Signal transduction via both human low-affinity IgG Fc receptors, Fc gamma RIIa and Fc gamma RIIIb, depends on the activity of different families of intracellular kinases

Identification of important genes associated with acute myocardial infarction using multiple cell death patterns

Acute myocardial infarction (AMI) is a global health threat, and programmed cell death (PCD) plays a crucial role in its occurrence and development. In this study, integrated bioinformatics tools were used to explore new biomarkers and therapeutic targets in AMI. Thirteen types of PCD-related genes were identified through literature review, KEGG, and GSEA pathways. Gene expression matrices and clinical data from AMI patients and healthy controls were obtained from the GEO database. Statistical analysis in R identified 377 differentially expressed genes in AMI patients. Intersection analysis between the differentially expressed genes and PCD-related genes revealed 24 genes positively correlated with immune cells such as Neutrophils and Monocytes, while negatively correlated with T cells CD4 memory resting and Plasma cells. Unsupervised clustering analysis divided patients into two groups (C1 and C2) based on the expression levels of these 24 genes. GSVA analysis showed that C2 patients were more active in pathways related to maintaining normal cell morphology and promoting phagocytosis, suggesting a lower programmed cell death rate and a higher tendency to maintain cell survival. Two hub genes, TNFAIP3 and TP53INP2, were identified through LASSO regression analysis and SVM-RFE, and were validated using an external dataset and RT-qPCR、Western blot and ELISA analysis. These hub genes showed significantly higher expression and protein secretion levels in AMI patients compared to healthy individuals. Overall, regulating and controlling PCD, particularly through the identified hub genes, TNFAIP3 and TP53INP2, may provide new therapeutic strategies for improving the prognosis of AMI patients and preventing heart failure.

Human neutrophils mediate trogocytosis rather than phagocytosis of CLL B cells opsonized with anti-CD20 antibodies

Polymorphonuclear neutrophils (PMNs) have previously been reported to mediate phagocytosis of anti-CD20-opsonized B cells from patients with chronic lymphocytic leukemia (CLL). However, recent data have suggested that PMNs, like macrophages, can also mediate trogocytosis. We have performed experiments to more precisely investigate this point and to discriminate between trogocytosis and phagocytosis. In live-cell time-lapse microscopy experiments, we could not detect any significant phagocytosis by purified PMNs of anti-CD20-opsonized CLL B cells, but could detect only the repeated close contact between effectors and targets, which suggested trogocytosis. Similarly, in flow cytometry assays using CLL B-cell targets labeled with the membrane dye PKH67 and opsonized with rituximab or obinutuzumab, we observed that a mean of 50% and 75% of PMNs had taken a fraction of the dye from CLL B cells at 3 and 20 hours, respectively, with no significant decrease in absolute live or total CLL B-cell numbers, confirming that trogocytosis occurs, rather than phagocytosis. Trogocytosis was accompanied by loss of membrane CD20 from CLL B cells, which was evident with rituximab but not obinutuzumab. We conclude that PMNs mediate mostly trogocytosis rather than phagocytosis of anti-CD20-opsonized CLL B cells, and we discuss the implications of this finding in patients with CLL treated with rituximab or obinutuzumab in vivo.

Glycoengineered CD20 antibody obinutuzumab activates neutrophils and mediates phagocytosis through CD16B more efficiently than rituximab

Phagocytosis of CLL targets by neutrophils is a novel mechanism of action of the glycoengineered anti-CD20 antibody obinutuzumab. This mechanism takes place in physiological conditions and requires CD16B and CD32A.

Involvement of Fc receptors in disorders of the central nervous system

Immunoglobulins are proteins with a highly variable antigen-binding domain and a constant region (Fc domain) that binds to a cell surface receptor (FcR). Activation of FcRs in immune cells (lymphocytes, macrophages, and mast cells) triggers effector responses including cytokine production, phagocytosis, and degranulation. In addition to their roles in normal responses to infection or tissue injury, and in immune-related diseases, FcRs are increasingly recognized for their involvement in neurological disorders. One or more FcRs are expressed in microglia, astrocytes, oligodendrocytes, and neurons. Aberrant activation of FcRs in such neural cells may contribute to the pathogenesis of major neurodegenerative conditions including Alzheimer's disease, Parkinson's disease, ischemic stroke, and multiple sclerosis. On the other hand, FcRs may play beneficial roles in counteracting pathological processes; for e.g., FcRs may facilitate removal of amyloid peptides from the brain and so protect against Alzheimer's disease. Knowledge of the functions of FcRs in the nervous system in health and disease is leading to novel preventative and therapeutic strategies for stroke, Alzheimer's disease, and other neurological disorders.

Cytotoxic activity of gemtuzumab ozogamicin (Mylotarg) in acute myeloid leukemia correlates with the expression of protein kinase Syk

Acute myeloid leukemia (AML) cells express the cell surface antigen CD33 that, upon ligation with a monoclonal antibody (mAb), is a downregulator of cell growth in a Syk-dependent manner. An anti-CD33 mAb coupled to a toxin, gemtuzumab ozogamicin (GO), is used for the treatment of AML (Mylotarg). Therefore, we investigated whether the response of AML cells to GO treatment also depends on Syk expression. Forty primary AML samples (25 Syk-positive and 15 Syk-negative) were tested for their response to the anti-proliferative effects of GO and unmodified anti-CD33 mAb. A correlation between Syk expression and the response of leukemia cells to GO and anti-CD33 mAb was found. 'Blocking' of Syk by small interfering RNA resulted in unresponsiveness of AML cells to both GO and anti-CD33 mAb-mediated cytotoxicity. Syk upregulation by the de-methylating agent 5-azacytidine (5-aza) induced re-expression of Syk in some cases, resulting in enhanced GO and anti-CD33-mediated inhibition of leukemia cell growth. Thus, the cytotoxicity of both GO and anti-CD33 in primary AML samples was associated with Syk expression. 5-Aza restored Syk and increased the sensitivity of originally Syk-negative, non-responsive cells to CD33 ligation to levels of Syk-positive cells. These data have clinical significance for predicting response to GO and designing clinical trials.

Anti-CD33 monoclonal antibodies enhance the cytotoxic effects of cytosine arabinoside and idarubicin on acute myeloid leukemia cells through similarities in their signaling pathways

OBJECTIVE

Chemotherapy agents (CA) such as cytosine arabinoside (ara-C), idarubicin (IDA), and etoposide (VP-16) are widely used in the treatment of acute myeloid leukemia (AML) However, their effects on signaling pathways leading to cytotoxicity have only been described recently. Ligation of the leukemia-associated antigen CD33 by anti-CD33 monoclonal antibody (mAb) also results in signaling events that induce a downregulation of cell growth. We examined the possibility that anti-CD33 mAb and CA might cooperate in mediation of growth inhibition in primary AML samples and AML cell lines.

MATERIALS AND METHODS

We investigated two AML cells lines and 14 primary AML samples for their proliferative response ((3)H-thymidine incorporation), colony formation, and biochemical (Western blot analysis) to anti-CD33 mAb treatment combined with chemotherapy agents.

RESULTS

CD33 ligation induced a significant increase in ara-C- or IDA- but not VP-16-or Bryostatin-mediated inhibition of proliferation and colony formation. Ara-C and IDA induced SHP-1 and SHP-2 protein tyrosine phosphatase (PTPs) phosphorylation and Lyn/SHP-1 complex formation, while VP-16 and Bryostatin did not. CD33 ligation, however, mediated phosphorylation of these PTPs and Syk/SHP-1 complex formations. Combined treatment of AML cells by ara-C or IDA with anti-CD33 mAb resulted in higher levels of SHP-1 phosphorylation. Reduction in SHP-1 by short interfering RNA abrogated these effects.

CONCLUSION

These data suggest that combined incubation of leukemia cells with anti-CD33 mAb and ara-C or IDA, but not VP-16 or Bryostatin, independently triggers similar events in the downstream signaling cascade, and therefore leads to additive antiproliferative effects and enhanced cytotoxicity.

Monosodium urate monohydrate crystals induce the release of the proinflammatory protein S100A8/A9 from neutrophils

The neutrophil cytoplasmic protein S100A8/A9 (along with S100A8 and S100A9) is chemotactic and stimulates neutrophil adhesion by activating the beta2-integrin CD11b/CD18. It is also essential to neutrophil migration in vivo in response to monosodium urate monohydrate (MSUM) crystals, the principal etiologic agent of gout. S100A8/A9 is present in the synovial fluid of patients with gout and arthritis and is secreted by activated monocytes; however, its mechanism of release by neutrophils remains unknown. The aim of this study was to identify the mechanism of stimulation of the release of S100A8/A9 by MSUM-activated neutrophils. Here, we show that S100A8/A9 is released by neutrophils stimulated with MSUM crystals and that this release could be enhanced by preincubating neutrophils with granulocyte macrophage-colony stimulating factor. Antibodies directed against CD11b and CD16 blocked the release induced by MSUM crystals, suggesting that Fc receptor for immunoglobulin G (FcgammaR)IIIB (CD16) and CD11b/CD18 were involved in the stimulation by MSUM crystals. Neutrophil preincubation with the Src kinase inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl) pyrazolo[3,4-d]pyrimidine and the Syk tyrosine kinase inhibitor trans-3,3',4,5'-tetrahydrozystilbene significantly reduced the release of S100A8/A9, suggesting that the Src tyrosine kinase family and Syk were involved. In addition, wortmannin reduced neutrophil release of S100A8/A9, indicating a potential involvement of phosphatidylinolitol-3 kinase in this release. Preincubation of neutrophils with the tubulin depolymerization promoters nocodazole and vincristine reduced MSUM-induced release, suggesting a tubulin-associated pathway of release. These results indicate that S100A8/A9 is released by MSUM crystal-stimulated neutrophils following activation of CD11b, CD16, Src kinases, Syk, and tubulin polymerization.

The inhibitory effect of anti-CD33 monoclonal antibodies on AML cell growth correlates with Syk and/or ZAP-70 expression

OBJECTIVES

Acute myeloid leukemia (AML) cells express the cell surface antigen CD33 that can function as a downregulator of cell growth, mediating growth arrest and apoptosis. The protein kinase Syk is an essential element in several cascades coupling certain antigen receptors to cell responses. Recently we reported that CD33 recruits Syk for its signaling in AML cell lines. In this study, we further investigated the mechanism(s) of Syk engagement in CD33 signaling in primary AML samples.

METHODS

We investigated 25 primary AML samples for their proliferative response (3H-thymidine incorporation) and biochemical changes (Western blot analysis) to anti-CD33 mAb treatment.

RESULTS

Proliferation studies demonstrated that 14 (56%) of AML samples were responsive (R) while 11 (44%) were nonresponsive (n-R) to inhibitory antibody activity. Seven of 25 AML samples (28%) expressed undetectable levels of Syk. However, cells from two of these patients expressed the ZAP-70 protein kinase. In Syk/ZAP-70(+) samples, CD33 ligation inhibited proliferation in 70% of cases, while none of the Syk/ZAP-70(-) samples was responsive. There were significant biochemical differences between responder and nonresponder AML populations. In responder samples, CD33 ligation induced phosphorylation of CD33 andSyk and formation of the CD33/Syk complex. In nonresponder samples, CD33 was not phosphorylated, and Syk was in complex with the SHP-1 protein phosphatase constitutively.

CONCLUSIONS

Syk is an important component in the regulation of proliferation in AML cells. The differential response of AML cells to CD33 ligation is associated with the level of the Syk expression.

Signals mediated by FcgammaRIIA suppress the growth of B-lineage acute lymphoblastic leukemia cells

We examined Fc receptor expression and function in normal and leukemic human immature B cells. Fc receptor expression increased with normal B cell maturation: CD32(+) cells composed 8.1% +/- 1.2% (mean +/- s.d.) of the least mature (CD34(+)CD10(+)), 19.2% +/- 5.7% of intermediate (CD34(-)CD10(+)), and 82.4% +/- 5.0% of mature (CD34(-)CD10(-)) bone marrow CD19(+) B cells. Forty-five of 57 primary B-lineage acute lymphoblastic leukemia samples and all six cell lines studied expressed Fc receptors. By RT-PCR and antibody staining, FcgammaRIIA was the Fc receptor predominantly expressed in these cells. FcgammaRIIA ligation in RS4;11 and 380 cells induced tyrosine phosphorylation of CD32, CD19, CBL, SYK, P13-K p85 and SHIP, as well as RasGAP association with tyrosine-phosphorylated p62(dok). These signalling events resulted in a marked suppression of leukemia cell growth. After a 7-day exposure to anti-CD32, the recovery of ALL cells cocultured with stroma was reduced to 5.5% +/- 2.8% of control values in 380 cells (n = 14), 19.4% +/- 6.1% (n = 8) in RS4;11, and 4.0% +/- 1.3% (n = 6) in KOPN55bi. CD32 ligation also reduced cell recovery in five of seven CD32(+) primary leukemia samples. Thus, FcgammaRIIA mediates signals that suppress the growth of lymphoid leukemia cells.