STAT3-mediated constitutive expression of SOCS-3 in cutaneous T-cell lymphoma

Reduced liver injury in the interleukin-6 knockout mice by chronic carbon tetrachloride administration

BACKGROUND

Interleukin-6 has been involved in restoration of liver function after partial hepatectomy and toxic liver injury. However, normal liver regeneration in interleukin-6 knockout mice has also been reported. The aim of this work was to investigate the effect of interleukin-6 deficiency on liver injury and its regeneration in a model of long term carbon tetrachloride (CCl4) administration.

DESIGN

Serum and whole livers from wild type and interleukin-6 knockout mice treated with carbon tetrachloride (0.25 mL kg(-1)) twice a week were obtained after 4, 6 and 8 weeks (n = 4-6). Sections were assessed for liver regeneration, liver injury and hepatocyte apoptosis whereas sera were assayed for aminotransferase levels. Nuclear extracts and total liver lysates were assayed for transcription factor activation and apoptosis related proteins, respectively.

RESULTS

When compared to wild type, interleukin-6 knockout mice showed reduced liver damage scores, lower aminotransferase levels and diminished apoptosis, as well as reduced nuclear factor kappa B activation. Although the level of active protein was lower, activation of signal transducer and activator of transcription 3 still takes place in knockout mice. Furthermore, liver regeneration measured by bromodeoxyuridine incorporation showed no differences between wild type and knockout animals after 6 and 8 weeks of treatment.

CONCLUSIONS

Compared to the wild type mice liver regeneration after chronic treatment with carbon tetrachloride proceeds at a slower rate in interleukin-6 deficient mice. However, this low recovery rate is accompanied by a reduction not only in hepatocyte apoptosis, but also in activation of nuclear factor kappa B and liver injury.

Cross-inhibition of interferon-induced signals by GM-CSF through a block in Stat1 activation

We investigated the effects of granulocyte-macrophage colony-stimulating factor (GM-CSF) on biologic signals induced by interferon-alpha (IFN-alpha) and IFN-gamma. In hematopoietic cell lines, IFN-induced signaling was investigated by Western blotting, electrophoretic mobility shift assays (EMSA), flow cytometry, protein-tyrosine phosphatase (PTP) assays, and RT-PCR. GM-CSF inhibited IFN-alpha-induced and IFN-gamma-induced Stat1 tyrosine phosphorylation in a time-dependent manner. EMSA showed that GM-CSF inhibited IFN-alpha-induced and IFN-gamma-induced IFN-gamma activator sequence (GAS) binding activity. As a consequence, IFN-induced transcription of the early response gene, IFN-stimulated gene 54 (ISG54), was inhibited. The expression of IFN regulatory factor-1 (IRF-1) and MHC class I antigens was downregulated at protein levels in hematopoietic cell lines (U937, THP1). In contrast to GM-CSF, granulocyte colony-stimulating factor (G-CSF) and interleukin-3 (IL-3) did not influence the IFN-induced Stat1 activation. To explore the molecular mechanism of suppression of Stat1 tyrosine phosphorylation, we investigated the induction and activation of cytokine-inducible SH2-containing protein/suppressor of cytokine signaling (CIS/SOCS) molecules and phosphatases on GM-CSF treatment. In contrast to G-CSF and IL-3, GM-CSF strongly induced the expression of CIS1 and SOCS2 at mRNA levels, but overexpression of CIS1 or SOCS2 in HEK293 cells did not show inhibition of Stat1 tyrosine phosphorylation upon IFN treatment. In PTP assays, on GM-CSF incubation, no enhanced src homology 2 domain tyrosine phosphatase 1 and 2 (SHP1 and SHP2) activity was detectable. However, GM-CSF-induced downregulation of Tyk2 and Jak1 tyrosine phosphorylation as well as Tyk2 protein levels likely contributed to the reduced Stat1 tyrosine phosphorylation. In hematopoietic cells, GM-CSF antagonizes IFN-induced signals by a block in Stat1 activation.

Transcriptional activation of the suppressor of cytokine signaling-3 (SOCS-3) gene via STAT3 is increased in F9 REX1 (ZFP-42) knockout teratocarcinoma stem cells relative to wild-type cells

Rex1 (Zfp42), first identified as a gene that is transcriptionally repressed by retinoic acid (RA), encodes a zinc finger transcription factor expressed at high levels in F9 teratocarcinoma stem cells, embryonic stem cells, and other stem cells. Loss of both alleles of Rex1 by homologous recombination alters the RA-induced differentiation of F9 cells, a model of pluripotent embryonic stem cells. We identified Suppressor of Cytokine Signaling-3 (SOCS-3) as a gene that exhibits greatly increased transcriptional activation in RA, cAMP, and theophylline (RACT)-treated F9 Rex1(-/-) cells (approximately 25-fold) as compared to wild-type (WT) cells ( approximately 2.5-fold). By promoter deletion, mutation, and transient transfection analyses, we have shown that this transcriptional increase is mediated by the STAT3 DNA-binding elements located between -99 to -60 in the SOCS-3 promoter. Overexpression of STAT3 dominant-negative mutants greatly diminishes this SOCS-3 transcriptional increase in F9 Rex1(-/-) cells. This increase in SOCS-3 transcription is associated with a four- to fivefold higher level of tyrosine-phosphorylated STAT3 in the RACT-treated F9 Rex1(-/-) cells as compared to WT. Dominant-negative Src tyrosine kinase, Jak2, and protein kinase A partially reduce the transcriptional activation of the SOCS 3 gene in RACT-treated F9 Rex1 null cells. In contrast, parathyroid hormone peptide enhances the effect of RA in F9 Rex1(-/-) cells, but not in F9 WT. Thus, Rex1, which is highly expressed in stem cells, inhibits signaling via the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway, thereby modulating the differentiation of F9 cells.

Reciprocal regulation of SOCS 1 and SOCS3 enhances resistance to ionizing radiation in glioblastoma multiforme

PURPOSE

The expression of suppressors of cytokine signaling 1 (SOCS1) and SOCS3 genes is dysregulated in several solid tumors, causing aberrant activation of cell growth and survival signaling pathways. In this study, we analyzed SOCS1 and SOCS3 gene expression in glioblastoma multiforme (GBM) and studied the role of each protein in GBM cell signaling and radiation resistance.

EXPERIMENTAL DESIGN

SOCS1 and SOCS3 gene expression was analyzed in 10 GBM cell lines by reverse transcription-PCR and Western blotting. SOCS3 expression was also studied in 12 primary GBM tissues by immunohistochemistry. The methylation status of the SOCS1 and SOCS3 loci was determined by methylation-specific PCR. Extracellular signal-regulated kinase (ERK)-mitogen-activated protein kinase (MAPK) activation in GBM cell lines overexpressing SOCS1 or lacking SOCS3 was determined by phosphorylated-specific Western blotting. Radiation responses in SOCS1-positive and SOCS3-deficient GBM cell lines and fibroblasts from wild-type and SOCS1 or SOCS3 knockout mice were studied in a clonogenic survival assay.

RESULTS

All GBM cell lines tested lacked SOCS1 expression, whereas GBM cell lines and primary GBM tumor samples constitutively expressed SOCS3. SOCS1 gene repression was linked to hypermethylation of the SOCS1 genetic locus in GBM cells. Reintroduction of SOCS1 or blocking SOCS3 expression sensitized cells to radiation and decreased the levels of activated ERK MAPKs in GBM cells.

CONCLUSIONS

SOCS1 and SOCS3 are aberrantly expressed in GBM cell lines and primary tissues. Altered SOCS gene expression leads to increased cell signaling through the ERK-MAPK pathway and may play a role in disease pathogenesis by enhancing GBM radioresistance.

STAT3Polymorphism Predicts Interferon-Alfa Response in Patients With Metastatic Renal Cell Carcinoma

Purpose

To clarify the effect of genetic polymorphisms on the response to interferon alfa (IFN-α) for metastatic renal cell carcinoma (MRCC), and to find a reliable molecular marker to select those patients with MRCC who would benefit from IFN-α immunotherapy.

Patients and Methods

We carried out an association study in which 463 single nucleotide polymorphisms (SNPs) in 33 candidate genes were genotyped in 75 Japanese patients who had received IFN-α for MRCC.

Results

After adjusting for lung metastasis, stepwise logistic regression analysis revealed that the SNPs in signal transducer and activator 3 (STAT3) were most significantly associated with better response to IFN-α. Linkage disequilibrium mapping revealed that the SNP in the 5′ region of STAT3, rs4796793, was the most significant predictor of IFN-α response (odds ratio [OR] = 2.73; 95% CI, 1.38 to 5.78). The highest OR was shown in the CC genotype at rs4796793 compared to the GG + GC genotypes (OR = 8.38, 95% CI, 1.63 to 42.96). Genotype-dependent expressions of STAT3 in B lymphocyte cell lines and the enhanced growth inhibitory effects of IFN-α by STAT3 suppression in an RCC cell line supported the results of the present association study.

Conclusion

The present study suggested that the STAT3 polymorphism is a useful diagnostic marker to predict the response to IFN-α therapy in patients with MRCC. An efficient response marker for IFN-α needs to be utilized to establish individual optimal treatment strategies, even when newer drug therapies are used as first line treatments for MRCC.

Clinical significance of mucosal suppressors of cytokine signaling 3 expression in ulcerative colitis

AIM: To investigate the clinical significance of mucosal expression of suppressors of cytokine signaling 1 (SOCS1) and SOCS3 in human ulcerative colitis (UC).

METHODS: Biopsy specimens for histological analysis and mRNA detection were obtained endoscopically from the rectum of 62 patients with UC (36 men; age 13-76 years). The patients were classified endoscopically according to Matts’ grade (grade 1 to 4). Expression of SOCS1 and SOCS3 mRNAs was quantified in samples by competitive reverse transcription-polymerase chain reaction (RT-PCR). GAPDH was used as an internal control for efficiency of RT-PCR and amount of RNA.

RESULTS: SOCS3 mRNA expression was significantly higher in inflamed mucosa of UC than in inactive mucosa. The level of expression was well correlated with the degree of both endoscopic and histologic inflammation. Interestingly, among the patients in remission, the group with relatively low expression of SOCS3 showed a higher rate of remission maintenance over a 12-mo period. In contrast, SOCS1 mRNA was expressed in both inflamed and non-inflamed colonic mucosa and was not correlated with the activity of colonic mucosa or prognosis.

CONCLUSION: These observations suggest that increased expression of mucosal SOCS3, but not of SOCS1, may play a critical role in the development of the colonic inflammation of UC.

IFN-alpha-induced signal transduction, gene expression, and antitumor activity of immune effector cells are negatively regulated by suppressor of cytokine signaling proteins

Proteins belonging to the suppressors of cytokine signaling (SOCS) family have been shown to regulate cytokine signal transduction in various cell types but their role in modulating the response of immune cells to IFN-alpha has not been fully explored. We hypothesized that SOCS proteins would inhibit the antitumor activity of IFN-alpha-stimulated immune cells. Transcripts for SOCS1, SOCS2, SOCS3, and cytokine-inducible Src homology 2-containing protein were identified in total human PBMC (PBMCs, NK cells, and T cells) within 1-2 h of stimulation with IFN-alpha (10(3)-10(5) U/ml). Immunoblot analysis confirmed the expression of these factors at the protein level. Transcripts for SOCS proteins were rapidly but variably induced in PBMCs from patients with metastatic melanoma following the i.v. administration of IFN-alpha-2b (20 million units/m(2)). Overexpression of SOCS1 and SOCS3, but not SOCS2, in the Jurkat T cell line inhibited IFN-alpha-induced phosphorylated STAT1 and the transcription of IFN-stimulated genes. Conversely, small inhibitory RNA-mediated down-regulation of SOCS1 and SOCS3 in Jurkat cells and normal T cells enhanced the transcriptional response to IFN-alpha. Loss of SOCS1 or SOCS3 in murine immune effectors was associated with enhanced IFN-induced phosphorylated STAT1, transcription of IFN-stimulated genes, and antitumor activity. Of note, IFN-alpha treatment eliminated melanoma tumors in 70% of SOCS1-deficient mice, whereas IFN-treated SOCS-competent mice all died. The antitumor effects of IFN-alpha in tumor-bearing SOCS1-deficient mice were markedly inhibited following depletion of CD8(+) T cells. These results indicate that the antitumor response of immune effector cells to exogenous IFN-alpha is regulated by SOCS proteins.

Constitutive Suppressor of Cytokine Signaling 3 Expression Confers a Growth Advantage to a Human Melanoma Cell Line

The growth of melanocytes and many early stage melanoma cells can be inhibited by cytokines, whereas late stage melanoma cells have often been reported to be "multi-cytokine-resistant." Here, we analyzed the melanoma cell line 1286, resistant towards the growth-inhibitory effects of interleukin 6 (IL-6), and oncostatin M (OSM), to better understand the mechanisms underlying cytokine resistance. Although the relevant receptors gp130 and OSMR are expressed at the cell surface of these cells, cytokine stimulation hardly led to the activation of Janus kinase 1 and signal transducer and activator of transcription (STAT)3 and STAT1. We found a high-level constitutive expression of suppressors of cytokine signaling 3 (SOCS3) that did not further increase after cytokine treatment. Importantly, upon suppression of SOCS3 by short interfering RNA, cells became susceptible towards OSM and IL-6: they showed an enhanced STAT3 phosphorylation and a dramatically increased STAT1 phosphorylation. Moreover, suppression of SOCS3 rendered 1286 cells sensitive to the antiproliferative action of IL-6 and OSM, but not of IFN-alpha. Interestingly, SOCS3-short interfering RNA treatment also increased the growth-inhibitory effect in cytokine-sensitive WM239 cells expressing SOCS3 in an inducible way. Thus, SOCS3 expression confers a growth advantage to these cell lines. Constitutive SOCS3 mRNA expression, although at lower levels than in 1286 cells, was found in nine additional human melanoma cell lines and in normal human melanocytes, although at the protein level, SOCS3 expression was marginal at best. However, in situ analysis of human melanoma specimens revealed SOCS3 immunoreactivity in 3 out of 10 samples, suggesting that in vivo SOCS3 may possibly play a role in IL-6 resistance in at least a fraction of tumors.

STAT3 as a therapeutic target in head and neck cancer

The signal transducer and activator of transcription (STAT) proteins relay signals from cytokine receptors and receptor tyrosine kinases on the cell surface to the nucleus, where they affect the transcription of genes involved in normal cell functions, including growth, apoptosis and differentiation. STAT3 has been found to be constitutively active in head and neck squamous cell carcinoma (HNSCC) as well as in other epithelial malignancies. In HNSCC, STAT3 alters the cell cycle, prevents apoptosis, and mediates the proliferation and survival of tumour cells. Several therapeutic approaches are being developed to target STAT3, including molecules that block either dimerisation or DNA binding by STAT3, strategies to decrease STAT3 expression and drugs that inhibit STAT3 function. Strategies that block STAT3 may prove efficacious for cancer treatment.

Lack of suppressive CD4+CD25+FOXP3+ T cells in advanced stages of primary cutaneous T-cell lymphoma

Mycosis fungoides and its leukemic variant, Sezary syndrome, are the most common primary cutaneous T-cell lymphomas (CTCLs). In an ex vivo study, we investigated the percentage, phenotype, and suppressive function of CD4+CD25+ regulatory T cells (Tregs) from peripheral blood of CTCL patients. The percentage of Tregs did not differ significantly between patients and controls. Functional assays demonstrated a dichotomy in Treg function: in four out of 10 patients CD4+CD25+ T cells were incapable of suppressing autologous CD4+CD25- T-cell proliferation, whereas suppressive function was intact in the other six patients. Suppressive activity of Tregs inversely correlated with the peripheral blood tumor burden. T-plastin gene expression, used as a Sezary cell marker, confirmed that Sezary cells were heterogeneous for CD25 expression. Mixed lymphocyte reactions demonstrated that CD4+CD25- T cells from patients who lacked functional Tregs were susceptible to suppression by Tregs from healthy controls, and had not become suppressive themselves. Furthermore, we found reduced expression of Foxp3 in the CD4+CD25+ Tregs of these patients relative to the other six CTCL patients and controls. Our findings thus indicate a dysfunction of peripheral Tregs in certain CTCL patients, which correlates with tumor burden.

Selective regulatory function of Socs3 in the formation of IL-17-secreting T cells

Suppressor of cytokine signaling (Socs) 3 is a cytokine-inducible inhibitor with critical but selective cell-specific effects. We show that deficiency of Socs3 in T cells had minimal effects on differentiation of T cells to the T helper (Th) 1 or Th2 subsets; accordingly, Socs3 had no effect on IL-12-dependent signal transducer and activator of transcription (Stat) 4 phosphorylation or IL-4-dependent Stat6 phosphorylation. By contrast, Socs3 was found to be a major regulator of IL-23-mediated Stat3 phosphorylation and Th17 generation, and Stat3 directly binds to the IL-17A and IL-17F promoters. We conclude that Socs3 is an essential negative regulator of IL-23 signaling, inhibition of which constrains the generation of Th17 differentiation.

Induction of SOCS-3 is insufficient to confer IRS-1 protein degradation in 3T3-L1 adipocytes

Insulin receptor substrate (IRS)-1 is a key protein in insulin signaling. Several studies have shown that the expression of IRS-1 can be modulated by protein degradation via the proteasome and the degradation of IRS-1 can be related to insulin-resistant states. The degradation of IRS-1 has been shown to be induced by SOCS-1 and SOCS-3 via the ubiquitin pathway. The goal of our study was to determine if the induction of SOCS-3 correlated with increased IRS-1 degradation in cultured 3T3-L1 adipocytes. Interestingly, our studies have shown that there is little correlation between the induction in SOCS-3 expression and the degradation of IRS-1 in mature 3T3-L1 adipocytes. Our results clearly demonstrate that treatment with leukemia inhibitory factor (LIF) or cardiotrophin (CT)-1 strongly induces the expression of SOCS-3 in mature 3T3-L1 adipocytes, but does not affect the degradation of IRS-1. On the contrary, tumor necrosis factor (TNF) alpha and insulin, which very weakly induce SOCS-3 expression, have profound effects on IRS-1 degradation. In summary, our results indicate that the expression of SOCS-3 does not correlate with the degradation of IRS-1 proteins in fat cells.

Increased expression of CTLA-4 in malignant T-cells from patients with mycosis fungoides -- cutaneous T cell lymphoma

Mycosis fungoides (MF) is a low-grade lymphoma of cluster of differentiation (CD)4+, CD45RO+, cutaneous leukocyte antigen (CLA)+ T cells that homes to the skin. To understand the functional abnormalities in this disease, we study the regulation of cytotoxic T-lymphocyte antigen (CTLA)-4 in peripheral blood mononuclear cells (PBMCs) from patients with MF. CTLA-4 is a costimulatory molecule for T cells that functions in immunoregulation. Unlike the expression of CD28, which is expressed constitutively on T cells, CTLA-4 expression is highly regulated. In the analysis of PBMCs in MF, we found that CTLA-4 is stimulated by phorbol myristate acetate/A23187 to a greater level when compared to normals. This defect was seen in the dominant clones of T cells. The increased CTLA-4 expression was significant between normal and MF, with a correlation between higher expression of CTLA-4 and a higher grade of MF. In a patient whose disease progressed, the CTLA-4 level increased. The abnormal level of CTLA-4 was confirmed at both the transcription and translation levels. Although MF is associated with a Th2 bias, Th1 cytokines IL-2 and IFN-gamma enhanced CTLA-4 expression, while IL-4 did not. These findings reveal an abnormal regulation of CTLA-4 expression in MF and show that PBMCs from patients with MF have properties that are divergent from those of normal T cells.

Suppression of IL-6 production and proliferation by blocking STAT3 activation in malignant soft tissue tumor cells

There is no established optimum treatment for malignant fibrous histiocytoma (MFH) at present, and few MFH cell lines are established. In the present study, we established new MFH cell lines, KHZ-MFH and SFT85-03, and investigated the JAK/STAT (Janus kinase/signal transducer and activator of transcription) signaling pathway. We found that MFH cells secreted high levels of IL-6 and that STAT3 was constitutively activated in these cells. The JAK2 kinase inhibitor, tyrphostin AG490, suppressed the growth of MFH cells and inhibited the secretion of IL-6. Furthermore, blockade of activated STAT3 by forced expression of a cytokine signaling repressor, SOCS3 gene as well as a dominant-negative STAT3 in these cells significantly suppressed their growth. These results indicated that an autocrine mechanism of the JAK/STAT3 signaling pathway could promote the growth of MFH cells and that this pathway could be a therapeutic target of MFH.

Induction of suppressor of cytokine signaling-3 by herpes simplex virus type 1 confers efficient viral replication

We showed previously that infection of herpes simplex virus type 1 (HSV-1) rapidly induced the suppressor of cytokine signaling-3 (SOCS3), a host negative regulator of the JAK/STAT pathway, in the amnion cell line FL. Thus, HSV-1 suppresses the interferon (IFN) signaling pathway at the step of IFN-induced phosphorylation of janus kinases during an early infection stage. In the present study, we examined SOCS3 induction by HSV-1 infection in several types of human cell lines. FL cells and the T-cell line CCRF-CEM strongly induced SOCS3 during HSV-1 infection. The virus rapidly propagated in both cell lines and produced a lytic infection. On the other hand, the monocytic cell lines U937 and THP-1, and the B-cell line AKATA showed neither SOCS3 induction nor suppression of IFN-induced STAT1 phosphorylation during HSV-1 infection. These cell lines resulted in a persistent or prolonged infection, which continuously produced a low titer of infectious virus. The induction of SOCS3 by HSV-1 should occur via STAT3 activation immediately after HSV-1 infection. SOCS3 induction was inhibited by the addition of a Jak3 inhibitor WHI-P131. Treatment with WHI-P131 or transfection of antisense oligonucleotides specific for SOCS3 dramatically suppressed replication of HSV-1 in FL cells. The suppression of viral replication by WHI-P131 was released in the presence of neutralizing anti-IFN-alpha and anti-IFN-beta antibodies. In conclusion, suppression of IFN signaling by HSV-1-induced SOCS3 is required for efficient replication and lytic infection of HSV-1. The SOCS3 induction varied among cell lines, indicating that it is an important factor determining the cell type specificity of efficient HSV-1 replication.

SOCS3 was induced by hypoxia and suppressed STAT3 phosphorylation in pulmonary arterial smooth muscle cells

Recently identified suppressors of cytokine signaling (SOCS) have been proposed as negative regulators of cytokine signaling, which have distinct mechanisms of inhibiting JAK-STAT pathway. In this study, using cultures of rat primary pulmonary vascular smooth muscle cells (PASMC), we found that hypoxia induced strongly STAT3 phosphorylation by up to four-fold. At the same time, mRNA for the endogenous cytokine signaling repressor SOCS3, but not SOCS1, was markedly induced in PASMC as early as 2h following hypoxic stimulation. Furthermore, forced expression of SOCS3 gene suppressed tyrosine phosphorylation of STAT3 and transcription of c-myc gene by more than 70% and 60% in PASMC under hypoxic conditions, respectively. Additionally, we showed here that hypoxia enhanced nearly two-fold increase of PASMC proliferation and overexpression of SOCS3 gene downregulated hypoxia-induced PASMC proliferation by about 50%. The finding suggest that STAT3-dependent pathway is involved in the activation and proliferation of PASMC stimulated by hypoxia, and SOCS3 is a rapidly hypoxia-inducible gene and acts to inhibit activation of cellular signaling pathway in a classical negative feedback loop.

Interleukin-6 and new strategies for the treatment of cancer, hyperproliferative diseases and paraneoplastic syndromes

Interleukin-6 (IL-6) is a pleiomorphic cytokine whose growth factor properties play an important role in the development and progression of many types of cancer. IL-6 is produced in response to a variety of stimuli, and is required for the development of T and B lymphocytes to effector cells. In certain neoplasias, such as multiple myeloma, IL-6 is both produced and required for survival by the cancer cell itself. In other neoplasias, IL-6 may come from tissue surrounding the tumour. Thus, therapeutic strategies aimed at inhibiting the production, expression or action of IL-6 would be quite beneficial in the treatment of cancer. Moreover, IL-6 is a pathophysiological factor in several hyperproliferative diseases and the paraneoplastic syndromes that often accompany cancer, such as cachexia and osteoporosis; thus, anti-IL-6 therapy would be useful in treating these entities as well. This expert opinion acquaints the reader with IL-6, its physiological responses, the cancer types with which it is associated, and discusses the current state of therapy aimed at inhibiting it.

Signal transducer and activator of transcription (STAT) signalling and T-cell lymphomas

Interaction of cytokines with their cognate receptors leads to the activation of latent transcription factors - the signal transducers and activators of transcription (STAT) proteins - whose biological activities ultimately regulate many critical aspects of cell growth, survival and differentiation. Dysregulation of the JAK-STAT pathway is frequently observed in many primary human tumours, reflecting the importance of this pathway in the maintenance of cellular integrity. Here we review the current progress in STAT structure and function, and the contribution of STAT signalling to the pathogenesis of T-cell lymphomas.

Sle1ab Mediates the Aberrant Activation of STAT3 and Ras-ERK Signaling Pathways in B Lymphocytes

The Sle1ab genomic interval on murine chromosome 1 mediates the loss of immune tolerance to chromatin resulting in antinuclear Abs (ANA) production in the lupus-prone NZM2410 mouse. Global gene expression analysis was used to identify the molecular pathways that are dysregulated at the initiation of B lymphocyte autoimmunity in B6.Sle1ab mice. This analysis identified that STAT3 and ras-ERK signaling pathways are aberrantly activated in Sle1ab B lymphocytes, consistent with increased production of IL-6 by splenic B lymphocytes and monocytes in B6.Sle1ab mice. In vitro treatment of splenic mononuclear cells isolated from ANA-positive Sle1ab mice with anti-IL-6 Ab or AG490, an inhibitor of STAT3 signaling pathway, suppressed ANA production in short-term culture, indicating that this pathway was essential to the production of autoantibodies. In vivo treatment of ANA-positive B6.Sle1ab mice with the ras pathway inhibitor, perillyl alcohol, suppressed the increase of ANA. These findings identify IL-6 as a early key cytokine in Sle1ab-mediated disease development and indicate that the STAT3 and ras-ERK signaling pathways are potential therapeutic targets for treating systemic lupus erythematosus.

Constitutive SOCS-3 expression protects T-cell lymphoma against growth inhibition by IFNα

Signal transducer and activator of transcription (Stat)3 is constitutively activated in cutaneous T-cell lymphoma (CTCL), where it protects tumour cells against apoptosis. The constitutive activation of Stat3 leads to a constitutive expression of suppressor of cytokine signalling (SOCS)-3. In healthy cells, SOCS-3 is transiently expressed following cytokine stimulation and functions as a negative feedback inhibitor of the Stat3-activating kinases. Here, we attempt to resolve the apparent paradox of a simultaneous SOCS-3 expression and Stat3 activation in the same cells. We show that (i) SOCS-3 expression in tumour cells is equal to or higher than in cytokine-stimulated nonmalignant T cells, (ii) SOCS-3 is not mutated in CTCL, (iii) overexpression of SOCS-3 blocks IFNalpha-mediated growth inhibition without affecting Stat3 activation, growth, and apoptosis, and (iv) inhibition of SOCS-3 by a dominant negative Stat3 (Stat3D) increases the IFNalpha-mediated growth inhibition. Taken together, these data show that SOCS-3 does not inhibit Stat3 activation, growth, and survival in CTCL. In contrast, SOCS3 protects tumour cells against growth inhibition by IFNalpha. Unlike SOCS-1, SOCS-3 is therefore not a tumour suppressor but rather a protector of tumour cells.

Differential hypermethylation of SOCS genes in ovarian and breast carcinomas

Suppressor of cytokine signaling (SOCS) proteins have emerged as critical attenuators of cytokine-mediated processes, suggesting a role in the suppression of tumorigenesis. In the ovary and mammary gland, cytokines such as prolactin and IL-6 are important regulators of growth and differentiation. We have investigated whether silencing or inactivation of SOCS genes occurs in ovarian and breast carcinomas. The SOCS1 and SOCS2 CpG islands were found to be hypermethylated in 23 and 14% of primary ovarian cancers, respectively, whereas only SOCS1 was methylated in breast cancers (9%). Methylation of these genes did not occur in normal tissues. No correlation was apparent between methylation and loss of heterozygosity, and no somatic mutations were found in a large panel of carcinomas. Aberrant methylation of these SOCS genes correlated with transcriptional silencing in ovarian and breast cancer cell lines, since expression was induced by the demethylating agent 5-azadeoxycytidine. SOCS3 was not hypermethylated in either cancer type. Consistent with this data, SOCS1 and SOCS2 but not SOCS3 suppressed the growth of ovarian and breast cancer cells. Hypermethylation and silencing of specific SOCS genes in the ovary, and to a lesser extent in breast, may augment cytokine responsiveness in these tissues, thereby contributing to oncogenesis.

Bcl-2 Overexpression Leads to Increases in Suppressor of Cytokine Signaling-3 Expression in B Cells and De novo Follicular Lymphoma

The t(14;18)(q32;q21), resulting in deregulated expression of B-cell-leukemia/lymphoma-2 (Bcl-2), represents the genetic hallmark in human follicular lymphomas. Substantial evidence supports the hypothesis that the t(14;18) and Bcl-2 overexpression are necessary but not solely responsible for neoplastic transformation and require cooperating genetic derangements for neoplastic transformation to occur. To investigate genes that cooperate with Bcl-2 to influence cellular signaling pathways important for neoplastic transformation, we used oligonucleotide microarrays to determine differential gene expression patterns in CD19+ B cells isolated from Eμ-Bcl-2 transgenic mice and wild-type littermate control mice. Fifty-seven genes were induced and 94 genes were repressed by ≥2-fold in Eμ-Bcl-2 transgenic mice (P < 0.05). The suppressor of cytokine signaling-3 (SOCS3) gene was found to be overexpressed 5-fold in B cells from Eμ-Bcl-2 transgenic mice. Overexpression of Bcl-2 in both mouse embryo fibroblast-1 and hematopoietic cell lines resulted in induction of SOCS3 protein, suggesting a Bcl-2-associated mechanism underlying SOCS3 induction. Immunohistochemistry with SOCS3 antisera on tissue from a cohort of patients with de novo follicular lymphoma revealed marked overexpression of SOCS3 protein that, within the follicular center cell region, was limited to neoplastic follicular lymphoma cells and colocalized with Bcl-2 expression in 9 of 12 de novo follicular lymphoma cases examined. In contrast, SOCS3 protein expression was not detected in the follicular center cell region of benign hyperplastic tonsil tissue. These data suggest that Bcl-2 overexpression leads to the induction of activated signal transducer and activator of transcription 3 (STAT3) and to the induction of SOCS3, which may contribute to the pathogenesis of follicular lymphoma.

Aberrant expression of the tyrosine kinase receptor EphA4 and the transcription factor twist in Sézary syndrome identified by gene expression analysis

Sézary syndrome (Sz) is a malignancy of CD4+ memory skin-homing T cells and presents with erythroderma, lymphadenopathy, and peripheral blood involvement. To gain more insight into the molecular features of Sz, oligonucleotide array analysis was performed comparing gene expression patterns of CD4+ T cells from peripheral blood of patients with Sz with those of patients with erythroderma secondary to dermatitis and healthy controls. Using unsupervised hierarchical clustering gene, expression patterns of T cells from patients with Sz were classified separately from those of benign T cells. One hundred twenty-three genes were identified as significantly differentially expressed and had an average fold change exceeding 2. T cells from patients with Sz demonstrated decreased expression of the following hematopoietic malignancy-linked tumor suppressor genes: TGF-beta receptor II, Mxi1, Riz1, CREB-binding protein, BCL11a, STAT4, and Forkhead Box O1A. Moreover, the tyrosine kinase receptor EphA4 and the potentially oncogenic transcription factor Twist were highly and selectively expressed in T cells of patients with Sz. High expression of EphA4 and Twist was also observed in lesional skin biopsy specimens of a subset of patients with cutaneous T cell lymphomas related to Sz, whereas their expression was nearly undetectable in benign T cells or in skin lesions of patients with inflammatory dermatoses. Detection of EphA4 and Twist may be used in the molecular diagnosis of Sz and related cutaneous T-cell lymphomas. Furthermore, the membrane-bound EphA4 receptor may serve as a target for directed therapeutic intervention.

Suppressor of cytokine signaling 3 expression in anaplastic large cell lymphoma

Using a cDNA microarray, we found that suppressor of cytokine signaling 3 (SOCS3) is highly expressed in anaplastic lymphoma kinase (ALK)+ anaplastic large cell lymphoma (ALCL) cell lines. As SOCS3 is induced by activated signal transducer and activator of transcription 3 (STAT3), and ALK activates STAT3, we hypothesized that SOCS3 may play a role in ALK+ ALCL pathogenesis via the Janus kinase 3 (JAK3)-STAT3 pathway. Using ALCL cell lines, we show by coimmunoprecipitation experiments that SOCS3 physically binds with JAK3 in vitro, and that JAK3 inhibition by WHI-P154 downregulates SOCS3 expression. Western blot analysis confirmed expression of SOCS3 and also showed coexpression of phosphorylated (activated) STAT3 (pSTAT3). Direct sequencing of the SOCS3 gene showed no mutations or alternative splicing. In ALCL tumors that were assessed by immunohistochemistry, nine of 12 (75%) ALK+ tumors were SOCS3 positive and eight (67%) coexpressed pSTAT3. In comparison, 18 of 25 (72%) ALK-- tumors were SOCS3 positive and seven (28%) coexpressed pSTAT3. These results show that SOCS3 is overexpressed in ALCL, attributable to JAK3-STAT3 activation and likely related to ALK in ALK+ tumors. However, SOCS3 is also expressed in tumors that lack STAT3 and ALK suggesting alternative mechanisms of upregulation.

Tyrosine-phosphorylated SOCS3 Interacts with the Nck and Crk-L Adapter Proteins and Regulates Nck Activation

Suppressors of cytokine signaling (SOCS) are negative feedback inhibitors of cytokine and growth factor signal transduction. Although the affect of SOCS proteins on the Jak-STAT pathway has been well characterized, their role in the regulation of other signaling modules is not well understood. In the present study, we demonstrate that SOCS3 physically interacts with the SH2/SH3-containing adapter proteins Nck and Crk-L, which are known to couple activated receptors to multiple downstream signaling pathways and the actin cytoskeleton. Our data show that the SOCS3/Nck and SOCS3/Crk-L interactions depend on tyrosine phosphorylation of SOCS3 Tyr(221) within the conserved SOCS box motif and intact SH2 domains of Nck and Crk-L. Furthermore, SOCS3 Tyr(221) forms a YXXP motif, which is a consensus binding site for the Nck and Crk-L SH2 domains. Expression of SOCS3 in NIH3T3 cells induces constitutive recruitment of a Nck-GFP fusion protein to the plasma membrane and constitutive tyrosine phosphorylation of endogenous Nck. Our findings suggest that SOCS3 regulates multiple cytokine and growth factor-activated signaling pathways by acting as a recruitment factor for adapter proteins.

Effects of cardiotrophin on adipocytes

Cardiotrophin (CT-1) is a naturally occurring protein member of the interleukin (IL)-6 cytokine family and signals through the gp130/leukemia inhibitory factor receptor (LIFR) heterodimer. The formation of gp130/LIFR complex triggers the auto/trans-phosphorylation of associated Janus kinases, leading to the activation of Janus kinase/STAT and MAPK (ERK1 and -2) signaling pathways. Since adipocytes express both gp130 and LIFR proteins and are responsive to other IL-6 family cytokines, we examined the effects of CT-1 on 3T3-L1 adipocytes. Our studies have shown that CT-1 administration results in a dose- and time-dependent activation and nuclear translocation of STAT1, -3, -5A, and -5B as well as ERK1 and -2. We also confirmed the ability of CT-1 to induce signaling in fat cells in vivo. Our studies revealed that neither CT-1 nor ciliary neurotrophic factor treatment affected adipocyte differentiation. However, acute CT-1 treatment caused an increase in SOCS-3 mRNA in adipocytes and a transient decrease in peroxisome proliferator-activated receptor gamma (PPARgamma) mRNA that was regulated by the binding of STAT1 to the PPARgamma2 promoter. The effects of CT-1 on SOCS-3 and PPARgamma mRNA were independent of MAPK activation. Chronic administration of CT-1 to 3T3-L1 adipocytes resulted in a decrease of both fatty acid synthase and insulin receptor substrate-1 protein expression yet did not effect the expression of a variety of other adipocyte proteins. Moreover, chronic CT-1 treatment resulted in the development of insulin resistance as judged by a decrease in insulin-stimulated glucose uptake. In summary, CT-1 is a potent regulator of signaling in adipocytes in vitro and in vivo, and our current efforts are focused on determining the role of this cardioprotective cytokine on adipocyte physiology.

SOCS-1 and SOCS-3 inhibit IFN-alpha-induced expression of the antiviral proteins 2,5-OAS and MxA

Although the use of IFN-alpha in combination with ribavirin has improved the treatment efficacy of chronic hepatitis C virus (HCV) infection, 20-50% of patients still fail to eradicate the virus depending on the HCV genotype. Recently, overexpression of HCV core protein has been shown to inhibit IFN signaling and induce SOCS-3 expression. Aim of this study was to examine the putative role of SOCS proteins in IFN resistance. By Western blot analysis, a 4-fold induction of STAT-1/3 phosphorylation by IFN-alpha was observed in mock-transfected HepG2 clones. In contrast, IFN-induced STAT-1/3 phosphorylation was considerably downregulated by SOCS-1/3 overexpression. In mock-transfected cells, IFN-alpha induced 2',5'-OAS and myxovirus resistance A (MxA) promoter activity 40- to 80-fold and 10- to 35-fold, respectively, and this effect was abrogated in SOCS-1/3 overexpressing cells. As detected by Northern blot technique, IFN-alpha potently induced 2',5'-OAS and MxA mRNA expression in the control clones. Overexpression of SOCS-1 completely abolished both 2',5'-OAS and MxA mRNA expression, whereas SOCS-3 mainly inhibited 2',5'-OAS mRNA expression. Our results demonstrate that SOCS-1 and SOCS-3 proteins inhibit IFN-alpha-induced activation of the Jak-STAT pathway and expression of the antiviral proteins 2',5'-OAS and MxA. These data suggest a potential role of SOCS proteins in IFN resistance during antiviral treatment.

Selective inhibition of STAT3 induces apoptosis and G(1) cell cycle arrest in ALK-positive anaplastic large cell lymphoma

Nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) is an aberrant fusion gene product expressed in a subset of cases of anaplastic large cell lymphoma (ALCL). It has been shown that NPM-ALK binds to and activates signal transducer and activator of transcription 3 (STAT3) in vitro, and that STAT3 is constitutively active in ALK(+) ALCL cell lines and tumors. In view of the oncogenic potential of STAT3, we further examined its biological significance in ALCL using two ALK(+) ALCL cell lines (Karpas 299 and SU-DHL-1) and an adenoviral vector that carries dominant-negative STAT3 (AdSTAT3DN). Infection by AdSTAT3DN led to the expression of STAT3DN in both ALK(+) ALCL cell lines at a similar efficiency. Subcellular fractionation studies showed that a significant proportion of the expressed STAT3DN protein translocated to the nucleus, despite the fact that STAT3DN has a mutation at residue 705(tyrosine --> phenylalanine), a site that is believed to be crucial for STAT3 activation and nuclear translocation. Introduction of STAT3DN induced apoptosis and G(1) cell cycle arrest. Western blot studies showed that expression of STAT3DN resulted in caspase-3 cleavage, downregulation of Bcl-2, Bcl-xL, cyclin D3, survivin, Mcl-1, c-Myc and suppressor of cytokine signaling 3. These results support the concept that STAT3 activation is pathogenetically important in ALCL cells by deregulating the expression of multiple target proteins that are involved in the control of apoptosis and cell cycle progression.

The role of suppressors of cytokine signaling (SOCS) proteins in regulation of the immune response

Cytokines are an integral component of the adaptive and innate immune responses. The signaling pathways triggered by the engagement of cytokines with their specific cell surface receptors have been extensively studied and have provided a profound understanding of the intracellular machinery that translates exposure of cells to cytokine to a coordinated biological response. It has also become clear that cells have evolved sophisticated mechanisms to prevent excessive responses to cytokines. In this review we focus on the suppressors of cytokine signaling (SOCS) family of cytoplasmic proteins that completes a negative feedback loop to attenuate signal transduction from cytokines that act through the janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway. SOCS proteins inhibit components of the cytokine signaling cascade via direct binding or by preventing access to the signaling complex. The SOCS proteins also appear to target signal transducers for proteasomal destruction. Analyses of genetically modified mice in which SOCS proteins are overexpressed or deleted have established that this family of negative regulators has indispensable roles in regulating cytokine responses in cells of the immune system as well as other tissues. Emerging evidence also suggests that disruption of SOCS expression or activity is associated with several immune and inflammatory diseases, raising the prospect that manipulation of SOCS activity may provide a novel future therapeutic strategy in the management of immunological disorders.

In vivo activation of STAT3 in cutaneous T-cell lymphoma. Evidence for an antiapoptotic function of STAT3

A characteristic feature of neoplastic transformation is a perpetual activation of oncogenic proteins. Here, we studied signal transducers and activators of transcription (STAT) in patients with mycosis fungoides (MF)/cutaneous T-cell lymphoma (CTCL). Malignant lymphocytes in dermal infiltrates of CTCL tumors showed frequent and intense nuclear staining with anti-PY-STAT3 antibody, indicating a constitutive activation of STAT3 in vivo in tumor stages. In contrast, only sporadic and faint staining was observed in indolent lesions of patch and plaque stages of MF. Moreover, neoplastic lymphocytes in the epidermal Pautrier abscesses associated with early stages of MF did not express activated STAT3. To address the role of STAT3 in survival/apoptosis, CTCL tumor cells from an advanced skin tumor were transfected with either wild-type STAT3 (STAT3wt) or dominant-negative STAT3 (STAT3D). Forced inducible expression of STAT3D triggered a significant increase in tumor cells undergoing apoptosis, whereas forced expression of STAT3wt or empty vector had no effect. In conclusion, a profound in vivo activation of STAT3 is observed in MF tumors but not in the early stages of MF. Moreover, STAT3 protects tumor cells from apoptosis in vitro. Taken together, these findings suggest that STAT3 is a malignancy factor in CTCL.

Sezary Syndrome Cells Unlike Normal Circulating T Lymphocytes Fail to Migrate Following Engagement of NT1 Receptor

Circulating malignant Sezary cells are a clonal proliferation of CD4+CD45RO+ T lymphocytes primarily involving the skin. To study the biology of these malignant T lymphocytes, we tested their ability to migrate in chemotaxis assays. Previously, we had shown that the neuropeptide neurotensin (NT) binds to freshly isolated Sezary malignant cells and induces through NT1 receptors the cell migration of the cutaneous T cell lymphoma cell line Cou-L. Here, we report that peripheral blood Sezary cells as well as the Sezary cell line Pno fail to migrate in response to neurotensin although they are capable of migrating to the chemokine stromal-cell-derived factor 1 alpha. This is in contrast with normal circulating CD4+ or CD8+ lymphocytes, which respond to both types of chemoattractants except after ex vivo short-time anti-CD3 monoclonal antibody activation, which abrogates the neurotensin-induced lymphocyte migration. Furthermore, we demonstrate that neurotensin-responsive T lymphocytes express the functional NT1 receptor responsible for chemotaxis. In these cells, but not in Sezary cells, neurotensin induces recruitment of phosphatidylinositol-3 kinase, and redistribution of phosphorylated cytoplasmic tyrosine kinase focal adhesion kinase and filamentous actin. Taken together, these results, which show functional distinctions between normal circulating lymphocytes and Sezary syndrome cells, contribute to further understanding of the physiopathology of these atypical cells.

Advances in the diagnosis and classification of chronic lymphoproliferative disorders

In this review, we have highlighted recent advances in chronic lymphoproliferative disorders that commonly involve the peripheral blood. As we have seen, our concepts of certain diseases are changing. Molecular genetic and immunophenotypic studies are allowing more precise characterization of CLL and defining important biologic markers that predict clinical behavior. Prolymphocytic leukemia is now more narrowly defined and its relationship to nucleolated variants of MCL is now apparent. With new reagents and techniques applied to problems such as identification of Sezary cells and T-cell monoclonality determination, our ability to diagnose, monitor, and provide prognostic information is improving. Insight into the biology of these diseases also may provide new therapeutic targets in the future.

Histopathology and genetics of cutaneous T-cell lymphoma

There is emerging evidence that genomic and chromosomal instability are features of CTCL, including variants such as MF, Sézary syndrome, and primary cutaneous CD30+ LCAL, and that specific chromosomal abnormalities are common. Additional resolution of specific regions of chromosomal loss and gain are required to define putative genes that may be of fundamental pathogenetic importance in CTCL. Inactivation of well-defined cell cycle and TSG are common as for other types of NHL. The prognostic significance of these abnormalities in CTCL has yet to be determined. The dysregulation of specific transcription factors is of interest, but requires further study. It is hoped that greater understanding of these molecular abnormalities will permit the development of CTCL-specific therapies that alleviate suffering and prolong survival.

Suppressor of cytokine signalling gene expression is elevated in breast carcinoma

Cytokines are important for breast cell function, both as trophic hormones and as mediators of host defense mechanisms against breast cancer. Recently, inducible feedback suppressors of cytokine signalling (SOCS/JAB/SSI) have been identified, which decrease cell sensitivity to cytokines. We examined the expression of SOCS genes in 17 breast carcinomas and 10 breast cancer lines, in comparison with normal tissue and breast lines. We report elevated expression of SOCS-1-3 and CIS immunoreactive proteins within in situ ductal carcinomas and infiltrating ductal carcinomas relative to normal breast tissue. Significantly increased expression of SOCS-1-3 and CIS transcripts was also shown by quantitative in situ hybridisation within both tumour tissue and reactive stroma. CIS transcript expression was elevated in all 10 cancer lines, but not in control lines. However, there was no consistent elevation of other SOCS transcripts. CIS protein was shown by immunoblot to be present in all cancer lines at increased levels, mainly as the 47 kDa ubiquitinylated form. A potential proliferative role for CIS overexpression is supported by reports that CIS activates ERK kinases, and by strong induction in transient reporter assays with an ERK-responsive promoter. The in vivo elevation of SOCS gene expression may be part of the host/tumour response or a response to autocrine/paracrine GH and prolactin. However, increased CIS expression in breast cancer lines appears to be a specific lesion, and could simultaneously shut down STAT 5 signalling by trophic hormones, confer resistance to host cytokines and increase proliferation through ERK kinases.

Constitutive STAT3 activation in intestinal T cells from patients with Crohn's disease

Via cytoplasmic signal transduction pathways, cytokines induce a variety of biological responses and modulate the outcome of inflammatory diseases and malignancies. Crohn's disease is a chronic inflammatory bowel disease of unknown etiology. Perturbation of the intestinal cytokine homeostasis is believed to play a pivotal role, but the pathogenesis of Crohn's disease is not fully understood. Here, we study intestinal T cells from Crohn's disease and healthy volunteers. We show that STAT3 and STAT4 are constitutively activated in Crohn's patients but not in healthy volunteers. The activation is specific, because other STAT proteins are not constitutively activated. Furthermore, the STAT3 regulated protein, SOCS3, is also constitutively expressed in Crohn's patients but not in healthy volunteers. Taken together, these data provide evidence of abnormal STAT/SOCS signaling in Crohn's disease. This aberrant activation, so far noted only in malignant cells, establish a new critical approach for better understanding the immunopathogenesis of Crohn's disease.

Molecular cytogenetic characterization of Sézary syndrome

Sézary syndrome (SS) is a rare form of erythrodermic cutaneous T-cell lymphoma with hematological involvement and a poor prognosis. At present little is known about the molecular pathogenesis of this malignancy. To address this issue, we analyzed 28 SS cases through the use of molecular cytogenetic techniques. Conventional cytogenetic analysis showed 12 of 28 cases with clonal chromosome abnormalities (43%). Seven cases had aberrations affecting chromosomes 1 and 17; five demonstrated rearrangement of chromosomes 10 and 14; four presented with an abnormality of 6q. Multiplex-fluorescence in situ hybridization (M-FISH) revealed complex karyotypes in 6 of 17 cases (35%), and recurrent der(1)t(1;10)(p2;q2) and der(14)t(14;15)(q;q?) translocations were each identified in two cases, and confirmed by dual-color FISH. There was an overall difference in the incidence of clonal abnormalities detected by G-banded karyotyping and M-FISH. In addition, comparative genomic hybridization studies revealed chromosome imbalances (CIs) in 9 of 20 cases (45%), with a mean DNA copy number change per sample of 1.95 +/- 2.74, and losses (mean: 1.25 +/- 1.77) more frequent than gains (mean: 0.7 +/- 1.26). The most common CIs noted were loss of 1p, followed by losses of 10/10q, 17p, and 19, and gains of 17q and 18. Furthermore, in conjunction with this study a systematic literature review was conducted, which showed a high frequency and consistent pattern of chromosome changes in SS. These findings suggest that chromosomal instability is common in SS, although there are specific chromosomal abnormalities that appear to be characteristic, and the identification of two different recurrent chromosome translocations provides the basis for further studies.

Regulatory effect of SOCS on NF-kappaB activity in murine monocytes/macrophages

The suppressor of cytokine signaling (SOCS) group of proteins has been implicated in regulation of various cytokine signaling and in a negative crosstalk between distinct signaling pathways. Interleukin-10 (IL-10) and LPS were known to induce expression of SOCS-3 in neutrophils and monocytes/macrophages. IL-10 was also reported to inhibit a proinflammatory signal-induced NF-kappaB activation in monocytes and peripheral T lymphocytes. The effects of increased SOCS-3 expression upon IL-10 regulation of NF-kappaB activation have not yet been demonstrated. Here we examined the effects of SOCS-3 on NF-kappaB activity. SOCS-3 did not induce any alterations in NF-kappaB activity induced by LPS or TNF-alpha. However, it enhanced RelA-dependent kappaB promoter activity when cotransfected with RelA. Similar results were observed with SOCS-1. In contrast, SOCS-2 did not show any regulatory effects on RelA activity. Analysis of C-terminal truncation mutants of SOCS-1 and SOCS-3 demonstrated that the SOCS box and its N-terminal region, a less well-conserved linker region were important for SOCS-3 activation of RelA. In contrast, the SOCS box itself was critical for SOCS-1 to activate RelA. These results suggest that SOCS proteins can enhance the effects of NF-kappaB/Rel proteins, and therefore, further modulate immune and inflammatory responses.

Protein phosphatase 2A (PP2A) regulates interleukin-4-mediated STAT6 signaling

Interleukin-4 (IL-4) plays a pivotal role in the induction and maintenance of allergy by promoting Th2 differentiation and B cell isotype switching to IgE. Studies on STAT6-deficient mice have demonstrated the essential role of STAT6 in mediating the biological functions of IL-4. IL-4 induces tyrosine phosphorylation of STAT6, which in turn leads to transcription of IL-4-specific genes. In addition, serine phosphorylation of STAT6 has recently been reported. Here we study the functional role of STAT6 serine phosphorylation and the kinases and phosphatases involved. We show that inhibition of protein phosphatase 2A (PP2A) induces serine phosphorylation of STAT6 and severely inhibits DNA binding of STAT6. In contrast, IL-4-induced tyrosine phosphorylation of Janus kinase-1 and STAT6 is not affected, suggesting that PP2A acts downstream of Janus kinases in IL-4 signaling. In conclusion, we provide the first evidence that PP2A plays a crucial role in the regulation of STAT6 function.

SHP2 regulates IL-2 induced MAPK activation, but not Stat3 or Stat5 tyrosine phosphorylation, in cutaneous T cell lymphoma cells

The phosphotyrosine phosphatase SHP2 has been suggested to regulate activation of MAPK, Stat3, and Stat5 in several experimental models. In this study we investigated the role of SHP2 in IL-2 induced activation of MAPK and the Stat proteins using the human CTCL cell line MyLa2059 derived from a cutaneous T cell lymphoma (CTCL). For this purpose, MyLa2059 cells were stably transfected with wild-type SHP2 or inactive SHP2. The cells transfected with inactive SHP2 showed reduced MAPK activation upon IL-2 stimulation, suggesting that SHP2 upregulates IL-2 induced MAPK activation in T cells. However, the constitutive tyrosine phosphorylation of Stat3 as well as IL-2 induced Stat5 tyrosine phosphorylation and DNA binding were unaffected by the stably transfected wild-type SHP2 as well as the inactive SHP2. In conclusion, we show for the first time that SHP2 positively regulates IL-2 induced MAPK activation in malignant T cells. Furthermore, the results indicate that SHP2 may not be involved in the activation of Stat3 or Stat5 in CTCL cells.

Constitutive expression of SOCS3 confers resistance to IFN-alpha in chronic myelogenous leukemia cells

Because suppressor of cytokine signaling (SOCS) proteins are negative regulators of cytokine-induced signaling, it has been hypothesized that aberrant SOCS expression confers resistance against cytokine therapy. This study reports on the constitutive expression of SOCS3 in most chronic myelogenous leukemia (CML) cell lines, which are resistant to treatment with interferon alpha (IFN-alpha). In contrast, the KT-1/A3 cell line, in which constitutive expression of SOCS3 is barely detectable, is sensitive to IFN-alpha treatment. Forced expression of SOCS3 in the KT-1/A3 cell line confers resistance to IFN-alpha treatment. Furthermore, most of the blast cells from patients in CML blast crisis, which are usually resistant to IFN-alpha therapy, showed constitutive expression of SOCS3. These findings indicate that constitutive SOCS3 expression affects the IFN-alpha sensitivity of CML cell lines and blast cells from patients with CML blast crisis.

Molecular cytogenetic analysis of cutaneous T-cell lymphomas: identification of common genetic alterations in Sézary syndrome and mycosis fungoides

BACKGROUND

Data on genome-wide surveys for chromosome aberrations in primary cutaneous T-cell lymphoma (CTCL) are limited.

OBJECTIVE

To investigate genetic aberrations in CTCL.

METHODS

We analysed 18 cases of Sézary syndrome (SS) and 16 cases of mycosis fungoides (MF) by comparative genomic hybridization (CGH) analysis, and correlated findings with the results of additional conventional cytogenetics, fluorescent in situ hybridization (FISH) and allelotyping studies.

RESULTS

CGH analysis showed chromosome imbalances (CIs) in 19 of 34 CTCL cases (56%). The mean +/- SD number of CIs per sample was 1.8 +/- 2.4, with losses (1.2 +/- 2.0) slightly more frequent than gains (0.6 +/- 1.0). The most frequent losses involved chromosomes 1p (38%), 17p (21%), 10q/10 (15%) and 19 (15%), with minimal regions of deletion at 1p31p36 and 10q26. The commonly detected chromosomal gains involved 4/4q (18%), 18 (15%) and 17q/17 (12%). Both SS and late stages of MF showed a similar pattern of CIs, but no chromosomal changes were found in three patients with T1 stage MF. Of the 18 SS cases also analysed by cytogenetics, seven showed clonal chromosome abnormalities (39%). Five cases had structural aberrations affecting chromosomes 10 and 17, four demonstrated rearrangement of 1p and three revealed an abnormality of either 6q or 14q consistent with CGH findings. FISH analysis showed chromosome 1p and 17q rearrangements in five of 15 SS cases, and chromosome 10 abnormalities in four SS cases consistent with both the G-banded karyotype and the CGH results. In addition, allelotyping analysis of 33 MF patients using chromosome 1 markers suggested minimal regions of deletion at D1S228 (1p36), D1S2766 (1p22) and D1S397 (1q25).

CONCLUSIONS

These findings provide a comprehensive assessment of genetic abnormalities in CTCL and a rational approach for further studies.

SHP-1 expression in peripheral T cells from patients with Sezary syndrome and in the T cell line HUT-78: implications in JAK3-mediated signaling

SHP-1 is a key tyrosine phosphatase that acts as a negative regulator of signal transduction in lymphocytes, which has been found down-regulated in several T cell lines derived from human T cell malignancies. The standardization of a sensitive ELISA for the quantification of SHP-1 protein in peripheral T and B lymphocytes has enabled us to quantify the SHP-1 content of freshly isolated T cells from patients with Sezary syndrome and in the Sezary T cell line HUT-78. In all cases, a dramatic decrease in the content of this protein, when compared with the content in healthy volunteer controls, was observed. These results were corroborated when the expression of SHP-1 mRNA was analyzed. In order to study whether there was any correlation between SHP-1 protein expression and tyrosine phosphorylated state of JAK3, the state of phosphorylation of JAK3 was studied in the T cell line HUT-78, and found to be highly phosphorylated. These results suggest that SHP-1 might be involved in maintaining the IL-2R/JAK3 signaling pathway under control and point towards a role of SHP-1 in the pathogenesis of the disease.

Spontaneous interleukin-5 production in cutaneous T-cell lymphoma lines is mediated by constitutively activated Stat3

Mycosis fungoides is a low-grade cutaneous T-cell lymphoma (CTCL) of unknown etiology. In advanced stages of CTCL, a shift in cytokine profile from T(H)1 to T(H)2 is observed, which coincides with eosinophilia, high levels of immunoglobulin E, and increased susceptibility to bacterial infections. It is, however, unknown why T(H)2 cytokines predominate in advanced CTCL, and the cellular source of these cytokines also remains to be identified. In several leukemias and lymphomas, constitutively activated signal transducer and activator of transcription (Stat) signaling pathways have been detected. In a previous study, constitutive activation of Stat3 was found in tumor cells isolated from affected skin and blood from CTCL patients. Here, it is shown that CTCL tumor cell lines, but not nonmalignant cell lines, spontaneously produce interleukin-5 (IL-5), IL-6, and IL-13. Transfection of tumor cells with dominant-negative Stat3 almost completely blocks IL-5 production and strongly inhibits IL-13 production, whereas IL-6 production is unaffected. Thus, the data show that malignant CTCL cells themselves might contribute to the change in cytokine pattern accompanying progression of CTCL. In conclusion, constitutively activated Stat3 is found to mediate a spontaneous IL-5 production and regulate IL-13 production in CTCL cell lines, pointing toward a new role of Stat3 in malignant transformation.

Interleukin-7 and interleukin-15 regulate the expression of the bcl-2 and c-myb genes in cutaneous T-cell lymphoma cells

Interleukin-7 (IL-7) and IL-15 have been recently identified as growth factors for cutaneous T-cell lymphoma (CTCL) cells, and they protect these cells from cell death. Using the CTCL cell line SeAx as a test system now shows that IL-7 and IL-15 are indeed necessary to maintain high levels of bcl-2. The up-regulation of bcl-2 was paralleled by increased DNA-binding activities of the transcription factors STAT2, STAT5, STAT6, and c-Myb to bcl-2 gene promoter-enhancer elements. Because STAT5 and c-Myb positively regulate bcl-2, IL-7 and IL-15 may mediate some of their effects on cell death survival gene expression through these 2 factors. Constitutive activities of the 3 STAT factors and c-Myb were found in the IL-7- and IL-15-independent CTCL cell lines HUT78 and MyLa 2059. The c-Myb protein was also present in CTCL cells of the skin lesions of all investigated patients. These results indicate that IL-7 and IL-15 may increase bcl-2 expression in CTCL cells by the activation of c-myb and STAT factors.

Constitutive and interleukin-7- and interleukin-15-stimulated DNA binding of STAT and novel factors in cutaneous T cell lymphoma cells

On testing cutaneous T cell lymphoma cell lines and skin lesions, we found that the transcription factors STAT2, STAT3, STAT5, and STAT6 (STAT, signal transducer and activator of transcription) were present in the nuclei of these cells and that the binding to their specific DNA binding sites was stimulated by interleukin-7 and interleukin-15. DNA binding studies also revealed the presence of three additional DNA factors in cutaneous T cell lymphoma cells that bound to the same sequences and could also be stimulated by interleukin-7 and interleukin-15. One of these novel factors was also present in the adult T cell leukemia cell line Jurkat and malignant T cells from the blood of Sézary syndrome patients, but not in normal peripheral blood lymphocytes. It may therefore be a marker of T cell leukemia. It seems to interfere with the binding of STAT1 to the sis inducible element, suggesting that the DNA binding activity of STAT1 in cutaneous T cell lymphoma cells is disturbed.

Interferon-alpha induces transient suppressors of cytokine signalling expression in human T cells

The suppressors of cytokine signalling (SOCS) proteins comprise a newly identified family of negative feedback regulators of cytokine signalling. SOCS expression is differentially induced upon cytokine stimulation in different cell types. Here we show that interferon-alpha (IFNalpha) is a potent inducer of SOCS expression in human T cells, as high expression of CIS, SOCS-1, SOCS-2, and SOCS-3 was detectable after IFNalpha stimulation. After 4 h of stimulation, CIS, SOCS-1, and SOCS-3 expression had returned to baseline levels, whereas SOCS-2 expression had not declined. In contrast, after IL-2 induction neither CIS, SOCS-1, nor SOCS-2 expression levels declined after 6 h. In conclusion, we provide the first evidence that IFNalpha induces SOCS expression in human T cells. Moreover, we show that IFNalpha and IL-2 induce distinct patterns of expression kinetics, suggesting that dynamic changes in cytokine sensitivity might be mediated via induction of SOCS expression with different kinetics in T cells.