PubMed Health⌕ Search

Biomedical subjects

Richard J Bram

Publications and source records attributed to Richard J Bram.

13 recordsLinked to original sources
PubMed2006

Renal upregulation of HO-1 reduces albumin-driven MCP-1 production: implications for chronic kidney disease.

Proteinuria contributes to chronic kidney disease by stimulating renal tubular epithelial cells to produce cytokines such as monocyte chemoattractant protein-1 (MCP-1). The present study determined whether cellular overexpression of heme oxygenase-1 (HO-1) can influence albumin-stimulated MCP-1 production. In response to bovine serum albumin, NRK-52E cells constitutively overexpressing HO-1 (HO-1 OE cells) exhibit less induction of MCP-1 mRNA and less production of MCP-1 protein compared with similarly treated, control NRK-52E cells (CON cells). In wild-type NRK-52E cells, and under these conditions, we demonstrate that the induction of MCP-1 is critically dependent on intact NF-kappaB binding sites in the MCP-1 promoter. In response to albumin, CON cells exhibit activation of NF-kappaB, and this is reduced in HO-1 OE cells. Albumin also activates ERK1/2 and increases ERK activity, both of which are exaggerated in HO-1 OE cells. Studies with an inhibitor of MAPK/ERK kinase (U0126) demonstrate that the inhibitory effects of U0126 on MCP-1 production are attenuated in HO-1 OE cells. We conclude that HO-1 overexpression in the proximal tubule reduces MCP-1 production in response to albumin, and this occurs, at least in part, by inhibiting an ERK-dependent, NF-kappaB-dependent pathway at a site that is distal to the activation of ERK. These findings suggest that the induction of HO-1 in the proximal tubule, as occurs in chronic kidney disease, may be a countervailing response that reduces albumin-stimulated production of cytokines such as MCP-1.

Animals↗
PubMed2005

Selective activation of TACI by syndecan-2.

B-lymphocyte homeostasis and function are regulated by complementary actions of the TNFR family members TACI, BCMA, and BAFF-R, which are expressed by mature B cells. How these receptors are differentially activated is not entirely understood, because the primary ligand BAFF binds to all three. We searched for alternative ligands for TACI using recombinant TACI-Fc fusion protein as a probe and identified syndecan-2 as a new binding partner. TACI binding appears to require heparan sulfate posttranslational modifications of syndecan-2, because free heparin or pretreatment with heparitinase blocked the interaction. Syndecan-2 bound TACI but bound neither BAFF-R nor BCMA. Transfected cells expressing syndecan-2 activated signaling through TACI, as indicated by an NFAT-specific reporter. Syndecan-1 and syndecan-4 were also able to induce TACI signaling in a similar manner. This is the first identification of ligands that selectively activate TACI without simultaneously triggering BCMA or BAFF-R. This finding may help explain the alternative outcomes of signaling from this family of receptors in B cells.

B-Cell Activation Factor Receptor↗
PubMed2005

BLyS and APRIL in rheumatoid arthritis.

The cytokines B lymphocyte stimulator (BLyS) and a proliferation-inducing ligand (APRIL) enhance autoimmune disease by sustaining B cell activation. In RA, B cells contribute to the formation of 3 functionally distinct types of lymphoid microarchitectures in the inflamed synovium: ectopic GCs; T cell-B cell aggregates lacking GC reactions; and unorganized, diffuse infiltrates. We examined 72 tissues representing the 3 types of synovitis for BLyS and APRIL production and for expression of APRIL/BLyS receptors. Biologic effects of BLyS and APRIL were explored by treating human synovium-SCID mouse chimeras with the APRIL and BLyS decoy receptor transmembrane activator and CAML interactor:Fc (TACI:Fc). GC+ synovitis had the highest levels of APRIL, produced exclusively by CD83+ DCs. BLyS was present in similar levels in all tissue types and derived exclusively from CD68+ macrophages. In GC+ synovitis, treatment with TACI:Fc resulted in GC destruction and marked inhibition of IFN-gamma and Ig transcription. In contrast, inhibition of APRIL and BLyS in aggregate and diffuse synovitis left Ig levels unaffected and enhanced IFN-gamma production. These differential immunomodulatory effects correlated with the presence of TACI+ T cells in aggregate and diffuse synovitis and their absence in GC+ synovitis. We propose that BLyS and APRIL regulate B cell as well as T cell function and have pro- and antiinflammatory activities in RA.

Adult↗
PubMed2005

Fibrocystin interacts with CAML, a protein involved in Ca2+ signaling.

The predicted structure of the autosomal recessive polycystic kidney disease protein, fibrocystin, suggests that it may function as a receptor, but its function remains unknown. To understand its function, we searched for proteins that interact with the intracellular C-terminus of fibrocystin using the yeast two-hybrid system. From the screening, we found calcium modulating cyclophilin ligand (CAML), a protein involved in Ca(2+) signaling. Immunofluorescent analysis showed that both proteins are co-localized in the apical membrane, primary cilia, and the basal body of cells derived from the distal nephron Epitope-tagged expression constructs of both proteins were co-immunoprecipitated from COS7 cells. The intracellular C-terminus of fibrocystin interacts with CAML, a protein with an intracellular distribution that is similar to that of PKD2. Fibrocystin may participate in regulation of intracellular Ca(2+) in the distal nephron in a manner similar to PKD1 and PKD2 that are involved in autosomal dominant polycystic kidney disease.

Adaptor Proteins, Signal Transducing↗
PubMed2005

TACI-BLyS signaling via B-cell-dendritic cell cooperation is required for naive CD8+ T-cell priming in vivo.

We demonstrated that B-cell-dendritic cell (DC) interactions via transmembrane activator and calcium modulator and cyclophilin ligand (CAML) interactor (TACI) and B-lymphocyte stimulator (BLyS) provide an early signal critical to generate adequate numbers of mature antigen presenting cells (APCs) to prime naive CD8(+) T cells (CTLs) in vivo. Evidence that B cells are required for efficient CTL generation in mice and that reconstitution with wild-type but not TACI-knockout B cells restored normal CTL responses support our conclusion. Moreover, low doses of a TACI fusion protein (TACI-Fc) that express the extracellular domain of TACI (amino acid [aa] 1-126) restored CTL priming in B-cell-deficient mice in vivo and induced DC maturation in vitro. In fact, following interactions with B cells, splenic DCs rapidly express the CD86 costimulatory molecule, to an extent comparable to the exposure to antigenic stimuli. BLyS(high) peptide-pulsed bone marrow-derived DCs, used as vaccines in vivo, cannot generate CTLs in B-cell-deficient and TACI-deficient mice, strongly supporting a need for B-cell-DC cooperation through TACI-BLyS during CTL first encounter with antigens in vivo.

Animals↗
PubMed2005

TACI and BAFF-R mediate isotype switching in B cells.

The tumor necrosis factor family members BAFF and APRIL induce Ig isotype switching in human B cells. We analyzed the ability of BAFF and APRIL to induce isotype switching in murine B cells to IgG1, IgA, and IgE. APRIL and BAFF each engage two receptors, transmembrane activator and calcium-modulator and cytophilin ligand interactor (TACI) and B cell maturation antigen (BCMA), on B cells. In addition, BAFF engages a third receptor on B cells, BAFF-R. To determine the role of these receptors in isotype switching, we examined B cells from mice deficient in TACI, BCMA, and BAFF-R. The results obtained indicate that both TACI and BAFF-R are able to transduce signals that result in isotype switching.

Animals↗
PubMed2005

CAML is a p56Lck-interacting protein that is required for thymocyte development.

Calcium modulating cyclophilin ligand (CAML) is a ubiquitously expressed protein implicated in T cell signaling, although its mechanism and physiologic role in the immune system are unknown. We show here that CAML is essential for peripheral T cell development. Inactivation of CAML in mouse thymocytes lowered the numbers of double-positive and single-positive thymocytes, concomitant with reduced positive and enhanced negative selection. We found that CAML interacts with p56Lck and appears to regulate subcellular localization of the kinase in both resting and T cell receptor (TCR)-stimulated cells. CAML-deficient cells displayed enhanced p56lck and ZAP-70 phosphorylation and increased IL2 production and cell death after TCR stimulation, suggesting that CAML may act as a negative regulator of p56lck. Our data establish a novel role for CAML as an essential mediator of T cell survival during thymopoiesis and indicate that its loss deregulates p56Lck signaling.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Expression of BLyS and its receptors in B-cell non-Hodgkin lymphoma: correlation with disease activity and patient outcome.

BLyS, recently shown to be critical for survival of normal B cells, has been found to be elevated in a number of immune disease models. A role for BLyS in the survival of malignant B cells has also been revealed and we therefore sought to identify a role for BLyS and its receptors in non-Hodgkin lymphoma (NHL). We found that tumor cells from all NHL histologic subtypes expressed one or more of 3 known receptors (BCMA, TACI, and BAFF-R) for BLyS; however, the pattern of expression was variable. We provide evidence that BLyS is expressed in tumors from patients with NHL and that BLyS levels increase as tumors transform to a more aggressive phenotype. Additionally, we provide evidence that serum BLyS levels are elevated in a subgroup of patients with NHL. In patients with de novo large B-cell lymphoma, a high BLyS level correlated with a poorer median overall survival, the presence of constitutional symptoms, and elevated values of lactic dehydrogenase. When BLyS levels were correlated with response to therapy in all patients, responding patients had a significantly lower BLyS level than those with progressive disease. In summary, we found that BLyS and its receptors represent a potentially important therapeutic target in B-cell lymphoma.

Adult↗
PubMed2004

BCMA is essential for the survival of long-lived bone marrow plasma cells.

Long-lived humoral immunity is manifested by the ability of bone marrow plasma cells (PCs) to survive for extended periods of time. Recent studies have underscored the importance of BLyS and APRIL as factors that can support the survival of B lineage lymphocytes. We show that BLyS can sustain PC survival in vitro, and this survival can be further enhanced by interleukin 6. Selective up-regulation of Mcl-1 in PCs by BLyS suggests that this alpha-apoptotic gene product may play an important role in PC survival. Blockade of BLyS, via transmembrane activator and cyclophilin ligand interactor-immunoglobulin treatment, inhibited PC survival in vitro and in vivo. Heightened expression of B cell maturation antigen (BCMA), and lowered expression of transmembrane activator and cyclophilin ligand interactor and BAFF receptor in PCs relative to resting B cells suggests a vital role of BCMA in PC survival. Affirmation of the importance of BCMA in PC survival was provided by studies in BCMA-/- mice in which the survival of long-lived bone marrow PCs was impaired compared with wild-type controls. These findings offer new insights into the molecular basis for the long-term survival of PCs.

Animals↗
PubMed2003

CAML is required for efficient EGF receptor recycling.

Calcium-modulating cyclophilin ligand (CAML) is a ubiquitous protein that has been implicated in signaling from the cell surface receptor TACI in lymphocytes, although its role and mechanism of action are unknown. To study its function in the mouse, we disrupted the CAML gene and found it to be required for early embryonic development, but not for cellular viability. CAML-deficient cells have severely impaired proliferative responses to the epidermal growth factor (EGF). Although EGF-induced activation of signaling intermediates and internalization of the EGF receptor (EGFR) are normal in the absence of CAML, the recycling of internalized receptors to the plasma membrane is defective, leading to its reduced surface accumulation. We demonstrate that CAML normally associates directly with the kinase domain of the EGFR in a ligand-dependent manner. These data implicate CAML in EGFR signaling and suggest that it may play a role in receptor recycling during long-term proliferative responses to EGF.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Aberrant expression of B-lymphocyte stimulator by B chronic lymphocytic leukemia cells: a mechanism for survival.

B-cell chronic lymphocytic leukemia (B-CLL) is defined by the accumulation of CD5(+) B cells in the periphery and bone marrow. This disease is not characterized by highly proliferative cells but rather by the presence of leukemic cells with significant resistance to apoptosis and, therefore, prolonged survival. B-lymphocyte stimulator (BLyS) is a newly identified tumor necrosis factor (TNF) family member shown to be critical for maintenance of normal B-cell development and homeostasis and it shares significant homology with another TNF superfamily member, APRIL. The striking effects of BLyS on normal B-cell maintenance and survival raises the possibility that it may be involved in pathogenesis and maintenance of hematologic malignancies, including B-CLL. In this study, we investigated the status of APRIL and BLyS expression, as well as their receptors, in this disease. All B-CLL patient cells studied expressed one or more of 3 known receptors for BLyS; however, the pattern of expression was variable. In addition, we demonstrate for the first time that B-CLL cells from a subset of patients aberrantly express BLyS and APRIL mRNA, whereas these molecules were not detectable in normal B cells. Furthermore, we provide in vitro evidence that BLyS protects B-CLL cells from apoptosis and enhances cell survival. Because these molecules are key regulators of B-cell homeostasis and tumor progression, leukemic cell autocrine expression of BLyS and APRIL may be playing an important role in the pathogenesis of this disease.

Aged↗
PubMed2002

Kaposi's sarcoma-associated herpesvirus mitochondrial K7 protein targets a cellular calcium-modulating cyclophilin ligand to modulate intracellular calcium concentration and inhibit apoptosis.

On viral infection, infected cells can become the target of host immune responses or can go through a programmed cell death process, called apoptosis, as a defense mechanism to limit the ability of the virus to replicate. To prevent this, viruses have evolved elaborate mechanisms to subvert the apoptotic process. Here, we report the identification of a novel antiapoptotic K7 protein of Kaposi's sarcoma-associated herpesvirus (KSHV) which expresses during lytic replication. The KSHV K7 gene encodes a small mitochondrial membrane protein, and its expression efficiently inhibits apoptosis induced by a variety of apoptogenic agents. The yeast two-hybrid screen has demonstrated that K7 targets cellular calcium-modulating cyclophilin ligand (CAML), a protein that regulates the intracellular Ca(2+) concentration. Similar to CAML, K7 expression significantly enhances the kinetics and amplitudes of the increase in intracellular Ca(2+) concentration on apoptotic stimulus. Mutational analysis showed that K7 interaction with CAML is required for its function in the inhibition of apoptosis. This indicates that K7 targets cellular CAML to increase the cytosolic Ca(2+) response, which consequently protects cells from mitochondrial damage and apoptosis. This is a novel viral antiapoptosis strategy where the KSHV mitochondrial K7 protein targets a cellular Ca(2+)-modulating protein to confer resistance to apoptosis, which allows completion of the viral lytic replication and, eventually, maintenance of persistent infection in infected host.

Adaptor Proteins, Signal Transducing↗