IL‐6 enriched lung cancer stem‐like cell population by inhibition of cell cycle regulators via DNMT1 upregulation

Tumors are influenced by a microenvironment rich in inflammatory cytokines, growth factors and chemokines, which may promote tumor growth. Interleukin‐6 (IL‐6) is a multifunctional cytokine and known as a regulator of immune and inflammation responses. IL‐6 has also been reported to be associated with tumor progression and chemoresistance in different types of cancers. In our study, we demonstrated that IL‐6 enriches the properties of lung cancer stem‐like cells in A549 lung cancer cells cultured in spheroid medium. IL‐6 also promotes sphere formation and stem‐like properties of A549 cells by enhancing cell proliferation. Methylation‐specific polymerase chain reaction (PCR) was performed and revealed that IL‐6 increased methylation of p53 and p21 in A549 cancer cells. Western blot analysis and quantitative real‐time PCR demonstrated that IL‐6 increased the expression of DNA methyltransferase 1 (DNMT1) in A549 cells cultured in spheroid medium, but not the expression of DNMT3a or DNMT3b. Knockdown of DNMT1 eliminated IL‐6‐mediated hypermethylation of cell cycle regulators and enrichment of lung cancer stem‐like properties. In conclusion, our study, for the first time, shows that the IL‐6/JAK2/STAT3 pathway upregulates DNMT1 and enhances cancer initiation and lung cancer stem cell (CSC) proliferation by downregulation of p53 and p21 resulting from DNA hypermethylation. Upon blockage of the IL‐6/JAK2/STAT3 pathway and inhibition of DNMT1, the proliferation of lung CSCs was reduced and their formation of spheres and ability to initiate tumor growth were decreased. These data suggest that targeting of the IL‐6/JAK2/STAT3 signaling pathway and DNMT1 may become important strategies for treating lung cancer.     

Cucurbitacin-I inhibits Aurora kinase A,Aurora kinase B and survivin,induces defects in cell cycle progression and promotes ABT-737-induced cell death in a caspase-independent manner in malignant human glioma cells

Because STAT signaling is commonly activated in malignant gliomas as a result of constitutive EGFR activation, strategies for inhibiting the EGFR/JAK/STAT cascade are of significant interest. We, therefore, treated a panel of established glioma cell lines, including EGFR overexpressors, and primary cultures derived from patients diagnosed with glioblastoma with the JAK/STAT inhibitor cucurbitacin-I. Treatment with cucurbitacin-I depleted p-STAT3, p-STAT5, p-JAK1 and p-JAK2 levels, inhibited cell proliferation, and induced G2/M accumulation, DNA endoreduplication, and multipolar mitotic spindles. Longer exposure to cucurbitacin-I significantly reduced the number of viable cells and this decrease in viability was associated with cell death, as confirmed by an increase in the subG1 fraction. Our data also demonstrated that cucurbitacin-I strikingly downregulated Aurora kinase A, Aurora kinase B and survivin. We then searched for agents that exhibited a synergistic effect on cell death in combination with cucurbitacin-I. We found that cotreatment with cucurbitacin-I significantly increased Bcl^-2/Bcl^-xL family member antagonist ABT-737-induced cell death regardless of EGFR/PTEN/p53 status of malignant human glioma cell lines. Although >50% of the cucurbitacin-I plus ABT-737 treated cells were annexin V and propidium iodide positive, PARP cleavage or caspase activation was not observed. Pretreatment of z-VAD-fmk, a pan caspase inhibitor did not inhibit cell death, suggesting a caspase-independent mechanism of cell death. Genetic inhibition of Aurora kinase A or Aurora kinase B or survivin by RNA interference also sensitized glioma cells to ABT-737, suggesting a link between STAT activation and Aurora kinases in malignant gliomas.     

Induction of metastatic potential by TrkB via activation of IL6/JAK2/STAT3 and PI3K/AKT signaling in breast cancer

In metastatic breast cancers, the acquisition of metastatic ability, which leads to clinically incurable disease and poor survival, has been associated with acquisition of epithelial-mesenchymal transition (EMT) program and self-renewing trait (CSCs) via activation of PI3K/AKT and IL6/JAK2/STAT3 signaling pathways. We found that TrkB is a key regulator of PI3K/AKT and JAK/STAT signal pathway-mediated tumor metastasis and EMT program. Here, we demonstrated that TrkB activates AKT by directly binding to c-Src, leading to increased proliferation. Also, TrkB increases Twist-1 and Twist-2 expression through activation of JAK2/STAT3 by inducing c-Src-JAK2 complex formation. Furthermore, TrkB in the absence of c-Src binds directly to JAK2 and inhibits SOCS3-mediated JAK2 degradation, resulting in increased total JAK2 and STAT3 levels, which subsequently leads to JAK2/STAT3 activation and Twist-1 upregulation. Additionally, activation of the JAK2/STAT3 pathway via induction of IL-6 secretion by TrkB enables induction of activation of the EMT program via induction of STAT3 nuclear translocation. These observations suggest that TrkB is a promising target for future intervention strategies to prevent tumor metastasis, EMT program and self-renewing trait in breast cancer.     

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.     

DNA damage induces the IL-6/STAT3 signaling pathway, which has anti-senescence and growth-promoting functions in human tumors

IL-6 is a multifunctional cytokine that is important for immune responses, cell survival, apoptosis, and proliferation. However, little is known about the correlation between the IL-6 signaling pathway and DNA damage in human tumors. The present study demonstrates the role of the IL-6/STAT3 signaling pathway in human tumor cells exposed to DNA damage. Tumor cells exposed to DNA damage increase the expression and secretion of IL-6 and the phosphorylation of JAK1 and STAT3. The activation of the JAK1-STAT3 signaling pathway is inhibited by knockdown of gp130 or neutralization of soluble IL-6, implying that DNA damage induces the phosphorylation of JAK1 and STAT3 by autocrine IL-6. Interestingly, inhibition of the IL-6/STAT3 signaling pathway impairs the growth of tumor cells exposed to DNA damage and results in the induction of senescence. Therefore, the present study suggests that IL-6 inhibits senescence but promotes the survival and proliferation of tumor cells exposed to DNA damage through the activation of the JAK1-STAT3 signaling pathway.     

纳米二氧化钛对IEC-6细胞炎症因子表达及JAK2/STAT3蛋白磷酸化的影响

目的：探讨纳米二氧化钛（nano-TiO₂）对肠道上皮IEC-6细胞中炎症因子表达及Janus激酶2/信号传导及转录激活因子3（JAK2/STAT3）蛋白磷酸化的影响。方法：取对数生长期的IEC-6细胞,分别加入浓度为0.0（对照组）、5.0、10.0、15.0、20.0 μg/mL的nano-TiO₂培养24 h,采用噻唑蓝（MTT）比色法检测各组细胞存活率;酶联免疫吸附实验（ELISA）检测各组上清液中白介素-1β（IL-1β）、白介素-6（IL-6）和肿瘤坏死因子-α（TNF-α）水平;Western blot法测定各组细胞内JAK2和_STAT3蛋白表达及其磷酸化（p-JAK2和p-STAT3）水平;Image J软件分析蛋白条带灰度值。结果：nano-TiO₂处理组IEC-6细胞增殖活性与对照组相比差异无统计学意义（P>0.05）。与对照组相比,在各个nano-TiO₂处理浓度下,IEC-6细胞IL-6和TNF-α分泌水平均显著升高（P < 0.05）;10.0、15.0、20.0 μg/mL nano-TiO₂浓度处理后,细胞分泌IL-1β显著增加（P < 0.05）。Western blot法检测结果显示,nano-TiO₂处理组IEC-6细胞p-JAK2和p-STAT3蛋白表达升高,且其蛋白磷酸化水平和炎症因子表达水平呈正相关关系（r_JAK2,IL-1β=0.561,P < 0.05;r_JAK2,IL-6=0.711,P < 0.01;r_JAK2,TNF-α=0.675,P < 0.01;r_STAT3,IL-1β=0.782,P < 0.01;r_STAT3,IL-6=0.532,P < 0.05;r_STAT3,TNF-α=0.668,P < 0.01）。与对照组相比,15.0、20.0 μg/mL nano-TiO₂处理组IEC-6细胞中p-JAK2/JAK2和p-STAT3/STAT3灰度值比值明显升高（P < 0.05）。结论：nano-TiO₂可诱导IEC-6细胞分泌炎症因子和促进JAK2/STAT3蛋白磷酸化。     

Apoptosis in malignant glioma cells triggered by the temozolomide-induced DNA lesion O6-methylguanine

Methylating drugs such as temozolomide (TMZ) are widely used in the treatment of brain tumours (malignant gliomas). The mechanism of TMZ-induced glioma cell death is unknown. Here, we show that malignant glioma cells undergo apoptosis following treatment with the methylating agents N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and TMZ. Cell death determined by colony formation and apoptosis following methylation is greatly stimulated by p53. Transfection experiments with O(6)-methylguanine-DNA methyltransferase (MGMT) and depletion of MGMT by O(6)-benzylguanine showed that, in gliomas, the apoptotic signal originates from O(6)-methylguanine (O(6)MeG) and that repair of O(6)MeG by MGMT prevents apoptosis. We further demonstrate that O(6)MeG-triggered apoptosis requires Fas/CD95/Apo-1 receptor activation in p53 non-mutated glioma cells, whereas in p53 mutated gliomas the same DNA lesion triggers the mitochondrial apoptotic pathway. This occurs less effectively via Bcl-2 degradation and caspase-9, -2, -7 and -3 activation. O(6)MeG-triggered apoptosis in gliomas is a late response (occurring >120 h after treatment) that requires extensive cell proliferation. Stimulation of cell cycle progression by the Pasteurella multocida toxin promoted apoptosis whereas serum starvation attenuated it. O(6)MeG-induced apoptosis in glioma cells was preceded by the formation of DNA double-strand breaks (DSBs), as measured by gammaH2AX formation. Glioma cells mutated in DNA-PK(cs), which is involved in non-homologous end-joining, were more sensitive to TMZ-induced apoptosis, supporting the involvement of DSBs as a downstream apoptosis triggering lesion. Overall, the data demonstrate that cell death induced by TMZ in gliomas is due to apoptosis and that determinants of sensitivity of gliomas to TMZ are MGMT, p53, proliferation rate and DSB repair.     

丙泊酚抑制IL-6诱导的A549肺癌细胞上皮间质转化及其机制探讨

目的:探究丙泊酚对白细胞介素-6（IL-6）诱导的A549肺癌细胞上皮间质转化（EMT）的作用及机制。方法:将A549细胞随机分成四组:对照组、IL-6组（50 ng/ml重组IL-6蛋白）、IL-6+丙泊酚低剂量组（50 ng/ml重组IL-6蛋白和5 μmol/L丙泊酚）、IL-6+丙泊酚高剂量组（50 ng/ml重组IL-6蛋白和10 μmol/L丙泊酚）。MTT法检测细胞活力，Transwell检测细胞迁移情况，Real-time PCR方法检测EMT相关基因（E-cadherin、Vimentin和Snail1）mRNA的表达水平，Western blot检测EMT相关蛋白及JAK2和STAT3的磷酸化表达水平。使用0.5 μmol/L STAT3激活剂colivelin处理细胞，检测其对丙泊酚调节的IL-6诱导的A549细胞活力、迁移和EMT的影响。结果:与对照组相比，IL-6组中细胞的活力、迁移、EMT和JAK2/STAT3的活化均增加（P均<0.05）；与IL-6组相比，IL-6+丙泊酚组中细胞活力、迁移、EMT和JAK2/STAT3的活化均降低（P均<0.05），这些变化均具有剂量依赖性。STAT3激活剂能够减弱丙泊酚对IL-6诱导的A549细胞活力、迁移和EMT的影响（P均<0.05）。结论:丙泊酚能够抑制IL-6诱导的A549肺癌细胞EMT进程，这种作用是通过抑制JAK2/STAT3的活化发挥作用的。     

JAK/STAT信号转导途径活化和Mcl-1表达上调介导IL-6在人骨髓瘤细胞系XG-7上的凋亡抑制效应

背景和目的：IL－6能够抑制多种因素诱发的骨髓瘤细胞凋亡反应,在此过程中涉及到胞浆内一系列信号蛋白分子的参与。本研究旨在确定能够介导IL-6尖人骨髓瘤细胞系XG－7上凋亡抑制效应的Bcl-2家族抗凋亡蛋白（Bcl-2,Bcl-xL,Mcl-1)和IL－6信号转导途径（JAK／STAT,Ras,MAPK,PI-3K/Akt途径）。方法：采用碘化丙腚（PI）染色和流式细胞术分析XG－7细胞的凋亡情况;采用免疫印变方法检测Bcl-2家族分子在XG－7细胞中的表达情况;分别采用针对JAK／STAT,Ras/MAPK和PI－3K／Akt途径的特异性抑制剂AG490,PD98059和LY294002处理XG－7细胞,从而确定哪条信号转导途径能够介导IL－6在XG－7细胞上的凋亡抑制效应。结果：IL－6能够抑制XG－7细胞凋亡,同时上调Bcl-2家族抗凋亡蛋白Mcl-1表达。AG490处理的XG－7细胞中Mcl-1表达上调被明显抑制;但PD98059和LY294002处理后对Mcl-1表达没有显著影响。结论：IL－6在XG－7细胞上的凋抑制效应是通过上调Mcl-1表达和激活JAK／STAT途径而介导的,与Ras/MAPK和PI-3K/Akt途径的活化状态无关。     

The involvement of PI 3-K/Akt-dependent up-regulation of Mcl-1 in the prevention of apoptosis of Hep3B cells by interleukin-6

Interleukin-6 (IL-6) is a pleitrophic cytokine that not only regulates growth and differentiation of many cell types, but also induces production of acute phase proteins (AAP) in hepatocytes. Our previous works have demonstrated that both PI 3-K/Akt and STAT3 pathways were concomitantly activated and cooperatively mediated the anti-apoptotic effect of IL-6. This investigation reports that IL-6 protected cells against apoptosis induced by a variety of agents including, TGF-beta, UV and retinoic acid (RA) in Hep3B cells, suggesting that IL-6 is a fundamental determinant of hepatic cell survival. Mcl-1, but not other Bcl-2 family members, was rapidly up-regulated by IL-6, with a peak (approximately 3-4-fold) appearing at 4 h. Transient transfection of cells with a mcl-1 antisense vector, resulting in a 50-60% reduction of the anti-apoptotic effect of IL-6, indicating that Mcl-1 is a downstream effector of IL-6. Which signaling pathway transduced by IL-6 responsible for the Mcl-1 up-regulation was further investigated. In Hep3B cells, the JAK/STAT3, ERK, and PI 3-K/Akt pathways were activated by IL-6 stimulation. Blocking JAK/STAT3 activation with a dominant-negative mutant STAT3F or a JAK inhibitor AG490 could not influence IL-6-mediated Mcl-1 up-regulation. Similarly, PD98059 treatment, a MEK specific inhibitor, also failed to inhibit Mcl-1 expression. However, the IL-6-induced Mcl-1 up-regulation was effectively attenuated in the presence of PI 3-K inhibitors, LY294002 and wortmannin. Expression of dominant-negative Akt, but not Etk, could abrogate the IL-6-induced increase of Mcl-1. In conclusion, our results suggest that the anti-apoptotic effect of IL-6 is mediated, at least in part, by Mcl-1 expression and that is mainly through the PI 3-K/ Akt-dependent pathway.     

Mesenchymal stem cells enhance lung cancer initiation through activation of IL-6/JAK2/STAT3 pathway

Background

The role of mesenchymal stem cells (MSCs) and IL-6 in lung cancer has not been well-addressed. We aimed to determine if MSCs can enhance the ability of tumor initiation of lung cancer cells, and link MSCs with activation of the IL-6/JAK2/STAT3 signaling pathway.

Materials and methods

Lung cancer cell lines A549 and CL1-5 were directly or indirectly cocultured with MSCs. Spheres were defined as cell colonies with >50% area showing 3-dimensional structure and blurred cell margins. Cells without and with MSCs were injected into NOD/SCID mice. The percentage of tumor formation was determined. The influence of the IL-6/JAK2/STAT3 signaling pathway in cancer cell sphere formation and tumor growth were investigated.

Results

A very small number of lung cancer cells, when mixed with otherwise non-tumorigenic MSCs, obtained de novo tumorigenicity when injected subcutaneously and allowed to form a tumor xenograft. Secretion of IL-6 from MSCs increased activation of the JAK2/STAT3 pathway in cancer cells, and enhanced sphere formation and tumor initiation. A reduced capacity of tumor formation of A549 and CL1-5 lung cancer cells when IL-6 was inhibited in MSCs or STAT3 was silenced in A549 and CL1-5 admixed with MSCs.

Conclusions

Culture of A549 or CL1-5 lung cancer cells with MSCs increased sphere formation, drug resistance, and overexpression of pluripotency markers through activation of the IL-6/JAK2/STAT3 pathway. MSCs enhanced the capability of A549 and CL1-5 lung cancer cells to form tumors in immunodeficient mice. Blockade of the IL-6/JAK2/STAT3 pathway attenuated the capability of A549 and CL1-5 cells to form tumors.     

Epigenetic regulation of glial fibrillary acidic protein by DNA methylation in human malignant gliomas

Glial fibrillary acidic protein (GFAP) is an intermediate filament expressed in glial cells that stabilizes and maintains the cytoskeleton of normal astrocytes. In glial tumors, GFAP expression is frequently lost with increasing grade of malignancy, suggesting that GFAP is important for maintaining glial cell morphology or regulating astrocytoma cell growth. Most permanent human glioma cell lines are GFAP negative by immunocytochemistry. Given that the GFAP gene is not mutated in human glioma specimens or glioma cell lines, we considered epigenetic mechanisms, such as promoter methylation, as a cause of silencing of GFAP in these tumors. In this study, we treated known GFAP-negative glioma cell lines with 5-aza-2'-deoxycytidine to examine GFAP promoter hypermethylation. Additionally, we performed bisulfite sequencing on primary glioma samples and glioma cell lines and showed an inverse relationship between GFAP promoter methylation status and GFAP expression. Using a gene reporter assay with the GFAP promoter cloned upstream of a luciferase gene, we showed that methylation of the GFAP promoter downregulates the expression of the luciferase gene. Our results suggest that epigenetic silencing of the GFAP gene through DNA methylation of its promoter region may be one mechanism by which GFAP is downregulated in human gliomas and glioma cell lines.