Anti-STAT1 Antibody [SM1] (A85870)

Stefin B (cystatin B) is an endogenous cysteine cathepsin inhibitor, and the loss-of-function mutations in the stefin B gene were reported in patients with Unverricht-Lundborg disease (EPM1). In this study we demonstrated that stefin B-deficient (StB KO) mice were significantly more sensitive to the lethal LPS-induced sepsis and secreted higher amounts of pro-inflammatory cytokines IL-1β and IL-18 in the serum. We further showed that increased caspase-11 gene expression and better pro-inflammatory caspase-1 and -11 activation determined in StB KO bone marrow-derived macrophages resulted in enhanced IL-1β processing. Pretreatment of macrophages with the cathepsin inhibitor E-64d did not affect secretion of IL-1β, suggesting that the increased cathepsin activity determined in StB KO bone marrow-derived macrophages is not essential for inflammasome activation. Upon LPS stimulation, stefin B was targeted into the mitochondria, and the lack of stefin B resulted in the increased destabilization of mitochondrial membrane potential and mitochondrial superoxide generation. Collectively, our study demonstrates that the LPS-induced sepsis in StB KO mice is dependent on caspase-11 and mitochondrial reactive oxygen species but is not associated with the lysosomal destabilization and increased cathepsin activity in the cytosol.

Suppressors of cytokine signaling (SOCS) are important regulators of lipopolysaccharide (LPS) and cytokine responses but their role in macrophage polarization is unknown. We have shown here that myeloid-restricted Socs3 deletion (Socs3(Lyz2cre)) resulted in resistance to LPS-induced endotoxic shock, whereas Socs2(-/-) mice were highly susceptible. We observed striking bias toward M2-like macrophages in Socs3(Lyz2cre) mice, whereas the M1-like population was enriched in Socs2(-/-) mice. Adoptive transfer experiments showed that responses to endotoxic shock and polymicrobial sepsis were transferable and macrophage dependent. Critically, this dichotomous response was associated with enhanced regulatory T (Treg) cell recruitment by Socs3(Lyz2cre) cells, whereas Treg cell recruitment was absent in the presence of Socs2(-/-) macrophages. In addition, altered polarization coincided with enhanced interferon-gamma (IFN-γ)-induced signal transducer and activator of transcription-1 (STAT1) activation in Socs2(-/-) macrophages and enhanced interleukin-4 (IL-4) plus IL-13-induced STAT6 phosphorylation in Socs3(Lyz2cre) macrophages. SOCS, therefore, are essential controllers of macrophage polarization, regulating inflammatory responses.

STAT 1, a member of latent cytoplasmic proteins, plays a pivotal role in mediating biological effects of interferons. Its transducing, DNA binding and transcriptional activity require phosphorylation at both Tyr 701 (Y 701) and Ser 727 (S 727) residues. Deficient phosphorylation or constitutive activation of the STAT 1 protein were observed in some human malignancies. Using immunoprecipitation and Western blots performed with lysates made of melanoma cells derived from patients with clinical stage II/III and employing specific anti-STAT 1 PS 727/PY 701 immunoprobes, we show that STAT 1 activation response induced by IFN-alpha/-gamma is significantly impaired. On average, three quarters of patients were lacking phosphorylation at S 727. STAT 1 PY 701 was not inducible by IFN-alpha in 63% and by IFN-gamma in 34% of samples. However, these STAT 1 activation defects showed no correlation with the disease outcome and immunotherapy response as indicated by progression-free survival profiles in patients treated with IFN-alpha2b.

STAT 1, a member of signal transducers and transcription activators of STAT family proteins, has been implicated as important mediator of IFN signaling. Functional activation of STAT 1 requires tyrosine and serine phosphorylation. Defects in its expression or activation in response to IFNs were observed in numerous pathological conditions including cancer. To further explore cancer-associated impaired STAT 1 response to IFNs, the inducibility of serine (S 727) and tyrosine (Y 701) phosphorylation by IFN-alpha/-gamma was assessed in 21 melanoma cell lines and in 35 primary cultures derived from melanoma patients. STAT 1 levels and inducibility of its activated phospho-forms were detected by Western analysis using specific polyclonal and monoclonal antibodies. All cell lines as well as patient melanoma samples expressed STAT 1 with variable signal intensity. Significant impaired IFN-induced STAT 1 S 727 phosphorylation was observed in both model systems with average of 77% of non-responders recorded in patient melanoma cells and 76% in melanoma cell lines. Failure of PY 701 induction occurred in patient samples (63% after IFN-alpha and 34% after IFN-gamma induction) and to a lesser degree in cell lines (i.e. response absence to IFN-alpha in 5 and to IFN-gamma in 2 melanoma lines). Our study demonstrates STAT 1 functional abnormalities in melanoma cells. On the basis of detailed analyses of patient melanoma cells with respect to the inducibility of STAT 1 phosphorylation by IFNs, four categories of patients could be distinguished: a) activation on both S 727 and Y 701, b) not inducible response, c) activation on Y 701 but not on S 727, d) heterogeneous response. Clinical study is now in progress to establish the significance of in vitro STAT 1 activation for predicting the response to IFN-based therapy and to explore biological consequences in cases responding in vitro to IFN-induced STAT 1 activation on only one of the critical amino acid residues.

BACKGROUND & AIMS:

Approximately half of hepatitis C virus (HCV)-infected patients do not respond to current interferon (IFN)-alpha combination therapy. To understand IFN-alpha resistance in vivo, we examined the dynamic responses to both type I and type II IFNs, human IFN (hIFN)-alpha, -gamma, and consensus IFN, in the chimpanzee model.

METHODS:

Naive and HCV-infected chimpanzees were treated with 3 forms of hIFNs in vivo. Quantitative real-time polymerase chain reaction was performed to evaluate the expression of IFN-stimulated genes (ISGs) in both peripheral blood mononuclear cells and liver to compare the responses to hIFN between naive and infected chimpanzees. The hepatic expression of IFN signaling components and inhibitory regulators including suppressor of cytokine signaling 3 (SOCS3) were assessed. SOCS3 expression was also evaluated in the liver of HCV-infected patients undergoing IFN treatment.

RESULTS:

The in vivo responses to all 3 hIFNs were much lower in the HCV-infected chimpanzees than those in the naive chimpanzees. This defect was particularly evident in the liver because induction of hepatic ISGs was barely detectable in the infected animals. Following IFN administration, the expression of SOCS3 was significantly up-regulated, possibly through induction of interleukin-6, in the liver of HCV-infected chimpanzees. HCV-infected humans also showed a differential pattern of hepatic SOCS3 expression in response to IFN that is associated with treatment response.

CONCLUSIONS:

Our data indicate a predominantly defective hepatic response to IFN in HCV-infected chimpanzees, which is probably mediated through the activation of SOCS3 and may explain the nonresponse of many HCV patients to IFN-based therapy.