Constitutional activation of IL-6-mediated JAK/STAT pathway through hypermethylation of SOCS-1 in human gastric cancer cell line

The interleukin-mediated Janus kinase (JAK)/STAT pathway plays a crucial role in carcinogenesis. Recently, increased STAT3 activity was found in hepatocellular carcinoma and multiple myeloma in which there was silencing of SOCS-1 (suppressor of cytokine signalling-1) by gene promoter hypermethylation. We investigated the expression level of interleukin-6 (IL-6) and SOCS-1 in gastric cancer cell lines. Expression of SOCS-1 correlated with IL-6 level in most of the cell lines, except for AGS cells in which SOCS-1 was absent despite a high level of IL-6 production. Methylation analysis by methylation-specific polymerase chain reaction and bisulphite sequencing revealed that CpG island of SOCS-1 was densely methylated in AGS cells. Demethylation treatment by 5'aza-deoxycytidine restored SOCS-1 expression and also suppressed constitutive STAT3 phosphorylation in AGS cells. Moreover, methylation of SOCS-1 was detected in 27.5% (11 of 40) of primary gastric tumours samples, 10% (one of 10) of adjacent noncancer tissues but not in any (zero of nine) normal gastric mucosa. Methylation of SOCS-1 also correlated with the loss of mRNA expression in some primary gastric cancers. In conclusion, this is the first report to demonstrate that hypermethylation of SOCS-1 led to gene silencing in gastric cancer cell line and primary tumour samples. Downregulation of SOCS-1 cooperates with IL-6 in the activation of JAK/STAT pathway in gastric cancer.     

Silencing of Suppressor of Cytokine Signaling-3 due to Methylation Results in Phosphorylation of STAT3 in Imatinib Resistant BCR-ABL Positive Chronic Myeloid Leukemia Cells

Background: Silencing due to methylation of suppressor of cytokine signaling-3 (SOCS-3), a negative regulatorgene for the JAK/STAT signaling pathway has been reported to play important roles in leukemogenesis. Imatinibmesylate is a tyrosine kinase inhibitor that specifically targets the BCR-ABL protein and induces hematologicalremission in patients with chronic myeloid leukemia (CML). Unfortunately, the majority of CML patientstreated with imatinib develop resistance under prolonged therapy. We here investigated the methylation profileof SOCS-3 gene and its downstream effects in a BCR-ABL positive CML cells resistant to imatinib. Materials andMethods: BCR-ABL positive CML cells resistant to imatinib (K562-R) were developed by overexposure of K562cell lines to the drug. Cytotoxicity was determined by MTS assays and IC50 values calculated. Apoptosis assayswere performed using annexin V-FITC binding assays and analyzed by flow cytometry. Methylation profileswere investigated using methylation specific PCR and sequencing analysis of SOCS-1 and SOCS-3 genes. Geneexpression was assessed by quantitative real-time PCR, and protein expression and phosphorylation of STAT1,2 and 3 were examined by Western blotting. Results: The IC50 for imatinib on K562 was 362nM compared to3,952nM for K562-R (p=0.001). Percentage of apoptotic cells in K562 increased upto 50% by increasing theconcentration of imatinib, in contrast to only 20% in K562-R (p<0.001). A change from non-methylation ofthe SOCS-3 gene in K562 to complete methylation in K562-R was observed. Gene expression revealed downregulationof both SOCS-1 and SOCS-3 genes in resistant cells. STAT3 was phosphorylated in K562-R but notK562. Conclusions: Development of cells resistant to imatinib is feasible by overexposure of the drug to the cells.Activation of STAT3 protein leads to uncontrolled cell proliferation in imatinib resistant BCR-ABL due to DNAmethylation of the SOCS-3 gene. Thus SOCS-3 provides a suitable candidate for mechanisms underlying thedevelopment of imatinib resistant in CML patients.     

Mutations of the tumor suppressor gene SOCS-1 in classical Hodgkin lymphoma are frequent and associated with nuclear phospho-STAT5 accumulation

The suppressors of cytokine signaling (SOCS) are critically involved in the regulation of cellular proliferation, survival, and apoptosis via cytokine-induced JAK/STAT signaling. SOCS-1 silencing by aberrant DNA methylation contributes to oncogenesis in various B-cell neoplasias and carcinomas. Recently, we showed an alternative loss of SOCS-1 function due to deleterious SOCS-1 mutations in a major subset of primary mediastinal B-cell lymphoma (PMBL) and in the PMBL line MedB-1, and a biallelic SOCS-1 deletion in PMBL line Karpas1106P. For both cell lines our previous data demonstrated retarded JAK2 degradation and sustained phospho-JAK2 action leading to enhanced DNA binding of phospho-STAT5. Here, we analysed SOCS-1 in laser-microdissected Hodgkin and Reed-Sternberg (HRS) cells of classical Hodgkin lymphoma (cHL). We detected SOCS-1 mutations in HRS cells of eight of 19 cHL samples and in three of five Hodgkin lymphoma (HL)-derived cell lines by sequencing analysis. Moreover, we found a significant association between mutated SOCS-1 of isolated HRS cells and nuclear phospho-STAT5 accumulation in HRS cells of cHL tumor tissue (P < 0.01). Collectively, these findings support the concept that PMBL and cHL share many overlapping features, and that defective tumor suppressor gene SOCS-1 triggers an oncogenic pathway operative in both lymphomas.     

地西他滨对人急性髓系白血病细胞株HL-60的调控作用及其机制研究

目的 研究地西他滨(DAC)对人急性髓系白血病细胞株HL-60体外生长及自然杀伤(NK)细胞活化性受体配体(NKG2DL)表达的调节作用,并探讨JAK-STAT3-SOCS信号通路相关的分子机制.方法 CCK-8法检测DAC对HL-60细胞增殖活性的影响,Annexin-V/PI双标法检测细胞凋亡,流式细胞术检测HL-60细胞表面NKG2DL分子MICA/B、ULBP的表达,羧基荧光素双乙酸盐(CFSE)法检测NK细胞的杀伤活性,蛋白印迹法分析细胞内JAK-STAT3通路中STAT3、STAT3上游激酶JAK1、JAK2及STAT3活性负调控因子细胞因子信号抑制物(SOCS)-1、SOCS-3的蛋白表达水平,甲基化敏感性高分辨率熔解曲线分析(MS-HRM)检测DAC处理后SOCS-1、SOCS-3基因甲基化程度.结果 DAC可抑制HL-60细胞活性:0.2、0.5和1.0 μmol/L DAC处理48 h,HL-60细胞活性较对照组分别下降(25±11)%、(39±8)%和(50±7)%(P<0.01);48 h时,细胞凋亡发生率分别为(24.77±7.50)%、(27.10±4.48)%和(30.53±3.93)%,均较对照组细胞的(3.11±0.50)%增加(P<0.01).DAC可诱导HL-60细胞表面MICA/B、ULBP-1及ULBP-3分子的表达增高,增强HL-60细胞对NK细胞的杀伤敏感性.DAC处理后HL-60细胞内STAT3、JAK1、JAK2及p-STAT3、p-JAK1、p-JAK2表达下降,SOCS-1和SOCS-3蛋白表达增高.DAC可抑制SOCS-3基因甲基化.结论 DAC抑制人急性髓系白血病细胞株HL-60增殖,上调HL-60细胞对NKG2DL的表达,增强NK细胞对其的杀伤活性,其机制可能与细胞内JAK-STAT3-SOCS信号通路的活性调控有关.     

Leptin receptor expression and cell signaling in breast cancer

Obesity is considered a risk factor for many cancers, including breast cancer. Our laboratory has previously shown that leptin is mitogenic in many cancer cell lines, including breast. Information regarding the effects of high leptin levels on leptin receptor expression and signaling is lacking. The purpose of this study was to characterize leptin receptor expression in response to leptin in breast cancer cells. In addition, SOCS-3 expression (a leptin inducible inhibitor of leptin signaling), plus MAPK and PI3K signaling, were examined to determine their role in leptin-induced cell proliferation. Breast cancer cell lines, ZR75-1 and HTB-26, were treated with 0, 4, 40 or 80 ng/ml of leptin. Multiplex RT-PCR was performed to determine relative mRNA expression levels of the human short (huOB-Ra) or long (huOB-Rb) leptin receptor isoforms, or SOCS-3. MAPK and PI3K signaling was analyzed by phosphorylation of ERK and Akt, respectively, via Western blotting. Cell proliferation and inhibitor studies were analyzed by MTT assay. HTB-26 and ZR75-1 both expressed huOB-Ra, huOB-Rb and SOCS-3 mRNA; however, mRNA expression levels generally remained unchanged over time with leptin treatment. MAPK and PI3K pathways were activated in the presence of leptin over time. MAPK and PI3K inhibitors significantly blocked leptin-induced proliferation. Higher levels of circulating leptin contribute to breast cancer proliferation by activation of the MAPK and PI3K signaling pathways involved in cell growth and survival. The mitogenic effects of leptin are not a consequence of altered leptin receptor or SOCS-3 mRNA expression.     

Suppressor of cytokine signaling-1 expression by infectivity-enhanced adenoviral vector inhibits IL-6-dependent proliferation of multiple myeloma cells

Multiple myeloma (MM) accounts for 10% of hematological malignant disorders. Its refractory nature indicates the necessity of developing novel therapeutic modalities. Since interleukin 6 (IL-6) is one of the major growth factors for MM cells, we expressed suppressor of cytokine signaling-1 (SOCS-1), one of the blockades of IL-6 receptor downstream signaling, to suppress the proliferation of MM cells. Because MM cells are resistant to conventional adenoviral vector infection, we utilized infectivity-enhanced adenoviral vectors with an RGD4C motif in the adenoviral fiber-knob region (RGD-modified vector). In infectivity analysis, RGD-modified vectors were superior to unmodified controls in the majority of the MM cell lines tested. The overexpression of SOCS-1 using infectivity-enhanced adenoviral vectors achieved growth suppression in IL-6-dependent MM cells, but not in the IL-6-independent cells. IL-6-induced STAT3 phosphorylation was suppressed in IL-6-dependent cells, indicating that the signal transduction cascade of the IL-6 receptor signaling was blocked. In aggregate, SOCS-1 overexpression with RGD-modified adenoviral vectors achieved the antiproliferative effect in IL-6-dependent MM cells. These results provide an initial proof-of-principle of the anticancer effect of SOCS-1 expression vector as well as a promise for the future development of therapeutic modality for MM based on this vector.     

三氧化二砷诱导骨髓瘤细胞SOCS-1基因去甲基化及其对P—STAT3蛋白表达的影响

目的探讨三氧化二砷（AS2O3）对多发性骨髓瘤（MM）细胞内细胞因子信号转导抑制因子-1（SOCS-1）基因甲基化状态的影响及其对磷酸化的信号转导与转录激活因子-3（P．STA33）表达的影响。方法采用甲基特异性PCR法检测AS2O3作用前后MM细胞株U266和CZ-1细胞内SOCS-1基因的甲基化状态,应用蛋白免疫印迹法检测AS2O3处理前后细胞内P—STAT3蛋白的表达变化,并采用流式细胞技术检测AS2O3作用前后MM细胞增殖和凋亡的变化。结果MM细胞株内SOCS-1基因存在程度不同的甲基化状态,与对照组相比,AS2O3作用后MM细胞内SOCS-1基因甲基化程度明显减弱或消失,P—STAT3蛋白的表达也明显减弱,同时细胞生长受抑,凋亡比率升高。AS2O3浓度分别为0、0．5、1．0、2．0μmol／L时,U266细胞株的总凋亡率分别为0．06％、0．56％、48．96％、61．07％（x2=9．19,P〈0．05）;而CZ-1细胞株的总凋亡率分别为4．20％、40．30％、47．72％、68．49％（X2=8．96,P〈0．05）。结论AS2O3可能通过诱导MM细胞内SOCS-1基因去甲基化作用,进-步抑制细胞增殖信号Janus激酶（JAK）-STAT通路的活化,从而诱导MM细胞的凋亡。     

Expression and tyrosine phosphorylation of phosphatidyl-inositol-3 kinase in human gastric-cancer cells - its correlation with cell-growth

To reveal the signaling pathway leading to oncogenecity of human cancer cells, we examined the expression and tyrosine-phosphorylation of phosphatidylinositol (PI)-3 kinase in cancer cell lines. Of the 14 cell lines examined, two poorly differentiated human gastric cancer cell lines, NUGC-4 and MKN-45, which were previously found to have aberrant elevation of tyrosine phosphorylation showed elevated levels of PI-3 kinase 85-kDa subunit expression. In these cells, tyrosine-phosphorylation and overall activity of PI-3 kinase were apparently elevated, compared with normal human fibroblasts and another well differentiated gastric cancer cell line, MKN-28. Treatment of these cells with tyrosine kinase inhibitor, genistein, strongly suppressed the PI-3 kinase activity. Furthermore, wortmannin, a potent inhibitor of PI-3 kinase, strongly suppressed the growth of these gastric cancer cells. These results suggest that the growth signaling via tyrosine phosphorylation is required for the activation of PI-3 kinase in NUGC4 and MKN-45, and that this activation plays an important role in oncogenic growth of these cells. However, these two cell lines showed different responses of PI-3 kinase to acid-treatment and tyrosine kinase inhibitors. In MKN-45, activation of PI-3 kinase appeared to be constitutive, and could be relevant to the oncogenic nature of the cell line.     

β-Escin sodium inhibits inducible nitric oxide synthase expression via downregulation of the JAK/STAT pathway in A549 cells

β‐escin, a triterpene saponin, is one of the major active compounds extracted from horse chestnut (Aesculus hippocastanum) seed. Previous work has found that β‐escin sodium has antiinflammatory and antitumor effects. In the present study, we investigated its effect on cell proliferation and inducible nitric‐oxide synthase (iNOS) expression in human lung carcinoma A549 cells. β‐escin sodium (5–40 µg/mL) inhibited cytokine mixture (CM)‐induced nitric oxide (NO) production in A549 cells by reducing the expression of iNOS. β‐escin sodium suppressed phosphorylation and nuclear translocation of STAT1 (Tyr701) and STAT3 (Tyr705) induced by CM but did not affect the activation of c‐Jun and NF‐κB. β‐escin sodium inhibited the activation of protein tyrosine kinase JAK2. Pervanadate treatment reversed the β‐escin sodium‐induced downregulation of STAT3 and STAT1. β‐escin sodium treatment enhanced an activating phosphorylation of the phosphatase SHP2. Small interfering RNA‐mediated knockdown of SHP2 inhibited β‐escin sodium‐induced phospho‐STAT dephosphorylation. Moreover β‐escin sodium reduced the activation of p38 MAPK. Finally, β‐escin sodium inhibited the proliferation of A549 cells, did not change the cell membrane's permeability, nuclear morphology and size and the mitochondria's transmembrane potential of A549 cells. Taken together, these results demonstrate that β‐escin sodium could downregulate iNOS expression through inhibiting JAK/STAT signaling and p38 MAPK activation in A549 cells. β‐escin sodium has a marked antiproliferative effect on A549 cells at least in part by inhibiting the JAK/STAT signaling pathway, but not by a cytotoxic effect. β‐escin sodium would be useful as a chemopreventive agent or a therapeutic against inflammatory‐associated tumor. © 2011 Wiley Periodicals, Inc.     

三氧化二砷诱导骨髓瘤细胞SOCS-1基因-去甲基化及其对P-STAT3蛋白表达的影响

 目的 探讨三氧化二砷（AS₂O₃) 对多发性骨髓瘤 (MM) 细胞内细胞因子信号转导抑制因子-1（SOCS-1）基因甲基化状态的影响及其对磷酸化的信号转导与转录激活因子-3（P-STAT3）表达的影响。方法 采用甲基特异性PCR法检测AS₂O₃作用前后MM细胞株U266和CZ-1细胞内 SOCS-1基因的甲基化状态,应用蛋白免疫印迹法检测AS₂O₃处理前后细胞内P-STAT3蛋白的表达变化,并采用流式细胞技术检测AS₂O₃作用前后MM细胞增殖和凋亡的变化。结果 MM细胞株内SOCS-1基因存在程度不同的甲基化状态,与对照组相比,AS₂O₃作用后MM细胞内SOCS-1基因甲基化程度明显减弱或消失,P-STAT3蛋白的表达也明显减弱,同时细胞生长受抑,凋亡比率升高。AS₂O₃浓度分别为0、0.5、1.0、2.0 μmol/L时,U266细胞株的总凋亡率分别为0.06%、0.56%、48.96%、61.07%（χ²=9.19,P<0.05）;而CZ-1细胞株的总凋亡率分别为4.20%、40.30%、47.72%、68.49%（χ²=8.96,P<0.05）。结论 AS₂O₃可能通过诱导MM细胞内SOCS-1基因去甲基化作用,进一步抑制细胞增殖信号Janus激酶（JAK）-STAT通路的活化,从而诱导MM细胞的凋亡。