Cytokine-inducible protein SSI-1 [signal transducers and activators of transcription (STAT)-induced STAT inhibitor 1, also referred to as SOCS-1 (suppressor of cytokine signaling 1) or JAB (Janus kinase-binding protein)] negatively regulates cytokine receptor signaling by inhibition of JAK kinases. The SSI family of proteins includes eight members that are structurally characterized by an SH2 domain and a C-terminal conserved region that we have called the SC-motif. In this study, we investigated the roles of these domains in the function of SSI-1. Results of reporter assays demonstrated that the pre-SH2 domain (24 aa in front of the SH2 domain) and the SH2 domain of SSI-1 were required for the suppression by SSI-1 of interleukin 6 signaling. Coexpression studies of COS7 cells revealed that these domains also were required for inhibition of three JAKs (JAK1, JAK2, and TYK2). Furthermore, deletion of the SH2 domain, but not the pre-SH2 domain, resulted in loss of association of SSI-1 with TYK2. Thus, SSI-1 associates with JAK family kinase via its SH2 domain, and the pre-SH2 domain is required for the function of SSI-1. Deletion of the SC-motif markedly reduced expression of SSI-1 protein in M1 cells, and this reduction was reversed by treatment with proteasome inhibitors, suggesting that this motif is required to protect the SSI-1 molecule from proteolytic degradation. Based on these findings, we concluded that three distinct domains of SSI-1 (the pre-SH2 domain, the SH2 domain, and the SC-motif) cooperate in the suppression of interleukin 6 signaling.

Growth, differentiation, and programmed cell death (apoptosis) are mainly controlled by cytokines. The Janus kinase-signal transducers and activators of transcription (JAK-STAT) signal pathway is an important component of cytokine signaling. We have previously shown that STAT3 induces a molecule designated as SSI-1, which inhibits STAT3 functions. To clarify the physiological roles of SSI-1 in vivo, we generated, here, mice lacking SSI-1. These SSI-1؊͞؊ mice displayed growth retardation and died within 3 weeks after birth. Lymphocytes in the thymus and spleen of the SSI-1؊͞؊ mice exhibited accelerated apoptosis with aging, and their number was 20-25% of that in SSI-1؉͞؉ mice at 10 days of age. However, the differentiation of lymphocytes lacking SSI-1 appeared to be normal. Among various pro-and anti-apoptotic molecules examined, an up-regulation of Bax was found in lymphocytes of the spleen and thymus of SSI-1؊͞؊ mice. These findings suggest that SSI-1 prevents apoptosis by inhibiting the expression of Bax.The homeostatic regulation of cell populations is controlled by a balance among proliferation, growth arrest, and apoptosis, and this balance is mainly controlled by cytokines and growth factors. Cytokines act by binding to receptors expressed on the surfaces of responsive cells, which are associated with one or more members of the Janus kinase (JAK) family of cytoplasmic tyrosine kinases. The JAK-signal transducers and activators of transcription (STAT) signal pathway plays an important role in cytokine signaling (1-3), and is unique in that it features a direct linkage of receptor-ligand interaction on the cell surface to gene expression in the nucleus (4-6). However, the mechanism of negative control of cytokine actions involved in limiting their signal transductions is comparatively less well characterized. In 1997, the molecules that were expressed by stimulation of cytokine such as interleukin 6 (IL-6) and inhibited cytokine signal transmission by binding to JAK were isolated [STAT-induced STAT inhibitor-1 (SSI-1), suppressor of cytokine signaling (SOCS-1), Jak-binding protein (JAB)] (7-9). Subsequently, SSI-1 was found to form a family consisting of at least eight molecules, which were structurally characterized by an SH2 domain and a C-terminal conserved region (SC-motif͞SOCS-box͞CH-domain) (10-12), and it was recently known that SSI-1 inhibits not only IL-6 signaling but also interferon (IFN)-␥, IL-2, IL-3, and growth hormone signaling in vitro (13). It is expected that further study of SSI family molecules engaged in the negative feedback mechanism of cytokines will clarify the control mechanism of cytokines, which have remained obscure. MATERIALS AND METHODS Generation of SSI-1-Deficient Mice.A 129͞G mouse genomic library (Stratagene) containing the SSI-1 gene was screened, subcloned into the pBluescript vector, and characterized by restriction endonuclease mapping and DNA sequencing. A targeting vector was designed to replace the SSI-1 intron with phosphoglycerate kinase neo. This targeting...

Balloon pulmonary angioplasty (BPA) has been reported to improve haemodynamics and functional capacity, with an acceptable risk, in patients with chronic thromboembolic pulmonary hypertension (CTEPH) who are not candidates for pulmonary endarterectomy. However, right ventricular (RV) function, an important predictor in CTEPH, remains to be elucidated. We aimed to examine the impact of BPA on RV remodelling and dysfunction relative to haemodynamic improvements in patients with inoperable CTEPH.20 consecutive patients with inoperable CTEPH who underwent BPA with cardiovascular magnetic resonance before and after BPA were retrospectively studied.BPA led to significant amelioration of the mean pulmonary arterial pressure, cardiac index and pulmonary vascular resistance (PVR), without death or major complications. Furthermore, BPA significantly ameliorated right-sided heart failure symptoms and signs, and exercise capacity. Cardiovascular magnetic resonance revealed a marked improvement in RV end-diastolic and end-systolic volume index, with concomitant improvements in RV ejection fraction, mass and interventricular septal bowing after BPA. Changes in RV volumes strongly correlated with changes in cardiac index and PVR.BPA induced RV reverse remodelling and improved systolic dysfunction safely by ameliorating haemodynamics in patients with inoperable CTEPH. Evaluating RV function with cardiovascular magnetic resonance may be effective for noninvasively monitoring BPA efficacy. @ERSpublications BPA safely ameliorates haemodynamics, leading to right ventricular reverse remodelling in inoperable CTEPH

Suppressor of cytokine signaling-1 (SOCS-1), also known as STAT-induced STAT inhibitor-1 (SSI-1), is a negative feedback molecule for cytokine signaling, and its in vivo deletion induces fulminant hepatitis. However, elimination of the STAT1 or STAT6 gene or deletion of NKT cells substantially prevented severe hepatitis in SOCS-1-deficient mice, while administration of IFN-gamma and IL-4 accelerated its development. SOCS-1 deficiency not only sustained IFN-gamma/IL-4 signaling but also eliminated the cross-inhibitory action of IFN-gamma on IL-4 signaling. These results suggest that SOCS-1 deficiency-induced persistent activation of STAT1 and STAT6, which would be inhibited by SOCS-1 under normal conditions, may induce abnormal activation of NKT cells, thus leading to lethal pathological changes in SOCS-1-deficient mice.

Signal transducers and activators of transcription (STAT)-inducedSTAT inhibitor-1 [SSI-1; also known as suppressor of cytokine signaling-1 (SOCS-1)] was identified as a negative feedback regulator of Janus kinase-STAT signaling. We previously generated mice lacking the SSI-1 gene (SSI-1 ؊͞؊) and showed that thymocytes and splenocytes in SSI-1 ؊͞؊ mice underwent accelerated apoptosis. In this paper, we show that murine embryonic fibroblasts lacking the SSI-1 gene are more sensitive than their littermate controls to tumor necrosis factor-␣ (TNF-␣)-induced cell death. In addition, L929 cells forced to express SSI-1 (L929͞SSI-1), but not SSI-3 or SOCS-5, are resistant to TNF-␣-induced cell death. Furthermore L929͞SSI-1 cells treated with TNF-␣ sustain the activation of p38 mitogen-activated protein (MAP) kinase. In contrast, SSI-1 ؊͞؊ murine embryonic fibroblasts treated with TNF-␣ show hardly any activation of p38 MAP kinase. These findings suggest that SSI-1 suppresses TNF-␣-induced cell death, which is mediated by p38 MAP kinase signaling.

Signal transducer and activator of transcription (STAT)-induced STAT inhibitor 1 (SSI-1) is known to function as a negative feedback regulator of cytokine signaling, but it is unclear whether it is involved in other biological events. Here, we show that SSI-1 participates and plays an important role in the insulin signal transduction pathway. SSI-1–deficient mice showed a significantly low level of blood sugar. While the forced expression of SSI-1 reduced the phosphorylation level of insulin receptor substrate 1 (IRS-1), SSI-1 deficiency resulted in sustained phosphorylation of IRS-1 in response to insulin. Furthermore, SSI-1 achieves this inhibition both by binding directly to IRS-1 and by suppressing Janus kinases. These findings suggest that SSI-1 acts as a negative feedback factor also in the insulin signal transduction pathway through the suppression of IRS-1 phosphorylation.

STAT-induced STAT inhibitor-1 (SSI-1), also referred to as suppressor of cytokine signaling-1 and JAK-binding protein, is a member of a new family, the members of which are negative regulators of cytokine signals. SSI-1 is induced by various cytokines; however, the transcriptional mechanism of the SSI-1 gene is not fully understood. Here, we showed that transcription of the mouse SSI-1 gene was initiated from six adjoining sites accompanying three GC boxes and a single GC box-like element near them, but not from the TATA box or an initiator sequence. We also showed that IFN-γ induced SSI-1 mRNA more strongly than IL-6 in NIH-3T3 fibroblasts and that this IFN-γ effect was mediated by Stat1. To determine the signal pathway downstream of Stat1, transcriptional activities of several mutant promoters were examined. The region mediating stimulatory effect of IFN-γ to the gene transcription was localized to the −88/−60 region containing three tandem GAAA units, named variant IFN-γ-responsive element (VIRE), while four IFN-γ activation site (GAS)-like elements located far upstream were not related to the IFN-γ response. Gel-shift assays revealed that IFN-γ induced IFN regulatory factor-1 (IRF-1) binding to VIRE, but not that of IRF-2 or three components of ISGF3. Furthermore, forced expression of IRF-1 mimicked and that of IRF-2 inhibited the stimulatory effect of IFN-γ on SSI-1 gene transcription. Finally, mouse embryonal fibroblasts lacking IRF-1 showed impaired SSI-1 mRNA induction by IFN-γ. These results demonstrated that IRF-1, which is induced by activation of Stat1, mediated transcriptional activation of the SSI-1 gene by IFN-γ via VIRE.

Large-extent LGE correlates with absence of LV functional improvement and high incidence of adverse outcomes in patients with CS after steroid therapy.