Target cells for an immunosuppressive cytokine, glycosylation-inhibiting factor

Xenografting of human umbilical mesenchymal stem cells from Wharton's jelly ameliorates mouse spinocerebellar ataxia type 1

BACKGROUND

Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant neurodegenerative disorder caused by the expansion of CAG repeats in ATXN1 gene resulting in an expansion of polyglutamine repeats in the ATXN1 protein. Unfortunately, there has yet been any effective treatment so far for SCA1. This study investigated the feasibility of transplanting human umbilical mesenchymal stem cells (HUMSCs) into transgenic SCA1 mice containing an expanded uninterrupted allele with 82 repeats in the ATXN1-coding region.

METHODS

106 human umbilical mesenchymal stem cells were transplanted into the cerebella at 1 month of age.

RESULTS

HUMSCs displayed significant ameliorating effects in SCA1 mice in terms of motor behaviors in balance beam test and open field test as compared with the untransplanted SCA1 mice. HUMSCs transplantation effectively reduced the cerebellar atrophy, salvaged Purkinje cell death, and alleviated molecular layer shrinkage. Electrophysiological studies showed higher amplitudes of compound motor action potentials as indicated by increasing neuronal-muscular response strength to stimuli after stem cell transplantation. At 5 months after transplantation, HUMSCs scattering in the mice cerebella remained viable and secreted cytokines without differentiating into neuronal or glia cells.

CONCLUSIONS

Our findings provide hope for a new therapeutic direction for the treatment of SCA1.

Post-translational regulation of macrophage migration inhibitory factor: Basis for functional fine-tuning

Macrophage migration inhibitory factor (MIF) is a chemokine-like protein and an important mediator in the inflammatory response. Unlike most other pro-inflammatory cytokines, a number of cell types constitutively express MIF and secretion occurs from preformed stores. MIF is an evolutionarily conserved protein that shows a remarkable functional diversity, including specific binding to surface CD74 and chemokine receptors and the presence of two intrinsic tautomerase and oxidoreductase activities. Several studies have shown that MIF is subject to post-translational modification, particularly redox-dependent modification of the catalytic proline and cysteine residues. In this review, we summarize and discuss MIF post-translational modifications and their effects on the biological properties of this protein. We propose that the redox-sensitive residues in MIF will be modified at sites of inflammation and that this will add further depth to the functional diversity of this intriguing cytokine.

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MIF is a pro-inflammatory cytokine with tautomerase and oxidoreductase activity.

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MIF is susceptible to post-translational modifications, including redox modification.

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Oxidants and electrophiles generated at inflammatory sites can modify MIF.

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The biological consequences of redox modification need detailed characterization.

Hypoxia and glucocorticoid signaling converge to regulate macrophage migration inhibitory factor gene expression

OBJECTIVE

Macrophage migration inhibitory factor (MIF) is a proinflammatory mediator involved in the pathogenesis of rheumatoid arthritis. This study was undertaken to identify the MIF promoter elements responsible for regulating gene expression.

METHODS

Luciferase reporter gene assays were used to identify the MIF promoter sequence responsible for basal activity. Bioinformatic analysis was used to predict transcription factor binding sites, and electrophoretic mobility shift assay (EMSA) was used to demonstrate transcription factor binding. Chromatin immunoprecipitation (ChIP) was used to demonstrate transcription factor loading on the MIF promoter.

RESULTS

We identified the minimal promoter sequence required for basal MIF promoter activity that was also capable of conferring glucocorticoid-dependent inhibition in a T lymphocyte model cell line. Deletion studies and EMSA revealed 2 elements in the MIF promoter that were responsible for basal promoter activity. The 5' element binds CREB/activating transcription factor 1, and the 3' element is a functional hypoxia-responsive element binding hypoxia-inducible factor 1alpha. Further studies demonstrated that the cis elements are both required for glucocorticoid-dependent inhibition. ChIP demonstrated glucocorticoid-dependent recruitment of glucocorticoid receptor alpha to the MIF promoter in lymphocytes within 1 hour of treatment and a concomitant decrease in acetylated histone H3.

CONCLUSION

Our findings indicate that hypoxia and glucocorticoid signaling converge on a single element regulating MIF; this regulatory unit is a potential interacting node for microenvironment sensing of oxygen tension and glucocorticoid action in foci of inflammation.

CD4 cell-secreted, posttranslationally modified cytokine GIF suppresses Th2 responses by inhibiting the initiation of IL-4 production

T helper 2 (Th2) cells are critical to the induction of IgE antibody and allergic inflammation, but how the pathological pathways are controlled in nonallergic individuals remains unclear. Here we report that glycosylation-inhibiting factor (GIF) suppresses Th2 effector generation. GIF is a cytokine encoded by the same gene that codes for macrophage migration inhibitory factor (MIF). GIF-deficient mice demonstrated enhanced T-dependent antibody formation especially of IgE isotype and allergic airway inflammation with the generation of regulatory T cells unaffected. GIF-deficient macrophages and dendritic cells revealed normal responsiveness to toll-like receptor (TLR) ligands. GIF undergoes a unique posttranslational modification, cysteinylation. The modified GIF, mainly secreted by activated T cells derived from CD4(+)CD25(-) cells, inhibited IL-4 production by the same cells whereas the unmodified GIF showed no effect. Bone marrow chimera experiment demonstrated that T cell-derived GIF suppressed the generation of Th effectors that secrete IL-4. During the first 24 h of CD3/CD28 stimulation in vitro, GIF secreted from naïve CD4 cells acted on the same cells, maintained nuclear factor of activated T cells (NFAT)c2 in the nucleus, and repressed IL-4 mRNA levels. Thus, GIF represents a self-regulatory mechanism of Th2 cell generation from naïve CD4 cells, in which the posttranslational modification plays a crucial role.

Human macrophage migration inhibitory factor: a proven immunomodulatory cytokine?

Macrophage migration inhibitory factor (MIF) is a pro-inflammatory mediator with the ability to induce various immunomodulatory responses and override glucocorticoid-driven immunosuppression. Some of these functions have been linked to the unusual enzymatic properties of the protein, namely tautomerase and oxidoreductase activities. However, there are conflicting reports regarding the functional role of these enzymatic properties in normal physiological homeostasis and disease progression. Therefore, we have produced a highly pure, virtually endotoxin-free recombinant MIF preparation and fully characterized this using a variety of biochemical and biophysical approaches. The recombinant protein, with demonstrable enzymatic activity, was then used to systematically examine the biological activity of MIF. Surprisingly, treatment with MIF alone failed to induce cytokine expression, with the exception of IL-8. However, co-treatment of lipopolysaccharide (LPS) in conjunction with MIF produced synergistic secretion of tumor necrosis factor-alpha, interleukin (IL)-1, and IL-8 compared with LPS alone. The potentiating effect of MIF was seen at physiologically relevant concentrations. These data suggest that MIF has no conventional cytokine activity but, rather, acts to modulate and amplify the response to LPS.

GIF inhibits Th effector generation by acting on antigen-presenting B cells

Glycosylation-inhibiting factor (GIF) is a 13-kDa cytokine secreted from T cells. Administration of bioactive recombinant GIF inhibits IgG1 and IgE Ab responses in vivo. Treatment of B cells with the cytokine reduces the secretion of IgG1 and IgE induced by LPS and IL-4. To examine the effect on cognate T-B interaction, GIF was added to low-density B cells from MD4 transgenic (Tg) mice, which express B cell receptor specific for hen egg lysozyme (HEL). The B cells were subsequently pulsed with HEL-OVA conjugate and cultured with OVA-specific naive CD4 T cells from DO11.10 Tg mice. Treatment of Ag-presenting B cells with GIF reduced expansion and IL-2 secretion of naive T cells and rendered them hyporesponsive to antigenic restimulation, resulting in 50--95% reduction of IL-4 and IFN-gamma secretion upon restimulation with Ag. GIF dramatically inhibited Th effector generation when it was added to B cells before pulsing with HEL-OVA, whereas it showed little to no effect when added after B cells were pulsed with Ag. GIF was more effective when B cells from MD4 Tg mice were pulsed with HEL-OVA than when they were pulsed with OVA. This cytokine did not affect Th effector generation when B cells or irradiated splenocytes pulsed with OVA(323--339) peptide stimulated naive DO11.10 T cells. Confocal microscopy revealed that GIF inhibited internalization of HEL by B cells from MD4 Tg mice. Therefore, the cytokine may regulate early steps of Ag presentation involving B cell receptors to diminish Th effector generation from naive CD4 T cells.

Posttranslational modification of the glycosylation inhibiting factor (GIF) gene product generates bioactive GIF

Glycosylation inhibiting factor (GIF) and macrophage migration inhibitory factor (MIF) share an identical structure gene. Here we unravel two steps of posttranslational modifications in GIF/MIF molecules in human suppressor T (Ts) cell hybridomas. Peptide mapping and MS analysis of the affinity-purified GIF from the Ts cells revealed that one modification is cysteinylation at Cys-60, and the other is phosphorylation at Ser-91. Cysteinylated GIF, but not the wild-type GIF/MIF, possessed immunosuppressive effects on the in vitro IgE antibody response and had high affinity for GIF receptors on the T helper hybridoma cells. In vitro treatment of wild-type recombinant human GIF/MIF with cystine resulted in preferential cysteinylation of Cys-60 in the molecules. The cysteinylated recombinant human GIF and the Ts hybridoma-derived cysteinylated GIF were comparable both in the affinity for the receptors and in the immunosuppressive activity. Polyclonal antibodies specific for a stretch of the amino acid sequence in alpha2-helix of GIF bound bioactive cysteinylated GIF but failed to bind wild-type GIF/MIF. These results strongly suggest that cysteinylation of Cys-60 and consequent conformational changes in the GIF/MIF molecules are responsible for the generation of GIF bioactivity.

Presence of the 55 kDa glycosylation inhibiting factor in human serum

An ELISA system for the human glycosylation inhibiting factor (GIF) was established using polyclonal antibodies against highly purified 13 kDa recombinant human GIF, and the concentration of GIF in the sera of healthy donors and patients with various diseases was determined. GIF was detected in the sera of most healthy individuals and its concentration tended to increase with age. It was also found that the serum GIF levels markedly increased in some patients with rheumatoid arthritis or malignant tumors. Analysis of serum samples by SDS-PAGE and immunoblotting revealed a 55 kDa protein that has both the GIF antigenic determinant and the TCR alpha chain determinant. A 13 kDa GIF was not detected in the sera. In view of our previous findings on antigen-specific GIF from murine suppressor T cell hybridomas indicating that the 55 kDa GIF is a post-translationally formed conjugate of a TCR alpha chain with 13 kDa GIF, we suspect that the 55 kDa GIF detected in human sera is a human homologue of the murine 55 kDa GIF.