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1.  The unique cytoplasmic domain of human FcγRIIIA regulates receptor mediated function 
Ligand specificity characterizes receptors for antibody and many other immune receptors, but the common use of the FcR-γ-chain as their signaling subunit challenges the concept that these receptors are functionally distinct. We hypothesized that elements for specificity might be determined by the unique cytoplasmic domain (CY) sequences of the ligand-binding α-chains of γ-chain associated receptors. Among Fcγ receptors (FcRs), a protein kinase C (PKC) phosphorylation consensus motif, [RSSTR], identified within the FcγRIIIa (CD16A) CY by in silico analysis, is specifically phosphorylated by PKCs, unlike other FcRs. Phosphorylated CD16A mediates a more robust calcium flux, tyrosine phosphorylation of Syk and pro-inflammatory cytokine production while non-phosphorylatable CD16A is more effective at activation of the Gab2/PI3K pathway, leading to enhanced degranulation. S100A4, a specific protein binding partner for CD16A-CY newly identified by yeast two-hybrid analysis, inhibits phosphorylation of CD16A-CY by PKC in vitro, and reduction of S100A4 levels in vivo enhances receptor phosphorylation upon cross-linking. Taken together, PKC-mediated phosphorylation of CD16A modulates distinct signaling pathways engaged by the receptor. Calcium activated binding of S100A4 to CD16A, promoted by the initial calcium flux, attenuates the phosphorylation of CY, and acting as a molecular switch, may both serve as a negative feedback on cytokine production pathways during sustained receptor engagement and favor a shift to degranulation, consistent with the importance of granule release following conjugate formation between CD16A+ effector cells and target cells. This switch mechanism points to new therapeutic targets and provides a frame for understanding novel receptor polymorphisms.
doi:10.4049/jimmunol.1200704
PMCID: PMC3478424  PMID: 23024279
2.  FAS mRNA editing in human Systemic Lupus Erythematosus 
Human mutation  2011;32(11):1268-1277.
FAS/FASL system plays a central role in maintaining peripheral immune tolerance. Human SLE is a prototypic systemic autoimmune disease characterized by expansion of autoreactive lymphocytes. It remains unclear whether a defective FAS/FASL system is involved in the pathogenesis of SLE. In this study, we have discovered a novel nucleotide insertion in FAS mRNA. We demonstrate that this novel FAS mutation occurs at mRNA levels, likely through a site-specific mRNA editing process. The mRNA editing mutation is unique for human FAS because the similar mRNA editing event is absent in other human TNFR family genes with death domains (DR5, DR6, and TNFR1) and in murine FAS. The adenine insertion mutation in the coding region message causes the alteration of human FAS mRNA reading frame. Functionally, cells expressing the edited FAS (edFAS) were refractory to FAS-mediated apoptosis. Surprisingly, cells from SLE patients produced significantly more edFAS products compared to cells from normal healthy controls. Additionally, we demonstrated that persistent engagement of T cell receptor increases human FAS mRNA editing in human T cells. Our data suggest that the site-specific FAS mRNA editing mutation may play a critical role in human immune responses and in the pathogenesis of human chronic inflammatory diseases.
doi:10.1002/humu.21565
PMCID: PMC3196739  PMID: 21793106
FAS; mRNA editing; apoptosis; Systemic Lupus Erythematosus
3.  Human FasL Gene Is a Target of β-Catenin/T-Cell Factor Pathway and Complex FasL Haplotypes Alter Promoter Functions 
PLoS ONE  2011;6(10):e26143.
FasL expression on human immune cells and cancer cells plays important roles in immune homeostasis and in cancer development. Our previous study suggests that polymorphisms in the FasL promoter can significantly affect the gene expression in human cells. In addition to the functional FasL SNP -844C>T (rs763110), three other SNPs (SNP -756A>G or rs2021837, SNP -478A>T or rs41309790, and SNP -205 C>G or rs74124371) exist in the proximal FasL promoter. In the current study, we established three major FasL hyplotypes in humans. Interestingly, a transcription motif search revealed that the FasL promoter possessed two consensus T-cell factor (TCF/LEF1) binding elements (TBEs), which is either polymorphic (SNP -205C>G) or close to the functional SNP -844C>T. Subsequently, we demonstrate that both FasL TBEs formed complexes with the TCF-4 and β-catenin transcription factors in vitro and in vivo. Co-transfection of LEF-1 and β-catenin transcription factors significantly increased FasL promoter activities, suggesting that FasL is a target gene of the β-catenin/T-cell factor pathway. More importantly, we found that the rare allele (-205G) of the polymorphic FasL TBE (SNP -205C>G) failed to bind the TCF-4 transcription factor and that SNP -205 C>G significantly affected the promoter activity. Furthermore, promoter reporter assays revealed that FasL SNP haplotypes influenced promoter activities in human colon cancer cells and in human T cells. Finally, β-catenin knockdown significantly decreased the FasL expression in human SW480 colon cancer cells. Collectively, our data suggest that β-catenin may be involved in FasL gene regulation and that FasL expression is influenced by FasL SNP haplotypes, which may have significant implications in immune response and tumorigenesis.
doi:10.1371/journal.pone.0026143
PMCID: PMC3191176  PMID: 22022540
5.  Expression Profile of FcγRIIb on Leukocytes and Its Dysregulation in Systemic Lupus Erythematosus1 
FcγRIIb (CD32B, Online Mendelian Inheritance in Man 604590), an IgG FcR with a tyrosine-based inhibitory motif, plays a critical role in the balance of tolerance and autoimmunity in murine models. However, the high degree of homology between FcγRIIb and FcγRIIa in humans and the lack of specific Abs to differentiate them have hampered study of the normal expression profile of FcγRIIb and its potential dysregulation in autoimmune diseases such as systemic lupus erythematosus (SLE). Using our newly developed anti-FcγRIIb mAb 4F5 which does not react with FcγRIIa, we found that FcγRIIb is expressed on the cell surface of circulating B lymphocytes, monocytes, neutrophils, myeloid dendritic cells (DCs), and at very low levels on plasmacytoid DCs from some donors. Normal donors with the less frequent 2B.4 promoter haplotype have higher FcγRIIb expression on monocytes, neutrophils, and myeloid DCs similar to that reported for B lymphocytes, indicating that FcγRIIb expression on both myeloid and lymphoid cells is regulated by the naturally occurring regulatory single nucleotide polymorphisms in the FCGR2B promoter. FcγRIIb expression in normal controls is up-regulated on memory B lymphocytes compared with naive B lymphocytes. In contrast, in active SLE, FcγRIIb is significantly down-regulated on both memory and plasma B lymphocytes compared with naive and memory/plasma B lymphocytes from normals. Similar down-regulation of FcγRIIb on myeloid-lineage cells in SLE was not seen. Our studies demonstrate the constitutive regulation of FcγRIIb by natural gene polymorphisms and the acquired dysregulation in SLE autoimmunity, which may identify opportunities for using this receptor as a therapeutic target.
PMCID: PMC2824439  PMID: 17312177

Results 1-5 (5)