CD47 Augments Fas/CD95-mediated Apoptosis

Tumoral expression of TXR1 and TSP1 predicts overall survival of patients with lung adenocarcinoma treated with first-line docetaxel-gemcitabine regimen

PURPOSE

In vitro data suggest that down-regulation of thrombospondin 1 (TSP1) expression from TXR1 is associated with resistance to taxane-based chemotherapy. The prognostic and predictive value of tumoral expression of both genes was evaluated in patients with lung adenocarcinoma treated with first-line docetaxel and gemcitabine.

EXPERIMENTAL DESIGN

Tumor samples from 96 patients, with stage IIIB (with pleural effusion) or IV lung adenocarcinomas, were analyzed for TXR1 and TSP1 mRNA levels by quantitative real-time PCR, from microdissected cells derived from patients' primary tumors.

RESULTS

The mRNA levels of the two genes were inversely correlated (Spearman's test = -0.49; P < 0.0001). Patients with low TXR1 mRNA levels experienced a longer median time to tumor progression (TTP; P < 0.0001) and median overall survival (mOS; P = 0.001) when compared with patients with high TXR1 expression. Patients with high TSP1 expression presented longer TTP (P = 0.002) and mOS (P < 0.0001) when compared with patients with low TSP1 expression. Moreover, patients with high TSP1 and low TXR1 expression (n = 36) presented higher prolonged TTP (P = 0.009) and mOS (P < 0.0001) compared with patients with high TXR1 and low TSP1 expression. Multivariate analysis showed that high TXR1/low TSP1 expression was an independent prognostic factor for decreased TTP (hazard ratio, 1.7; 95% confidence interval, 1.1-3.27; P = 0.016) and mOS (hazard ratio, 2.55; 95% confidence interval, 1.57-4.15; P < 0.0001).

CONCLUSION

These data confirm the in vitro model of TSP1 and TXR1 effect on taxane resistance in lung adenocarcinomas and merit further evaluation.

The multiple roles of the innate immune system in the regulation of apoptosis and inflammation in the brain

Central nervous system (CNS) tissues contain cells (i.e. glia and neurons) that have innate immune functions. These cells express a range of receptors that are capable of detecting and clearing apoptotic cells and regulating inflammatory responses. Phagocytosis of apoptotic cells is a nonphlogistic (i.e. noninflammatory) process that provides immune regulation through anti-inflammatory cytokines andregulatory T cells. Neurons and glia express cellular death signals, including CD95Fas/CD95L, FasL, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and tumor necrosis factor receptor 1 (TNFR), through which they can trigger apoptosis in T cells and other infiltrating cells. Microglia, astrocytes, ependymal cells, and neurons express defense collagens and scavenger and phagocytic receptors that recognize apoptotic cells displaying apoptotic cell-associated molecular patterns, which serve as markers of "altered self." Glia also express pentraxins and complement proteins (C1q, C3b, and iC3b) that opsonize apoptotic cells, making them targets for the phagocytic receptors CR3 and CR4. Immunoregulatory molecules such as the complement regulator CD46 are lost from apoptotic cells and stimulate phagocytosis, whereas the expression of CD47 and CD200 is upregulated during apoptosis; this inhibits proinflammatory microglial cytokine expression, thereby reducing the severity of inflammation. This review outlines the cellular pathways used for the detection and phagocytosis of apoptotic cells in vitro and in experimental models of CNS inflammation.

Absence of CD47 in vivo influences thymic dendritic cell subset proportions but not negative selection of thymocytes

CD47 is a ubiquitously expressed molecule which has been attributed a role in many cellular processes. Its role in preventing cellular phagocytosis has defined CD47 as an obligatory self-molecule providing a 'don't-eat-me-signal'. Additionally, CD47-CD172a interactions are important for cellular trafficking. Yet, the contribution of CD47 to T cell stimulation remains controversial, acting sometimes as a co-stimulator and sometimes as an inhibitor of TCR signalling or peripheral T cell responses. Most of the experiments leading to this controversy have been carried in in vitro systems. Moreover, the role of CD47 on thymocyte differentiation, which precisely relies on TCR signal strength, has not been evaluated. Here, we examine the in vivo role of CD47 in T cell differentiation using CD47-deficient mice. We find that, in the absence of CD47, thymocyte positive and negative selection processes are not altered. Indeed, our data demonstrate that the absence of CD47 does not influence the strength of TCR signalling in thymocytes. Furthermore, in agreement with a role for CD47-CD172a interactions in CD172a(+) dendritic cell migration, we report a reduced proportion of thymic dendritic cells expressing CD172a in CD47-deficient mice. As the total proportion of dendritic cells is maintained, this creates an imbalance in the proportion of CD172a(+) and CD172a(low) dendritic cells in the thymus. Together, these data indicate that the altered proportion of thymic dendritic cell subsets does not have a primordial influence on thymic selection processes.

Thrombospondin-1 and CD47 limit cell and tissue survival of radiation injury

Radiation, a primary mode of cancer therapy, acutely damages cellular macromolecules and DNA and elicits stress responses that lead to cell death. The known cytoprotective activity of nitric oxide (NO) is blocked by thrombospondin-1, a potent antagonist of NO/cGMP signaling in ischemic soft tissues, suggesting that thrombospondin-1 signaling via its receptor CD47 could correspondingly increase radiosensitivity. We show here that soft tissues in thrombospondin-1-null mice are remarkably resistant to radiation injury. Twelve hours after 25-Gy hindlimb irradiation, thrombospondin-1-null mice showed significantly less cell death in both muscle and bone marrow. Two months after irradiation, skin and muscle units in null mice showed minimal histological evidence of radiation injury and near full retention of mitochondrial function. Additionally, both tissue perfusion and acute vascular responses to NO were preserved in irradiated thrombospondin-1-null hindlimbs. The role of thrombospondin-1 in radiosensitization is specific because thrombospondin-2-null mice were not protected. However, mice lacking CD47 showed radioresistance similar to thrombospondin-1-null mice. Both thrombospondin-1- and CD47-dependent radiosensitization is cell autonomous because vascular cells isolated from the respective null mice showed dramatically increased survival and improved proliferative capacity after irradiation in vitro. Therefore, thrombospondin-1/CD47 antagonists may have selective radioprotective activity for normal tissues.

CD47 expression on T cell is a self-control negative regulator of type 1 immune response

The cytokine milieu and dendritic cells (DCs) direct Th1 development. Yet, the control of Th1 polarization by T cell surface molecules remains ill-defined. We here report that CD47 expression on T cells serves as a self-control mechanism to negatively regulate type 1 cellular and humoral immune responses in vivo. Th2-prone BALB/c mice that lack CD47 (CD47(-/-)) displayed a Th1-biased Ab profile at steady state and after immunization with soluble Ag. CD47(-/-) mice mounted a T cell-mediated exacerbated and sustained contact hypersensitivity (CHS) response. After their adoptive transfer to naive CD47-deficient hosts 1 day before immunization with soluble Ag, CD47(-/-) as compared with CD47(+/+)CD4(+) transgenic (Tg) T cells promoted the deviation of Ag-specific T cell responses toward Th1 that were characterized by a high IFN-gamma:IL-4 cytokine ratio. Although selective CD47 deficiency on DCs led to increased IL-12p70 production, CD47(-/-)Tg T cells produced more IFN-gamma and displayed higher T-bet expression than CD47(+/+) Tg T cells in response to OVA-loaded CD47(-/-) DCs. CD47 as part of the host environment has no major contribution to the Th1 polarization responses. We thus identify the CD47 molecule as a T cell-negative regulator of type 1 responses that may limit unwanted collateral damage to maximize protection and minimize host injury.

Patching of ganglioside(M1) in human erythrocytes - distribution of CD47 and CD59 in patched and curved membrane

Membrane rafts may act as platforms for membrane protein signalling. Rafts have also been implicated in the sorting of membrane components during membrane budding. We have studied by fluorescence microscopy cross-linking of ganglioside GM1 in the human erythrocyte membrane, and how membrane proteins CD47 and CD59 distribute in GM1 patched discoid cells and calcium-induced echinocytic cells. Patching of ganglioside(M1) (GM1) by cholera toxin subunit B (CTB) plus anti-CTB resulted in the formation of usually 40-60 GM1 patches distributed over the membrane in discoid erythrocytes. Pre-treatment of erythrocytes with methyl-beta-cyclodextrin abolished GM1 patching. GM1 patching was insensitive to pre-fixation (paraformaldehyde) of cells. Patching of GM1 did not affect the discoid shape of erythrocytes. Membrane proteins CD47 and CD59 did not accumulate into GM1 patches. No capping of patches occurred. GM1 accumulated in calcium-induced echinocytic spiculae. Also CD59, but not CD47, accumulated in spiculae. However, CD59 showed a low degree of co-localization with GM1 and frequently accumulated in different spiculae than GM1. In conclusion, our study describes a novel method for examining properties and composition of rafts. The study characterizes raft patching in the human erythrocyte membrane and emphasizes the mobility and 'echinophilicity' of GM1. Glycosyl phosphatidylinositol-anchored CD59 was identified as a mobile 'echinophilic' but 'raftophobic(GM1)' protein. Largely immobile CD47 showed no segregation.

CD47: a new target in cardiovascular therapy

CD47, originally named integrin-associated protein, is a receptor for thrombospondin-1. A number of important roles for CD47 have been defined in regulating the migration, proliferation, and survival of vascular cells, and in regulation of innate and adaptive immunity. The recent discovery that thrombospondin-1 acts via CD47 to inhibit nitric oxide signaling throughout the vascular system has given new importance and perhaps a unifying mechanism of action to these enigmatic proteins. Here we trace the development of this exciting new paradigm for CD47 function in vascular physiology.

The matrix metalloproteinases and CNS plasticity: an overview

The matrix metalloproteinases (MMPs) are expressed in response to pro-inflammatory stimuli and other triggers. The MMPs cleave numerous substrates including extracellular matrix components, cytokines and growth factors. In the CNS, while most studied in the context of disease, the many physiological functions of the MMPs are now becoming appreciated. This review provides an overview of the growing body of evidence for physiological roles of MMPs both in CNS development and in CNS plasticity in normal brain functioning, including learning and memory, as well as in CNS repair and reorganization as part of the neuroimmune response to injury.

Interactions between CD47 and Thrombospondin Reduce Inflammation

CD47 on the surface of T cells was shown in vitro to mediate either T cell activation or, in the presence of high amounts of thrombospondin (TSP), T cell apoptosis. We report here that CD47-deficient mice, as well as TSP-1 or TSP-2-deficient mice, sustain oxazolone-induced inflammation for more than four days, whereas wild-type mice reduce the inflammation within 48 h. We observe that prolonged inflammation in CD47-, TSP-1-, or TSP-2-deficient mice is accompanied by a local deficiency of T cell apoptosis. Finally, we show that upon activation normal T cells increase the expression of the proapoptotic Bcl-2 family member BNIP3 (Bcl-2/adenovirus E1B 19-kDa interacting protein) and undergo CD47-mediated apoptosis. This finding is consistent with our previous demonstration of a physical interaction between BNIP3 and CD47 that inhibits BNIP3 degradation by the proteasome, sensitizing T cells to CD47-induced apoptosis. Overall, these results reveal an important role in vivo for this new CD47/BNIP3 pathway in limiting inflammation by controlling the number of activated T cells.

Osteoclast formation is strongly reduced both in vivo and in vitro in the absence of CD47/SIRPalpha-interaction

Physical interaction between the cell surface receptors CD47 and signal regulatory protein alpha (SIRPalpha) was reported to regulate cell migration, phagocytosis, cytokine production, and macrophage fusion. However, it is unclear if the CD47/SIRPalpha-interaction can also regulate macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor (NF)-kappaB ligand (RANKL)-stimulated formation of osteoclasts. Here, we show that functional blocking antibodies to either CD47 or SIRPalpha strongly reduced formation of multinucleated tartrate-resistant acid phosphatase (TRAP)+ osteoclasts in cultures of murine hematopoietic cells, stimulated in vitro by M-CSF and RANKL. In addition, the numbers of osteoclasts formed in M-CSF/RANKL-stimulated bone marrow macrophage cultures from CD47-/- mice were strongly reduced, and bones of CD47-/- mice exhibited significantly reduced osteoclast numbers, as compared with wild-type controls. We conclude that the CD47/SIRPalpha interaction is important for M-CSF/RANKL-stimulated osteoclast formation both in vivo and in vitro, and that absence of CD47 results in decreased numbers of osteoclasts in CD47-/- mice.

Mechanism of synergy between T cell signals and C8-substituted guanine nucleosides in humoral immunity: B lymphotropic cytokines induce responsiveness to 8-mercaptoguanosine

B lymphocytes require a source of T cell-like help to produce antibody to T cell-dependent antigens. T cell-derived lymphokines and C8-substituted guanine ribonucleosides (such as 8-mercaptoguanosine; 8MGuo) are effective sources of such T cell-like help. Addition of T cell-derived lymphokines to antigen-activated B cells together with 8MGuo results in synergistic B cell differentiation, amplifying the sum of the individual responses twofold to four-fold. Lymphokine activity is required at initiation of culture for optimal synergy with 8MGuo, whereas the nucleoside can be added up to 48 hr after the lymphokines with full synergy. 8MGuo provides a perceived T cell-like differentiation signal to B cells from immunodeficient xid mice, thereby distinguishing a subset of Lyb-5- nucleoside-responsive B cells from those activated by soluble anti-mu followed by B cell stimulatory factor-1, interleukin 1, and B cell differentiation factors, which are Lyb-5+. Moreover, at least a subset of the B cells recruited by the synergistic interaction of lymphokines and nucleoside is distinct from that responsive to 8MGuo + antigen, insofar as Sephadex G-10 nonadherent xid B cells fail to respond to either 8MGuo or lymphokines alone, but do respond to the combination. A distinct subpopulation can also be demonstrated among normal B cells by limiting dilution analysis in which the precursor frequency of antigen-reactive B cells in the presence of lymphokines or nucleoside alone increases substantially when both agents are present together. In concert with the kinetic data, these observations suggest that synergy derives at least in part from the ability of lymphokines to induce one or more elements the absence of which limits the capacity of a distinct B cell subpopulation to respond to 8MGuo.