Opposite ability of pre-TCR and alpha beta TCR to induce apoptosis

Structural Perspective of NR4A Nuclear Receptor Family and Their Potential Endogenous Ligands

There are 48 nuclear receptors in the human genome, and many members of this superfamily have been implicated in human diseases. The NR4A nuclear receptor family consisting of three members, NR4A1, NR4A2, and NR4A3 (formerly annotated as Nur77, Nurr1, and NOR1, respectively), are still orphan receptors but exert pathological effects on immune-related and neurological diseases. We previously reported that prostaglandin A1 (PGA1) and prostaglandin A2 (PGA2) are potent activators of NR4A3, which bind directly to the ligand-binding domain (LBD) of the receptor. Recently, the co-crystallographic structures of NR4A2-LBD bound to PGA1 and PGA2 were reported, followed by reports of the neuroprotective effects of these possible endogenous ligands in mouse models of Parkinson's disease. Based on these structures, we modeled the binding structures of the other two members (NR4A1 and NR4A3) with these potential endogenous ligands using a template-based modeling method, and reviewed the similarity and diversity of ligand-binding mechanisms in the nuclear receptor family.

Microarray analysis identifies altered regulation of nuclear receptor family members in the pre-disease state of multiple sclerosis

Molecular mechanisms that influence susceptibility to multiple sclerosis are poorly understood. We analyzed peripheral blood gene expression profiles in nine healthy subjects up to nine years before the onset of multiple sclerosis in comparison with 11 age-, gender-, and origin-matched healthy subjects who remained multiple sclerosis-free, and 31 subjects during the first clinical episode of multiple sclerosis. Within the 1051 highly variable genes that differentiated between multiple sclerosis-to-be and multiple sclerosis-free subjects, we identified activation of TCR signaling that triggered the Cbl and MAPK cascade in concert with downstream synergic over-expression of NFAT and MEF2B, but failed to augment the expression of the nuclear receptor gene family members NR4A1, NR2F1, VDR and MEF2B, that further resulted in impaired apoptotic machinery. Comparison between multiple sclerosis-to-be and first clinical onset of multiple sclerosis operating module networks demonstrated the evolution of altered regulation of nuclear receptor-dependent apoptosis. Our findings demonstrating a silent multiple sclerosis trait that is associated with suppressed expression of the nuclear receptor network and inhibited apoptosis of activated T-cells support the role of these transcription signals in the evolution of the autoimmune processes that operate in the pre-disease stage of multiple sclerosis.

The NR4A nuclear receptor family in eosinophils

It is well-known that many members of the family of nuclear receptors have been implicated in human diseases, and metabolic disorders in particular. The NR4A nuclear receptor family consists of three members, Nur77, Nurr1, and NOR1. All of these are orphan receptors, and Nur77 and NOR1 exert possible pathological roles in immune diseases through the modulation of leukocyte functions. CD30 stimulation, which induces eosinophil-specific apoptosis, markedly enhances expression of Nur77 and NOR1 in eosinophils. This suggests the possibility of pharmacological modulation of Nur77- or NOR1-specific apoptotic pathways via receptor-dependent transactivation. In this review, we discuss treatment of allergic diseases by low molecular weight compounds acting through the NR4A receptor family to cause eosinophil apoptosis. NR4A nuclear receptor genes were selected following comprehensive analysis of differentially expressed genes in eosinophils of atopic dermatitis patients compared with healthy volunteers.

Prostaglandin A2 acts as a transactivator for NOR1 (NR4A3) within the nuclear receptor superfamily

Within the nuclear receptor superfamily, Nur77, Nurr1, and NOR1 constitute the nuclear receptor subfamily 4 group A. Modulation of NOR1 function would be therapeutic potential for diseases related to dysfunction of NOR1, including extraskeletal myxoid chondrosarcoma and autoimmune diseases. By screening arachidonate metabolites for their capacity of transcriptional activation, we have identified prostaglandin (PG) A2 as a transactivator for NOR1. PGA2 acted as a potent activator of NOR1-dependent transcription through the GAL4-based reporter system. The putative ligand-binding domain (LBD) of the receptor directly bound PGA2, and LBD-deleted receptor showed little transcriptional activation by PGA2. Primary cultured spleen cells derived from transgenic mice overexpressing NOR1, showed higher sensitivity to PGA2 compared to those from wild-type mice. These observations suggest that PGA2 can serve as a transactivator of NOR1, and thus suggest a possibility of pharmacological modulation of the NOR1 pathways by PGA2-related compounds.

NR4A orphan nuclear receptor family in peripheral blood eosinophils from patients with atopic dermatitis and apoptotic eosinophils in vitro

To identify novel genes related to the clinical signs of atopic dermatitis (AD), differentially expressed genes were sought in peripheral blood eosinophils from both AD patients and healthy volunteers. RNA was prepared from eosinophils, expression of various genes was monitored using the Affymetrix GeneChip, and expression was quantified by real-time RT-PCR. Two genes, Nur77 and NOR1, members of NR4A orphan nuclear receptor family, were expressed at a significantly higher level in AD patients than in healthy volunteers. Expression of another gene in the NR4A receptor family, Nurr1, was also higher in AD patients than in healthy volunteers. When peripheral blood leukocytes from healthy volunteers were fractionated, NOR1 expression was highest in eosinophils, but expression of Nur77 and Nurr1 genes was not eosinophil-specific. Extremely intense apoptosis was induced in both eosinophils and an eosinophil cell line, AML14.3D10, by treatment with antibody (Ab) to both CD30 and Fas. Rapid expression of the genes for the NR4A receptor family was observed with anti-CD30 Ab treatment but not with anti-Fas Ab. The NR4A orphan nuclear receptor family gene expression and the subsequent eosinophil apoptosis were downregulated by the MAPK inhibitor, U0126. These results suggest that the expression of the NR4A receptor family genes through CD30 signaling may regulate eosinophil apoptosis in allergic conditions such as AD.

Developmental dissociation of T cells from B, NK, and myeloid cells revealed by MHC class II-specific chimeric immune receptors bearing TCR-zeta or FcR-gamma chain signaling domains

The T-cell receptor zeta (TCR-zeta) and FcR-gamma chains play a critical role in mediating signal transduction. We have previously described HIV glycoprotein 120 (gp120)-specific chimeric immune receptors (CIRs) in which the extracellular domain of CD4 is linked to the signaling domain of zeta (CD4zeta) or gamma (CD4gamma). Such CIRs are efficiently expressed following retroviral transduction of mature T cells and specifically redirect effector functions toward HIV-infected targets. In this report, we examine development of CD4zeta- or CD4gamma-expressing T cells from retrovirally transduced hematopoietic stem cells following bone marrow transplantation. Although CD4zeta/gamma-expressing myeloid, NK, and B cells were efficiently reconstituted, parallel development of CD4zeta/gamma-expressing T cells was blocked prior to the CD25(+)CD44(+) prothymocyte stage. In contrast, T cells expressing a signaling-defective CIR were efficiently generated. When major histocompatibility complex (MHC) class II-deficient mice were used as transplant recipients, development of CD4zeta/gamma-expressing T cells was restored. We conclude that CD4zeta/gamma signaling generated following engagement of MHC class II selectively arrests T-lineage development.

Induction of apoptosis by TPA and VP-16 is through translocation of TR3

AIM: To investigate the role of TR3 in induction of apoptosis in gastric cancer cells.

METHODS: Human gastric cancer cell line, MGC80-3, was used. Expression of TR3 mRNA and its protein was detected by Northern blot and Western blot. Localization of TR3 protein was showed by immunofluorescence analysis under laser-scanning confocal microscope. Apoptotic morphology was observed by DAPI fluorescence staining, and apoptotic index was counted among 1000 cells randomly. Stable transfection assay was carried out by Lipofectamine.

RESULTS: Treatment of MGC80-3 cells with TPA and VP-16 resulted in apoptosis, accompanied by the repression of Bcl-2 protein in a time-dependent manner. At the same time, TPA and VP-16 also up-regulated expression level of TR3 mRNA in MGC80-3 cells that expressed TR3 mRNA. When antisense-TR3 expression vector was transfected into the cells, expression of TR3 protein was repressed. In this case, TPA and VP-16 did not induce apoptosis. In addition, TPA and VP-16-induced apoptosis involved in translocation of TR3. In MGC80-3 cells, TR3 localized concentrative in nucleus, after treatment of cells with TPA and VP-16, TR3 translocated from nucleus to cytosol obviously. However, when this nuclear translocation was blocked by LMB, apoptosis was not occurred in MGC80-3 cells even in the presence of TPA and VP-16.

CONCLUSION: Induction of apoptosis by TPA and VP-16 is through induction of TR3 expression and translocation of TR3 from nucleus to cytosol, which may be a novel signal pathway for TR3, and represent the new biological function of TR3 to exert its effect on apoptosis in gastric cancer cells.

RRR-alpha-tocopheryl succinate inhibits human gastric cancer SGC-7901 cell growth by inducing apoptosis and DNA synthesis arrest

AIM

To investigate the effects of growth inhibition of human gastric cancer SGC-7901 cell with RRR-alpha-tocopheryl succinate (VES), a derivative of natural Vitamin E, via inducing apoptosis and DNA synthesis arrest.

METHODS

Human gastric cancer SGC-7901 cells were regularly incubated in the presence of VES at 5, 10 and 20mg x L(-1) (VES was dissolved in absolute ethanol and diluted in RPMI 1640 complete condition media correspondingly to a final concentration of VES and 1 mL x L(-1) ethanol), succinic acid and ethanol equivalents as vehicle (VEH) control and condition media only as untreated (UT) control. Trypan blue dye exclusion analysis and MTT assay were applied to detect the cell proliferation. Cells were pulsed with 37kBq of tritiated thymidine and (3H) TdR uptake was measured to observe DNA synthesis. Apoptotic morphology was observed by electron microscopy and DAPI staining. Flow cytometry and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay were performed to detect VES-triggered apoptosis.

RESULTS

VES inhibited SGC-7901 cell growth in a dose-dependent manner. The growth curve showed suppression by 24.7%, 49.2% and 68.7% following 24h of VES treatment at 5, 10 and 20 mg x L(-1), respectively, similar to the findings from MTT assay. DNA synthesis was evidently reduced by 35%, 45% and 98% after 24h VES treatment at 20mg x L(-1) and 48 h at 10 and 20mg x L(-1), respectively. VES induced SGC-7901 cells to undergo apoptosis with typically apoptotic characteristics, including morphological changes of chromatin condensation, chromatin crescent formation/margination, nucleus fragmentation and apoptotic body formation, typical apoptotic sub-G1 peak by flow cytometry and increase of apoptotic cells by TUNEL assay in which 90% of cells underwent apoptosis after 48 h of VES treatment at 20 mg x L(-1).

CONCLUSION

VES can inhibit human gastric cancer SGC-7901 cell growth by inducing apoptosis and DNA synthesis arrest. Inhibition of SGC-7901 cell growth by VES is dose- and time-dependent. Therefore VES can function as a potent chemotherapeutic agent against human gastric carcinogenesis.