38 and implicate the early ligation of CD38 in the ERK-associated regulation of the B-lineage differentiation pathway.

Revealing CD38 cellular localization using a cell permeable, mechanism-based fluorescent small-molecule probe

Nicotinamide adenine dinucleotide (NAD) is increasingly recognized as an important signaling molecule that affects numerous biological pathways. Thus, enzymes that metabolize NAD can have important biological functions. One NAD-metabolizing enzyme in mammals is CD38, a type II transmembrane protein that converts NAD primarily to adenosine diphosphate ribose (ADPR) and a small amount of cyclic adenosine diphosphate ribose (cADPR). Localization of CD38 was originally thought to be only on the plasma membrane, but later reports showed either significant or solely, intracellular CD38. With the efficient NAD-hydrolysis activity, the intracellular CD38 may lead to depletion of cellular NAD, thus producing harmful effects. Therefore, the intracellular localization of CD38 needs to be carefully validated. Here, we report the synthesis and application of a cell permeable, fluorescent small molecule (SR101–F-araNMN) that can covalently label enzymatically active CD38 with minimal perturbation of live cells. Using this fluorescent probe, we revealed that CD38 is predominately on the plasma membrane of Raji and retinoic acid (RA)-treated HL-60 cells. Additionally, the probe revealed no CD38 expression in K562 cells, which was previously reported to have solely intracellular CD38. The finding that very little intracellular CD38 exists in these cell lines suggests that the major enzymatic function of CD38 is to hydrolyze extracellular rather than intracellular NAD. The fluorescent activity-based probes that we developed allow the localization of CD38 in different cells to be determined, thus enabling a better understanding of the physiological function.

Phosphorylation of c-Cbl and p85 PI3K driven by all-trans retinoic acid and CD38 depends on Lyn kinase activity

The leukocyte antigen CD38 is expressed after all-trans retinoic acid (ATRA) treatment in HL-60 myelogenous leukemia cells and promotes induced myeloid differentiation when overexpressed. We found that Vav1 and SLP-76 associate with CD38 in two cell lines, and that these proteins complex with Lyn, a Src family kinase (SFK) upregulated by ATRA. SFK inhibitors PP2 and dasatinib, which enhance ATRA-induced differentiation, were used to evaluate the involvement of Lyn kinase activity in CD38-driven signaling. Cells treated with ATRA for 48h followed by one hour of PP2 incubation show SFK/Lyn kinase inhibition. We observed that Lyn inhibition blocked c-Cbl and p85/p55 PI3K phosphorylation driven by the anti-CD38 agonistic mAb IB4 in ATRA-treated HL-60 cells and untreated CD38+ transfectants. In contrast, cells cultured for 48h following concurrent ATRA and PP2 treatment did not show Lyn inhibition, suggesting ATRA regulates the effects on Lyn. 48h of co-treatment preserved CD38-stimulated c-Cbl and p85/p55 PI3K phosphorylation indicating Lyn kinase activity is necessary for these events. In contrast another SFK inhibitor (dasatinib) which blocks Lyn activity with ATRA co-treatment prevented ATRA-induced c-Cbl phosphorylation and crippled p85 PI3K phosphorylation, indicating Lyn kinase activity is important for ATRA-propelled events potentially regulated by CD38. We found that loss of Lyn activity coincided with a decrease in Vav1/Lyn/CD38 and SLP-76/Lyn/CD38 interaction, suggesting these molecules form a complex that regulates CD38 signaling. Lyn inhibition also reduced Lyn and CD38 binding to p85 PI3K, indicating CD38 facilitates a complex responsible for PI3K phosphorylation. Therefore, Lyn kinase activity is important for CD38-associated signaling that may drive ATRA-induced differentiation.

Plasmalogens rescue neuronal cell death through an activation of AKT and ERK survival signaling

Neuronal cells are susceptible to many stresses, which will cause the apoptosis and neurodegenerative diseases. The precise molecular mechanism behind the neuronal protection against these apoptotic stimuli is necessary for drug discovery. In the present study, we have found that plasmalogens (Pls), which are glycerophospholipids containing vinyl ether linkage at sn-1 position, can protect the neuronal cell death upon serum deprivation. Interestingly, caspse-9, but not caspase-8 and caspase-12, was cleaved upon the serum starvation in Neuro-2A cells. Pls treatments effectively reduced the activation of caspase-9. Furthermore, cellular signaling experiments showed that Pls enhanced phosphorylation of the phosphoinositide 3-kinase (PI3K)-dependent serine/threonine-specific protein kinase AKT and extracellular-signal-regulated kinases ERK1/2. PI3K/AKT inhibitor LY294002 and MAPK/ERK kinase (MEK) inhibitor U0126 treatments study clearly indicated that Pls-mediated cell survival was dependent on the activation of these kinases. In addition, Pls also inhibited primary mouse hippocampal neuronal cell death induced by nutrient deprivation, which was associated with the inhibition of caspase-9 and caspase-3 cleavages. It was reported that Pls content decreased in the brain of the Alzheimer’s patients, which indicated that the reduction of Pls content could endanger neurons. The present findings, taken together, suggest that Pls have an anti-apoptotic action in the brain. Further studies on precise mechanisms of Pls-mediated protection against cell death may lead us to establish a novel therapeutic approach to cure neurodegenerative disorders.

The CD19/CD81 complex physically interacts with CD38 but is not required to induce proliferation in mouse B lymphocytes

In B lymphocytes, the cell surface receptor CD38 is involved in apoptosis of immature B cells, proliferation and differentiation of mature B cells. Although CD38 has been establish as a receptor, its signaling has been only partially characterized. As a result of the lack of signaling motifs in the cytoplasmic domain, CD38 must use a co-receptor to induce signaling within the cell. Accordingly, CD38 has been associated with different receptors such as the T-cell receptor/CD3 complex on T cells, CD16 on natural killer cells and MHC class II molecules on monocytes. The CD19/CD81 complex has been proposed as a co-receptor for CD38 in human B lymphocytes, but little or no characterization has been performed in mice. In this study the contribution of the CD19/CD81 complex in murine CD38 signaling was evaluated. Proliferation assays were performed using CD19(-/-) or CD81(-/-) deficient mice; CFSE-labeled B lymphocytes from wild-type mice and CD19(-/-) , CD81(-/-) and CD38(-/-) deficient mice were stimulated with agonistic antibodies against CD38. Immunoprecipitation and immunofluorescence were also performed to detect protein-protein interactions. Our results indicate that the CD19/CD81 complex interacts with CD38 but this interaction is not required to induce proliferation in mouse B lymphocytes, suggesting that other receptors may contribute to the proliferation induced by CD38 in B lymphocytes.

Altered AKT1 and MAPK1 gene expression on peripheral blood mononuclear cells and correlation with T-helper-transcription factors in systemic lupus erythematosus patients

Kinases have been implicated in the immunopathological mechanisms of Systemic Lupus Erythematosus (SLE). v-akt murine-thymoma viral-oncogene-homolog 1 (AKT1) and mitogen-activated-protein-kinase 1 (MAPK1) gene expressions in peripheral mononuclear cells from thirteen SLE patients with inactive or mild disease were evaluated using quantitative real-time reverse-transcription polymerase-chain-reaction and analyzed whether there was any correlation with T-helper (Th) transcription factors (TF) gene expression, cytokines, and S100A8/S100A9-(Calprotectin). Age- and gender-matched thirteen healthy controls were examined. AKT1 and MAPK1 expressions were upregulated in SLE patients and correlated with Th17-(Retinoic acid-related orphan receptor (ROR)-C), T-regulatory-(Treg)-(Transforming Growth Factor Beta (TGFB)-2), and Th2-(interleukin (IL)-5)-related genes. MAPK1 expression correlated with Th1-(IL-12A, T-box TF-(T-bet)), Th2-(GATA binding protein-(GATA)-3), and IL-10 expressions. IL-10 expression was increased and correlated with plasma Tumor Necrosis Factor (TNF)-α and Th0-(IL-2), Th1-(IL-12A, T-bet), GATA3, Treg-(Forkhead/winged-helix transcription factor- (FOXP)-3), and IL-6 expressions. FOXP3 expression, FOXP3/RORC, and FOXP3/GATA3 expression ratios were increased. Plasma IL-1β, IL-12(p70), Interferon-(IFN)-γ, and IL-6 cytokines were augmented. Plasma IL-1β, IL-6, IL-2, IFN-γ, TNF-α, IL-10, and IL-13 correlated with C-reactive protein, respectively. Increased Calprotectin correlated with neutrophils. Conclusion, SLE patients presented a systemic immunoinflammatory activity, augmented AKT1 and MAPK1 expressions, proinflammatory cytokines, and Calprotectin, together with increased expression of Treg-related genes, suggesting a regulatory feedback opposing the inflammatory activity.

Mice deficient in CD38 develop an attenuated form of collagen type II-induced arthritis

CD38, a type II transmembrane glycoprotein expressed in many cells of the immune system, is involved in cell signaling, migration and differentiation. Studies in CD38 deficient mice (CD38 KO mice) indicate that this molecule controls inflammatory immune responses, although its involvement in these responses depends on the disease model analyzed. Here, we explored the role of CD38 in the control of autoimmune responses using chicken collagen type II (col II) immunized C57BL/6-CD38 KO mice as a model of collagen-induced arthritis (CIA). We demonstrate that CD38 KO mice develop an attenuated CIA that is accompanied by a limited joint induction of IL-1β and IL-6 expression, by the lack of induction of IFNγ expression in the joints and by a reduction in the percentages of invariant NKT (iNKT) cells in the spleen. Immunized CD38 KO mice produce high levels of circulating IgG1 and low of IgG2a anti-col II antibodies in association with reduced percentages of Th1 cells in the draining lymph nodes. Altogether, our results show that CD38 participates in the pathogenesis of CIA controlling the number of iNKT cells and promoting Th1 inflammatory responses.

The CD49d/CD29 complex is physically and functionally associated with CD38 in B-cell chronic lymphocytic leukemia cells

CD49d and CD38 are independent negative prognostic markers in chronic lymphocytic leukemia (CLL). Their associated expression marks a disease subset with a highly aggressive clinical course. Here, we demonstrate a constitutive physical association between the CD49d/CD29 integrin complex and CD38 in primary CLL cells and B-cell lines by (i) cocapping, (ii) coimmunoprecipitation and (iii) cell adhesion experiments using CD49d-specific substrates (vascular-cell adhesion molecule-1 or CS-1/H89 fibronectin fragments). The role of CD38 in CD49d-mediated cell adhesion was studied in CD49d(+)CD38(+) and CD49d(+)CD38(-) primary CLL cells, and confirmed using CD38 transfectants of the originally CD49d(+)CD38(-) CLL-derived cell line Mec-1. Results indicate that CD49d(+)CD38(+) cells adhered more efficiently onto CD49d-specific substrates than CD49d(+)CD38(-) cells (P < 0.001). Upon adhesion, CD49d(+)CD38(+) cells underwent distinctive changes in cell shape and morphology, with higher levels of phosphorylated Vav-1 than CD49d(+)CD38(-) cells (P = 0.0006) and a more complex distribution of F-actin to the adhesion sites. Lastly, adherent CD49d(+)CD38(+) cells were more resistant to serum-deprivation-induced (P < 0.001) and spontaneous (P = 0.03) apoptosis than the CD49d(+)CD38(-) counterpart. Altogether, our results point to a direct role for CD38 in enhancing CD49d-mediated adhesion processes in CLL, thus providing an explanation for the negative clinical impact exerted by these molecules when coexpressed in neoplastic cells.

Increased expression and phosphorylation of the two S100A9 isoforms in mononuclear cells from patients with systemic lupus erythematosus: a proteomic signature for circulating low-density granulocytes

Proteins differentially expressed in peripheral blood mononuclear cells (PBMCs) from systemic lupus erythematosus (SLE) patients versus Normal controls were identified by 2-DE and MALDI-MS. Thus, S100A9 expression was significantly increased in SLE PBMCs relative to Normal PBMCs at both mRNA and protein levels. Increased S100A9 levels in SLE PBMCs correlated positively with the abnormal presence of low-density granulocytes (LDGs) detected by flow-cytometry in the mononuclear cell fractions. Another set of proteins that were differentially expressed in SLE PBMCs formed S100A9-independent clusters, suggesting that these differences in protein expression are in fact reflecting changes in the abundance of specific cell types. In SLE PBMCs spots of the two S100A9 isoforms, S100A9-l and S100A9-s, and their phosphorylated counterparts were identified and confirmed to be phosphorylated at Thr(113) by MS/MS analyses. In addition, the phorbol ester PMA alone or in combination with ionomycin induced a stronger increase in threonine phosphorylation of S100A9 in SLE than in Normal PBMCs, while the same stimuli caused the opposite effect on phosphorylation and activation of Erk1/2, suggesting the existence of an abnormal S100A9 signaling in SLE PBMCs. Therefore, the expansion and activation of LDGs in SLE seems to underlie this prominent S100A9 signature.

CD38 through the life of a murine B lymphocyte

CD38 is a 45 kDa transmembrane receptor expressed in B lymphocytes and other cells from the immune system. It is involved in apoptosis, cell activation, differentiation, and proliferation. CD38 has been used extensively to classify various subpopulations of lymphocytes in both humans and mice. It has also been used as a marker of poor prognosis in some lymphoid pathologies. However, CD38 is not a marker but rather an ectoenzyme and a receptor, where it performs several functions. The CD38 signaling pathway has only been partially studied in various cells of the immune system, where apparently the signaling is different depending on the lineage and differentiation state of the cell, leading to distinct outcomes. In this review, we provide an overview of well-established roles of CD38 signaling B lymphocytes from mice. We also discuss areas that need further clarification to get a broader image of how CD38 performs different functions in B cells and to understand its role in B lymphocyte biology under normal versus pathological conditions.

The role of neurofibromin in N-Ras mediated AP-1 regulation in malignant peripheral nerve sheath tumors

Plexiform neurofibromas commonly found in patients with Neurofibromatosis type I (NF1) have a 5% risk of being transformed into malignant peripheral nerve sheath tumors (MPNST). Germline mutations in the NF1 gene coding for neurofibromin, which is a Ras GTPase activating protein (RasGAP) and a negative regulator of Ras, result in an upregulation of the Ras pathway. We established a direct connection between neurofibromin deficiency and downstream effectors of Ras in cell lines from MPNST patients by demonstrating that knockdown of NF1 expression using siRNA in a NF1 wild type MPNST cell line, STS-26T, activates the Ras/ERK1,2 pathway and increases AP-1 binding and activity. We believe this is the first time the transactivation of AP-1 has been linked directly to neurofibromin deficiency in a disease relevant MPNST cell line. Previously, we have shown that N-Ras is constitutively activated in cell lines derived from independent MPNSTs from NF1 patients. We therefore sought to analyze the role of the N-Ras pathway in deregulating AP-1 transcriptional activity. We show that STS-26T clones conditionally expressing oncogenic N-Ras show increased phosphorylated ERK1,2 and phosphorylated JNK expression concomitant with increased AP-1 activity. MAP kinase pathways (ERK1,2 and JNK) were further examined in ST88-14, a neurofibromin-deficient MPNST cell line. The basal activity of ERK1,2 but not JNK was found to increase AP-1 activity. These experiments further confirmed the link between the loss of neurofibromin and increased activity of Ras/MAP kinase pathways and the activation of downstream transcriptional mechanisms in MPNSTs from NF1 patients.

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.

Acute insulin signaling in pancreatic beta-cells is mediated by multiple Raf-1 dependent pathways

Insulin enhances the proliferation and survival of pancreatic beta-cells, but its mechanisms remain unclear. We hypothesized that Raf-1, a kinase upstream of both ERK and Bad, might be a critical target of insulin in beta-cells. To test this hypothesis, we treated human and mouse islets as well as MIN6 beta-cells with multiple insulin concentrations and examined putative downstream targets using immunoblotting, immunoprecipitation, quantitative fluorescent imaging, and cell death assays. Low doses of insulin rapidly activated Raf-1 by dephosphorylating serine 259 and phosphorylating serine 338 in human islets, mouse islets, and MIN6 cells. The phosphorylation of ERK by insulin was eliminated by exposure to a Raf inhibitor (GW5074) or transfection with a dominant-negative Raf-1 mutant. Insulin also enhanced the interaction between mitochondrial Raf-1 and Bcl-2 agonist of cell death (Bad), promoting Bad inactivation via its phosphorylation on serine 112. Insulin-stimulated ERK phosphorylation was abrogated by calcium chelation, calcineurin and calmodulin-dependent protein kinase II inhibitors, and Ned-19, a nicotinic acid adenine dinucleotide phosphate receptor (NAADPR) antagonist. Blocking Raf-1 and Ca(2+) signaling resulted in nonadditive beta-cell death. Autocrine insulin signaling partly accounted for the effects of glucose on ERK phosphorylation. Our results demonstrate that Raf-1 is a critical target of insulin in primary beta-cells. Activation of Raf-1 leads to both an ERK-dependent pathway that involves nicotinic acid adenine dinucleotide phosphate-sensitive Ca(2+) stores and Ca(2+)-dependent phosphorylation events, and an ERK-independent pathway that involves Bad inactivation at the mitochondria. Together our findings identify a novel insulin signaling pathway in beta-cells and shed light on insulin's antiapoptotic and mitogenic mechanisms.

The immunological synapse, TCR microclusters, and T cell activation

T cell activation begins with the interaction between an antigen-specific T cell and an antigen-presenting cell (APC). This interaction results in the formation of the immunological synapse, which had been considered to be responsible for antigen recognition and T cell activation. Recent advances in imaging analysis have provided new insights into T cell activation. The T cell receptor (TCR) microclusters, TCRs, kinases, and adaptors are generated upon antigen recognition at the interfaces between the T cells and the APCs and serve as a fundamental signaling unit for T cell activation. CD28-mediated costimulation is also found to be regulated by the formation of microclusters. Therefore, the dynamic regulations of TCR and CD28 microcluster formation, migration, and interaction are the key events for the initiation of T cell-mediated immune responses. Comprehensive analyses of the composition and characteristics of the TCR microcluster have identified its dynamic features. This review will outline new discoveries of the microclusters and its related concept in T cell activation.

c-Cbl tyrosine kinase-binding domain mutant G306E abolishes the interaction of c-Cbl with CD38 and fails to promote retinoic acid-induced cell differentiation and G0 arrest

Retinoic acid (RA) causes HL-60 human myeloblastic leukemia cell myeloid differentiation that is dependent on MAPK signaling. The process is propelled by c-Cbl, which binds the CD38 receptor as part of a signaling complex generating MAPK signaling. Here we report that the capability of c-Cbl to do this is lost in the G306E tyrosine kinase-binding domain mutant. Unlike wild-type (WT) c-Cbl, the G306E mutant c-Cbl fails to propel RA-induced differentiation, and disrupts the normal association with CD38. The G306E mutant does, like WT c-Cbl, co-immunoprecipitate with Vav, Slp-76, and p38. But unlike WT c-Cbl, does not cause MAPK signaling. In contrast, the C381A Ring finger domain mutant functions like WT c-Cbl. It binds CD38 and is part of the same apparent c-Cbl/Slp-76/Vav/p38 signaling complex. The C381A mutant causes MAPK signaling and propels RA-induced differentiation. In addition to HL-60 cells and their WT or mutant c-Cbl stable transfectants, the c-Cbl/Vav/Slp-76 complex is also found in NB4 cells where c-Cbl was previously also found to bind CD38. The data are consistent with a model in which the G306E mutant c-Cbl forms a signaling complex that includes Slp-76, Vav, and p38; but does not drive MAPK signaling because it fails to bind the CD38 receptor. Without the G306E mutation the c-Cbl unites CD38 with the signaling complex and delivers a MAPK signal that drives RA-induced differentiation. The results demonstrate the importance of the Gly306 residue in the ability of c-Cbl to propel RA-induced differentiation.

Mechanism-based small molecule probes for labeling CD38 on live cells

CD38 is a type II transmembrane glycoprotein with multiple functions. It acts as an ecto-enzyme as well as a receptor. The enzymatic activity catalyzes the formation of two potent Ca(2+) releasing agents: cyclic adenosine diphosphate ribose (cADPR) from nicotinamide adenine dinucleotide (NAD) and nicotinic acid adenine dinucleotide phosphate (NAADP) from NAD phosphate (NADP). The receptor function of CD38 leads to the phosphorylation of intracellular signaling proteins and the up-regulation of cytokine production in immune cells. These two functions of CD38 underlie its involvement in various biological processes, such as hormone secretion, immune cell differentiation, and immune responses. Clinically, CD38 is used as a negative prognosis marker for chronic lymphatic leukemia (CLL). However, a clear molecular understanding of CD38's role in physiology and pathology is still lacking. To facilitate the study of CD38 at cellular and molecular levels, here we report a mechanism-based method for fluorescently labeling CD38 on live cells. This labeling method does not interfere with the receptor function of CD38 and the downstream signaling. The labeling method is thus a useful tool to study the receptor function of CD38 in live cells. In addition, since the mechanism-based labeling also inhibits the enzymatic activity of CD38, it should be useful for dissecting the receptor function of CD38 without interference from its enzyme function in complicated biological processes.

Evaluation of the antiretroviral effects of a PEG-conjugated peptide derived from human CD38

OBJECTIVE

Cell infection by HIV-1 is inhibited by both the expression of CD38 and a soluble peptide (sCD38p) corresponding to its extracellular membrane-proximal amino acid sequence (amino acids 51 - 74). We show here the effects of PEG conjugation to sCD38p and provide new insights into the mechanisms behind the anti-HIV-1 effects of CD38 and derived peptides.

RESEARCH DESIGN/METHODS

In-vitro and in-silico study.

RESULTS

PEGylation of sCD38p increased its ability to inhibit replication of HIV-1 in MT-4 cells and syncytia formation in cocultures of MT-2 and persistently HIV-1(IIIB)-infected H9(IIIB) cells. In silico modeling suggests that sCD38p and CD4 form stable heterodimers involving, among others, an interaction between lysine 57 (K57) of CD38 and a groove in the CD4 receptor, which, in CD4/gp120 complexes, is partially occupied by a lysine residue of the HIV-1 envelope glycoprotein. K57 substitution with a glycine in sCD38p impaired its ability to inhibit syncytia formation in MT-2/H9(IIIB) cell cocultures and gp120 binding to CD4 in a mouse T cell line expressing human but not mouse CD4.

CONCLUSIONS

PEGylation significantly improves the anti-HIV-1 activity of sCD38p, whose effect is probably due to competition with gp120 for a common binding site on CD4 although other mechanisms cannot be excluded so far. The inhibitory concentrations of the sCD38p-PEG as well as its poor toxicity, merit further consideration in anti-HIV-1 strategies.

Nicotinamide cooperates with retinoic acid and 1,25-dihydroxyvitamin D(3) to regulate cell differentiation and cell cycle arrest of human myeloblastic leukemia cells

Nicotinamide, the amide derivative of vitamin B(3), cooperates with retinoic acid (RA), a form of vitamin A, and 1,25-dihydroxyvitamin D(3) (D3), to regulate cell differentiation and proliferation of human myeloblastic leukemia cells. In human myeloblastic leukemia cells, RA or D3 are known to cause MAPK signaling leading to myeloid or monocytic differentiation and G0 cell cycle arrest. In this process, RA or D3 induces the early expression of CD38, a receptor that causes ERK signaling and propels further differentiation. Our study demonstrates that nicotinamide in combination with RA or D3 affected induced expression levels of CD38, CD11b and CD14, suggesting a cooperative function of nicotinamide and RA or D3. Nicotinamide transiently retarded the initial RA- or D3-induced expression of CD38, which subsequently reached the same nearly 100% expression. Nicotinamide induced ERK activation and further enhanced the RA-induced ERK activation, but the D3-induced ERK activation was diminished by nicotinamide, although levels still exceeded those induced by RA, suggesting lineage-specific nicotinamide responses. Nicotinamide enhanced both RA- and D3-induced CD11b expression, inducible oxidative metabolism, and G0 cell cycle arrest, accelerating their induced occurrence in all instances. Consistent with this, the RA- or D3-induced downregulation of PARP was enhanced by nicotinamide. Nicotinamide thus regulated RA- or D3-induced differentiation and G0 arrest, causing a transient delay in certain early aspects of the progression to terminal differentiation but ultimately accelerating the occurrence of terminally, functionally differentiated G0 cells.

c-Cbl interacts with CD38 and promotes retinoic acid-induced differentiation and G0 arrest of human myeloblastic leukemia cells

Retinoic acid (RA) is known to regulate cell growth and differentiation. In HL-60 human myeloblastic leukemia cells, it causes mitogen-activated protein kinase (MAPK) signaling leading to myeloid differentiation and G(0) cell cycle arrest. This communication reports that expression of the Cbl adaptor caused enhanced extracellular signal-regulated kinase 2 activation and promoted RA-induced differentiation and G(0)-arrest. Stable transfectants ectopically expressing c-Cbl underwent myeloid differentiation faster than wild-type (wt) cells when treated with RA. In contrast, c-Cbl knockdown stable transfectants differentiated slower than wt cells when treated with RA. Cells ectopically expressing c-Cbl had enhanced CD38 expression when treated with RA, and cells ectopically expressing CD38 had enhanced c-Cbl expression, even without with RA, suggesting an interaction between c-Cbl and CD38. Fluorescence resource energy transfer and coimmunoprecipitation showed that c-Cbl and CD38 bind each other. RA causes the gradual down-regulation and eventual loss of c-Cbl expression, resulting in loss of the Cbl-CD38 interaction, suggesting that c-Cbl plays a relatively early role in promoting RA-induced differentiation. RA-induced differentiation can thus be propelled by c-Cbl and by CD38, both of which bind together, enhance the expression of each other, and cause MAPK signaling. There thus seems to be a cooperative role for c-Cbl and CD38, reflected in their direct binding, in propulsion of RA-induced differentiation.

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.

Formation and function of ceramide-enriched membrane platforms with CD38 during M1-receptor stimulation in bovine coronary arterial myocytes

CD38 contains an ADP ribosylcyclase domain that mediates intracellular Ca(2+) signaling by the production of cyclic ADP-ribose (cADPR), but the mechanisms by which the agonists activate this enzyme remain unclear. The present study tested a hypothesis that a special lipid-raft (LR) form, ceramide-enriched lipid platform, contributes to CD38 activation to produce cADPR in response to muscarinic type 1 (M(1)) receptor stimulation in bovine coronary arterial myocytes (CAMs). By confocal microscopic analysis, oxotremorine (Oxo), an M(1) receptor agonist, was found to increase LR clustering on the membrane with the formation of a complex of CD38 and LR components such as GM(1), acid sphingomyelinase (ASMase), and ceramide, a typical ceramide-enriched macrodomain. At 80 microM, Oxo increased LR clustering by 78.8%, which was abolished by LR disruptors, methyl-beta-cyclodextrin (MCD), or filipin. With the use of a fluorescence resonance energy transfer (FRET) technique, 15.5+/-1.9% energy transfer rate (vs. 5.3+/-0.9% of control) between CD38 and LR component, ganglioside M(1) was detected, further confirming the proximity of both molecules. In the presence of MCD or filipin, there were no FRET signals detected. In floated detergent-resistant membrane fractions, CD38 significantly increased in LR fractions of CAMs treated by Oxo. Moreover, MCD or filipin attenuated Oxo-induced production of cADPR via CD38. Functionally, Oxo-induced intracellular Ca(2+) release and coronary artery constriction via cADPR were also blocked by LR disruption or ASMase inhibition. These results provide the first evidence that the formation of ceramide-enriched lipid macrodomains is crucial for Oxo-induced activation of CD38 to produce cADPR in CAMs, and these lipid macrodomains mediate transmembrane signaling of M(1) receptor activation to produce second messenger cADPR.

NAADP-induced Ca(2+ signaling in response to endothelin is via the receptor subtype B and requires the integrity of lipid rafts/caveolae

We have investigated the role of NAADP-mediated Ca(2+) mobilization in endothelin (ET) signaling via endothelin receptor subtype A (ETA) and endothelin receptor subtype B (ETB) in rat peritubular smooth muscle cells. Microinjection and extracellular application of NAADP were both able to elicit Ca(2+) release which was blocked by inhibitory concentrations of NAADP, by impairing Ca(2+) uptake in acidic stores with bafilomycin, and by thapsigargin. Ca(2+) release in response to selective ETB stimulation was abolished by inhibition of NAADP signaling through the same strategies, while these treatments only partially impaired ETA-dependent Ca(2+) signaling, showing that transduction of the ETB signal is dependent on NAADP. In addition, we show that lipid rafts/caveolae contain ETA, ETB, and NAADP/cADPR generating enzyme CD38 and that stimulation of ETB receptors results in increased CD38 activity; interestingly, ETB- (but not ETA-) mediated Ca(2+) responses were antagonized by disruption of lipid rafts/caveolae with methyl-beta-cyclodextrin. These data demonstrate a primary role of NAADP in ETB-mediated Ca(2+) signaling and strongly suggest a novel role of lipid rafts/caveolae in triggering ET-induced NAADP signaling.

Influence of cancer-related gene polymorphisms on clinicopathological features in colorectal cancer

BACKGROUND AND AIM

Single nucleotide polymorphisms (SNP) are shown to be related with cancer incidence. It has been reported that CCND1, p21(cip1)DCC, MTHFR, and EXO1 are related with the risk of malignant neoplasm, but few studies have mentioned the prognosis of the patients. We investigated the SNP of patients and related this to clinicopathological features, including survival rate.

METHOD

DNA from the tissues of primary colorectal cancer was obtained from surgical resections of 114 patients (68 males and 46 females, 29-83 years). The CCND1 polymorphism was analyzed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and those of other genes were investigated by the TaqMan method. The polymorphisms obtained were statistically analyzed for the relationship with clinicopathological features.

RESULTS

The CG + GG allele was more invasive than the CC allele in histological tumor depth in the DCC codon 201 (P = 0.0086). The 677TT allele in MTHFR had a larger tumor size than the 677CC allele (P = 0.028). In EXO1 P757L polymorphism, patients with the TT allele had a statistically reduced survival rate compared with the other alleles. In CCND1 polymorphisms, we found no statistical significance in clinicopathological features.

CONCLUSIONS

From these preliminary data, these polymorphisms would be candidates predicting the clinicopathological features of colorectal cancer, but further more systematic gene analyses are warranted.

Highly purified CD38 sub-populations show no evidence of preferential clonal evolution despite having increased proliferative activity when compared with CD38 sub-populations derived from the same chronic lymphocytic leukaemia patient

In agreement with a recently published manuscript, this present study demonstrated that CD38+ sub-populations had increased proliferative activity as evidenced by higher Ki-67 expression (P < 0.0001). This raised the possibility that the CD38+ fraction is exposed to an increased risk of clonal evolution. However, serial fluorescence in situ hybridisation analysis of highly purified CD38+ and CD38- sub-populations from individual patients revealed no distinct cytogenetic lesions or evidence of preferential clonal evolution in the CD38+ fractions when compared with their CD38- counter-parts (P = 0.13). Furthermore, telomere length analysis revealed that all of the sub-populations had similarly short telomeres (P = 0.31) and comparably low telomerase (TERT) expression (P = 0.75) and telomerase activity (P = 0.88). Subsequent examination of cell-sorted CD38+ and CD38- sub-populations from paired peripheral blood and bone marrow samples taken on the same day showed no significant difference in CD38, Ki-67, TERT expression or telomere lengths, indicating that these chronic lymphocytic leukaemia cells were derived from a single pool trafficking between these two compartments. Taken together, our data show that chronic lymphocytic leukaemia cells derived from bimodal patients all have extensive proliferative histories and have undergone a similar number of cell divisions that is mirrored by the episodic expression of CD38.

Antigen-induced clustering of surface CD38 and recruitment of intracellular CD38 to the immunologic synapse

During immunologic synapse (IS) formation, human CD38 redistributes to the contact area of T cell-antigen-presenting cell (APC) conjugates in an antigen-dependent manner. Confocal microscopy showed that CD38 preferentially accumulated along the contact zone, whereas CD3-zeta redistributed toward the central zone of the IS. APC conjugates with human T cells or B cells transiently expressing CD38-green fluorescent protein revealed the presence of 2 distinct pools of CD38, one localized at the cell membrane and the other in recycling endosomes. Both pools were recruited to the T/APC contact sites and required antigen-pulsed APCs. The process appeared more efficient in T cells than in APCs. CD38 was actively recruited at the IS of T cells by means of Lck-mediated signals. Overexpression of CD38 in T cells increased the levels of antigen-induced intracellular calcium release. Opposite results were obtained by down-regulating surface CD38 expression by means of CD38 siRNA. CD38 blockade in influenza HA-specific T cells inhibited IL-2 and IFN-gamma production, PKC phosphorylation at Thr538, and PKC recruitment to the IS induced by antigen-pulsed APCs. These results reveal a new role for CD38 in modulating antigen-mediated T-cell responses during IS formation.

Alteration of enzymatic properties of cell-surface antigen CD38 by agonistic anti-CD38 antibodies that prolong B cell survival and induce activation

Leukocyte cell-surface antigen CD38 is a single-transmembrane protein. CD38 ligation by anti-CD38 antibodies triggers the growth or apoptosis of immune cells. Although the extracellular domain of CD38 has multifunctional catalytic activities including NAD(+) glycohydrolase and cyclase, the CD38-mediated cell survival or death appears to be independent of its catalytic activity. It is proposed that a conformational change of CD38 triggers the signalling. The conformational change of CD38 could influence its catalytic activity. However, the agonistic anti-CD38 antibody that alters the catalytic activity of CD38 has not been reported so far. In the present study, we demonstrated that two agonistic anti-mouse CD38 mAbs (CS/2 and clone 90) change the catalytic activities of CD38. CS/2 was clearly more potent than clone 90 in prolonging B cell survival and activation. CS/2 inhibited the NAD(+) glycohydrolase activity of both the isolated extracellular domain of CD38 (FLAG-CD38) and cell-surface CD38. Kinetic analysis suggested a non-competitive inhibition. On the other hand, clone 90 stimulated the NAD(+) glycohydrolase activity of FLAG-CD38 and had little effect on the NAD(+) glycohydrolase activity of cell-surface CD38. CS/2 and clone 90 had no effect on the cyclase activity of FLAG-CD38 and inhibited the cyclase activity of cell-surface CD38. Accordingly, these agonistic antibodies probably induce the conformational changes of CD38 that are evident in the distinct alterations of the catalytic site. The antibodies will be useful tools to analyze the conformational change of CD38 in the process of triggering B cell survival and the activation signal.

The Role of Platelet/Endothelial Cell Adhesion Molecule–1 (CD31) and CD38 Antigens in Marrow Microenvironmental Retention of Acute Myelogenous Leukemia Cells

In acute myelogenous leukemia (AML), leukemic cell-microenvironment interactions within various niches (stromal/osteoblastic or sinusoidal endothelial cell niches) have a role in leukemia cell survival and drug resistance. The AML leukemic cells express platelet/endothelial cell adhesion molecule-1 (CD31) and CD38, two adhesion molecules that could interact with microenvironmental elements, i.e., CD31 on the surface of marrow endothelial cells (CD31/CD31 and CD38/CD31 interactions) and hyaluronate (CD38/hyaluronate interactions). We report a physical association of these two antigens on the plasma membrane of myeloid leukemic cells. In this context, in vitro experiments done using interaction-blocking anti-CD31 and anti-CD38 monoclonal antibodies (CLB-HEC75 and OKT10, respectively) indicate that an excess of CD31 on the cell membrane of leukemic cells (CD31/CD38 MFI ratio >1) promotes a homotypic interaction with marrow endothelial cells, resulting in higher transendothelial migration. Conversely, an excess of CD38 (CD31/CD38 MFI ratio <1) allows leukemic cells to be entrapped within the bone marrow microenvironment through hyaluronate adhesion. The results obtained in vitro using fluorescence resonance energy transfer, co-capping, and co-immunoprecipitation experiments, and hyaluronate adhesion and transendothelial migration assays, are supported by immunophenotypic characterization of marrow leukemic cells from 78 AML patients on which CD38 expression levels were found to be positively correlated with those of CD31. Importantly, the excess of CD31 in those samples was associated with a higher peripheral WBC count. These findings indicate that bone marrow retention of AML cells depends on CD31 and CD38 coexpression levels.

Signaling properties of CD38 in the mouse immune system: enzyme-dependent and -independent roles in immunity

The 5th international CD38 meeting, held in Torino, Italy, spanned a range of topics from the role of CD38 as a signaling receptor in lymphocytic tumors to the importance of CD38-derived metabolites in NAD(+) metabolism, calcium signaling, and immune function. This meeting was particularly exciting as data were presented demonstrating that collaborative experiments between enzymologists, biochemists, cell biologists, immunologists, and clinicians have started to unravel the secrets of CD38 biology. It is now clear that all of the products of the CD38 enzyme reaction regulate calcium signal transduction in cell types as diverse as sea urchin oocytes and mammalian lymphocytes. It is also apparent that CD38 plays important immunomodulatory role(s), however there is still much debate on how CD38 mediates its immunoregulatory functions and whether the enzymatic products generated by CD38 are important for immunity. The data presented at this meeting have begun to resolve some of these controversies. First, CD38 regulates the function of leukocytes by enzyme-dependent and enzyme-independent mechanisms. Second, CD38 regulates inflammatory responses by modulating the activity of the responding leukocytes and by altering the activity of non-hematopoietic cells in the inflamed tissue. Finally, crosstalk between CD38 and other NAD(+) utilizing enzymes such as ART2, SIRT1, and PARP-1 impacts NAD(+) homeostasis, inflammation, and immunity. Thus, immunity is regulated by CD38 in multiple and unexpected ways and the new research challenge will be to determine whether we can exploit the complex biology of CD38 to therapeutically regulate the immune system.

CD38 and CD157 as receptors of the immune system: a bridge between innate and adaptive immunity

This paper reviews some of the results and the speculations presented at the Torino CD38 Meeting in June, 2006 and focused on CD38 and CD157 seen as a family of molecules acting as surface receptors of immune cells. This partisan view was adopted in the attempt to combine the enzymatic functions with what the immunologists consider key functions in different cell models. At the moment, it is unclear whether the two functions are correlated, indifferent, or independent. Here we present conclusions inferred exclusively on human cell models, namely T and B lymphocytes, dendritic cells, and granulocytes. As an extra analytical tool, we try to follow in the history of life when the enzymatic and receptorial functions were generated, mixing ontogeny, membrane localization, and cell anchorage.