Biomedical subjects

Masakiyo Nakahira

Publications and source records attributed to Masakiyo Nakahira.

6 recordsLinked to original sources

PubMed2026

PDLIM4 promotes dephosphorylation of STAT transcription factors by recruiting PTP-BL and inhibits Th1, Th2, and Th17 cell differentiation.

STAT (signal transducers and activators of transcription) transcription factors are activated by tyrosine phosphorylation after cytokine stimulation and are critical for the differentiation of T-helper (Th) cells into particular Th lineage subsets. How STAT-mediated Th cell differentiation is negatively regulated, however, is not fully understood. Here, we report that PDLIM4 binds to STAT3, 4, and 6 and suppresses gene activation mediated by these STATs. PDLIM4 acts as an adaptor that recruits PTP-BL, a protein tyrosine phosphatase, through its LIM (abnormal cell lineage 11-islet 1-mechanosensory abnormal 3) domain, facilitating dephosphorylation of STAT proteins. PDLIM4-deficiency in CD4+ T cells resulted in augmented tyrosine phosphorylation of these STAT proteins and consequently enhanced Th1, Th2, and Th17 cell differentiation, suggesting that PDLIM4 regulates the differentiation of multiple lineages of Th cells by suppressing STAT signaling. We further found that a non-synonymous single-nucleotide polymorphism in PDLIM4, which causes the substitution of a glycine residue with a cysteine in the LIM domain, is associated with susceptibility to rheumatoid arthritis and Graves' disease, both of which are known to be Th17 cell-driven autoimmune diseases. Notably, PDLIM4 containing this amino acid substitution in the LIM domain showed reduced binding to PTP-BL and was therefore partially impaired in its ability to dephosphorylate STAT3 and suppress STAT3 signaling. Our findings define an essential role of PDLIM4 in negatively regulating STAT-mediated Th-cell differentiation and preventing the onset of human autoimmune diseases.

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PubMed2004

A mechanism underlying STAT4-mediated up-regulation of IFN-gamma induction inTCR-triggered T cells.

IL-12 promotes T(h)1 development/IFN-gamma expression by activating STAT4. However, it is still unclear how STAT4 elicits IFN-gamma promoter activation. Here, we investigated the mechanism by which IL-12-activated STAT4 functions for IFN-gamma induction in TCR-triggered T cells. TCR stimulation induced high levels of IFN-gamma production depending on co-stimulation with IL-12. IL-12 stimulation greatly enhanced the promoter-binding activity of c-Jun/AP-1, a critical transcription factor for IFN-gamma gene expression in wild-type T cells, but not in STAT4-deficient (STAT4(-/-)) T cells. Comparable amounts of c-Jun were induced by TCR stimulation in both wild-type and STAT4(-/-) T cells irrespective of IL-12 co-stimulation. However, c-Jun bound to STAT4 in IL-12-co-stimulated wild-type T cells. c-Jun forming a complex with STAT4 efficiently interacted with the AP-1-related sequence of the IFN-gamma promoter. Such an enhanced c-Jun binding did not occur in STAT4(-/-) T cells. These results show that STAT4 contributes to enhancing IFN-gamma expression by up-regulating the binding of TCR signal-induced AP-1 to the relevant promoter sequence.

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PubMed2003

Differential requirements for JAK2 and TYK2 in T cell proliferation and IFN-gamma production induced by IL-12 alone or together with IL-18.

IL-12 activates TYK2 and Janus kinase (JAK)-2 to induce the phosphorylation of various signal transducers and activators of transcription (STAT) proteins. However, little is known regarding how these JAK exhibit the distinct biological effects of IL-12. Using two JAK inhibitors, tyrphostin A1 (A1) for TYK2 and tyrphostin B42 (B42) for JAK2, we investigated the involvement of JAK2 and TYK2 in IL-12-induced T cell proliferation and IFN-gamma production. B42, but not A1, inhibited T cell proliferation along with down-regulation of IL-12-induced c-Myc expression and STAT5 phosphorylation. In contrast, A1 but not B42 inhibited STAT4/STAT3 phosphorylation and IFN-gamma production. IL-18, but not IL-12, induced activator protein-1 (AP-1) responsible for high levels of IFN-gamma promoter activation. However, this IL-18 effect depended on the interaction of AP-1 with STAT4. A1 prevented AP-1 binding by inhibiting STAT4 involvement and down-regulated synergistic IFN-gamma promoter activation. These results indicate that JAK2 activation is required for IL-12-mediated T cell growth, whereas the TYK2-STAT4 signaling pathway is critical for IFN-gamma expression that is mediated by IL-12 alone and enhanced synergistically by combination with IL-18.

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PubMed2003

Tracking mouse visual pathways with WGA transgene.

By use of wheat germ agglutinin (WGA) cDNA as a transgene, we have succeeded in generating a transgenic mouse line in which the visual pathways can be accurately and reproducibly visualized. The WGA transgene was expressed in the retinal rod bipolar cells under the control of mouse L7 promoter. The transgene product, WGA protein, was transferred from the bipolar cells to the amacrine cells and the ganglion cells across synapses in the retinal neural circuitry and further conveyed along the optic nerve to the visual centers such as the suprachiasmatic nucleus, the lateral geniculate nucleus, the pretectal nucleus and the superior colliculus. By crossing the WGA-expressing transgenic mice with the retinal degeneration mutant mice, we analyzed change in the visual pathways by monitoring WGA immunoreactivity and found that the disorganization process of the visual pathways was relatively slow in spite of the rapid degeneration of the photoreceptor cells. Thus, this transgenic mouse line would provide a useful tool for analyzing phenotypic changes in the visual pathways of various mutant mice.

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PubMed2002

Molecular mechanisms underlying differential contribution of CD28 versus non-CD28 costimulatory molecules to IL-2 promoter activation.

T cell costimulation via CD28 and other (non-CD28) costimulatory molecules induces comparable levels of [(3)H]TdR incorporation, but fundamentally differs in the contribution to IL-2 production. In this study, we investigated the molecular basis underlying the difference between CD28 and non-CD28 costimulation for IL-2 gene expression. Resting T cells from a mutant mouse strain generated by replacing the IL-2 gene with a cDNA encoding green fluorescent protein were stimulated with a low dose of anti-CD3 plus anti-CD28 or anti-non-CD28 (CD5 or CD9) mAbs. CD28 and non-CD28 costimulation capable of inducing potent [(3)H]TdR uptake resulted in high and marginal levels of green fluorescent protein expression, respectively, indicating their differential IL-2 promoter activation. CD28 costimulation exhibited a time-dependent increase in the binding of transcription factors to the NF-AT and NF-kappaB binding sites and the CD28-responsive element of the IL-2 promoter, whereas non-CD28 costimulation did not. Particularly, a striking difference was observed for the binding of NF-kappaB to CD28-responsive element and the NF-kappaB binding site. Decreased NF-kappaB activation in non-CD28 costimulation resulted from the failure to translocate a critical NF-kappaB member, c-Rel, to the nuclear compartment due to the lack of IkappaBbeta inactivation. These observations suggest that unlike CD28 costimulation, non-CD28 costimulation fails to sustain IL-2 promoter activation and that such a failure is ascribed largely to the defect in the activation of c-Rel/NF-kappaB.

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PubMed2002

Synergy of IL-12 and IL-18 for IFN-gamma gene expression: IL-12-induced STAT4 contributes to IFN-gamma promoter activation by up-regulating the binding activity of IL-18-induced activator protein 1.

IL-12 and IL-18 synergistically enhance IFN-gamma mRNA transcription by activating STAT4 and AP-1, respectively. However, it is still unknown how STAT4/AP-1 elicit IFN-gamma promoter activation. Using an IL-12/IL-18-responsive T cell clone, we investigated the mechanisms underlying synergistic enhancement of IFN-gamma mRNA expression induced by these two cytokines. Synergy was observed in a reporter gene assay using an IFN-gamma promoter fragment that binds AP-1, but not STAT4. An increase in c-Jun, a component of AP-1, in the nuclear compartment was elicited by stimulation with either IL-12 or IL-18, but accumulation of serine-phosphorylated c-Jun was induced only by IL-18 capable of activating c-Jun N-terminal kinase. The binding of AP-1 to the relevant promoter sequence depended on the presence of STAT4. STAT4 bound with c-Jun, and a phosphorylated c-Jun-STAT4 complex most efficiently interacted with the AP-1-relevant promoter sequence. Enhanced cobinding of STAT4 and c-Jun to the AP-1 sequence was also observed when activated lymph node T cells were exposed to IL-12 plus IL-18. These results show that STAT4 up-regulates AP-1-mediated IFN-gamma promoter activation without directly binding to the promoter sequence, providing a mechanistic explanation for IL-12/IL-18-induced synergistic enhancement of IFN-gamma gene expression.

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