Downregulation of NK cell-mediated swine endothelial cell lysis by DAF (CD55)

MicroRNAs Affect Complement Regulator Expression and Mitochondrial Activity to Modulate Cell Resistance to Complement-Dependent Cytotoxicity

MicroRNAs (miR) are small RNA molecules that shape the cell transcriptome and proteome through regulation of mRNA stability and translation. Here, we examined their function as determinants of cell resistance to complement-dependent cytotoxicity (CDC). To achieve this goal, we compared the expression of microRNAs between complement-resistant and -sensitive K562 leukemia, Raji lymphoma, and HCT-116 colorectal carcinoma cells. Global microRNA array analysis identified miR-150, miR-328, and miR-616 as regulators of CDC resistance. Inhibition of miR-150 reduced resistance, whereas inhibition of miR-328 or miR-616 enhanced cell resistance. Treatment of K562 cells with a sublytic dose of complement was shown to rapidly increase miR-150, miR-328, and miR-616 expression. Protein targets of these microRNAs were analyzed in K562 cells by mass spectrometry-based proteomics. Expression of the complement membrane regulatory proteins CD46 and CD59 was significantly enhanced after inhibition of miR-328 and miR-616. Enrichment of proteins of mitochondria, known target organelles in CDC, was observed after miR-150, miR-328, and miR-616 inhibition. In conclusion, miR-150, miR-328, and miR-616 regulate cell resistance to CDC by modifying the expression of the membrane complement regulators CD46 and CD59 and the response of the mitochondria to complement lytic attack. These microRNAs may be considered targets for intervention in complement-associated diseases and in anticancer, complement-based therapy.

Downregulation of membrane complement inhibitors CD55 and CD59 by siRNA sensitises uterine serous carcinoma overexpressing Her2/neu to complement and antibody-dependent cell cytotoxicity in vitro: implications for trastuzumab-based immunotherapy

Background:

We evaluated the expression of CD46, CD55 and CD59 membrane-bound complement-regulatory proteins (mCRPs) in primary uterine serous carcinoma (USC) and the ability of small interfering RNA (siRNA) against these mCRPs to sensitise USC to complement-dependent cytotoxicity (CDC) and antibody (trastuzumab)-dependent cellular cytotoxicity (ADCC) in vitro.

Methods:

Membrane-bound complement-regulatory proteins expression was evaluated using real-time PCR (RT–PCR) and flow cytometry, whereas Her2/neu expression and c-erbB2 gene amplification were assessed using immunohistochemistry, flow cytometry and fluorescent in-situ hybridisation. The biological effect of siRNA-mediated knockdown of mCRPs on HER2/neu-overexpressing USC cell lines was evaluated in CDC and ADCC 4-h chromium-release assays.

Results:

High expression of mCRPs was found in USC cell lines when compared with normal endometrial cells (P<0.05). RT–PCR and FACS analyses demonstrated that anti-mCRP siRNAs were effective in reducing CD46, CD55 and CD59 expression on USC (P<0.05). Baseline complement-dependent cytotoxicity (CDC) against USC cell lines was low (mean±s.e.m.=6.8±0.9%) but significantly increased upon CD55 and CD59 knockdown (11.6±0.8% and 10.7±0.9%, respectively, P<0.05). Importantly, in the absence of complement, both CD55 and CD59, but not CD46, knockdowns significantly augmented ADCC against USC overexpressing Her2/neu.

Conclusion:

Uterine serous carcinoma express high levels of the mCRPs CD46, CD55 and CD59. Small interfering RNA inhibition of CD55 and CD59, but not CD46, sensitises USC to both CDC and ADCC in vitro, and if specifically targeted to tumour cells, may significantly increase trastuzumab-mediated therapeutic effect in vivo.

Decay-accelerating factor (CD55): a versatile acting molecule in human malignancies

The decay-accelerating factor (DAF, CD55) physiologically serves as an inhibitor of the complement system. Moreover, DAF is broadly expressed in malignant tumors. Here, DAF seems to dispose of several different functions reaching far beyond its immunological role, e.g., promotion of tumorigenesis, decrease of complement mediated tumor cell lysis, autocrine loops for cell rescue and evasion of apoptosis, neoangiogenesis, invasiveness, cell motility, and metastasis via oncogenic tyrosine kinase pathway activation, and specific seven-span transmembrane receptors (CD97) binding. Furthermore, DAF has already been included in diagnostic or therapeutic studies. Thereby, studies applying monoclonal anti-DAF antibodies and anti-DAF vaccination for a targeted therapy have been enrolled recently.

Expression of glycosylphosphatidylinositol-anchored CD59 on target cells enhances human NK cell-mediated cytotoxicity

NK cell-mediated cytotoxicity of target cells is the result of a balance between the activating and inhibitory signals provided by their respective ligand-receptor interactions. In our current study, we have investigated the significance of CD59 on human target cells in modulating this process. A range of CD59 site-specific Abs were used in NK cytotoxicity blocking studies against the CD59-expressing K562 target cell line. Significantly reduced cytotoxicity was observed in the presence of Abs previously shown to lack blocking capacity for C-mediated lysis. We investigated the consequences for alternative membrane attachment modalities, namely bis-myristoylated-peptidyl (BiMP) and GPI anchoring, on CD59-negative U937 cells. Expression of GPI-anchored CD59 either via transfection or incorporation rendered U937 targets more susceptible to NK cytotoxicity, whereas incorporation of CD59 via a BiMP anchor to similar levels did not alter susceptibility to NK cytotoxicity. Localization of both BiMP- and GPI-anchored CD59 proteins was shown to be within the lipid raft microdomain. A role for the GPI anchor and independence from glycosylation status was confirmed by expression of transmembrane-anchored CD59 or unglycosylated CD59 and by testing in NK cytotoxicity assays. To investigate mechanisms, we compared the signaling capacity of the various forms of expressed and incorporated CD59 following Ab cross-linking in calcium flux assays. GPI-anchored CD59, with or without glycosylation, mediated activation events, whereas CD59 forms lacking the GPI anchor did not. The data show that the increased susceptibility of target cells expressing CD59 to NK cytotoxicity requires GPI anchor-mediating signaling events, likely mediated by interactions between GPI-anchored CD59 on targets and NK receptors.

Expression profiling of murine double-negative regulatory T cells suggest mechanisms for prolonged cardiac allograft survival

Recent studies have demonstrated that both mouse and human alpha beta TCR(+)CD3(+)NK1.1(-)CD4(-)CD8- double-negative regulatory T (DN Treg) cells can suppress Ag-specific immune responses mediated by CD8+ and CD4+ T cells. To identify molecules involved in DN Treg cell function, we generated a panel of murine DN Treg clones, which specifically kill activated syngeneic CD8+ T cells. Through serial cultivation of DN Treg clones, mutant clones arose that lost regulatory capacity in vitro and in vivo. Although all allogeneic cardiac grafts in animals preinfused with tolerant CD4/CD8 negative 12 DN Treg clones survived over 100 days, allograft survival is unchanged following infusion of mutant clones (19.5 +/- 11.1 days) compared with untreated controls (22.8 +/- 10.5 days; p < 0.001). Global gene expression differences between functional DN Treg cells and nonfunctional mutants were compared. We found 1099 differentially expressed genes (q < 0.025%), suggesting increased cell proliferation and survival, immune regulation, and chemotaxis, together with decreased expression of genes for Ag presentation, apoptosis, and protein phosphatases involved in signal transduction. Expression of 33 overexpressed and 24 underexpressed genes were confirmed using quantitative real-time PCR. Protein expression of several genes, including Fc epsilon RI gamma subunit and CXCR5, which are >50-fold higher, was also confirmed using FACS. These findings shed light on the mechanisms by which DN Treg cells down-regulate immune responses and prolong cardiac allograft survival.