Knockdown Of STAT3 Expression Research Articles

Endothelial Stat3 activation promotes osteoarthritis development.

The mechanism of the balance between subchondral angiogenesis and articular damage within osteoarthritis (OA) progression remains a mystery. However, the lack of specific drugs leads to limited clinical treatment options for OA, frequently failing to prevent eventual joint destruction in patients. Increasing evidence suggests that subchondral bone angiogenesis precedes cartilage injury, while proliferating endothelial cells (ECs) induce abnormal bone formation. Signal transducer and activator of transcription 3 (Stat3) is triggered by multiple cytokines in the OA microenvironment. Here, we observed elevated Stat3 activation in subchondral bone H-type vessels. Endothelial Stat3 activation will lead to stronger cell proliferation, migration and angiogenesis by simulating ECs in OA. In contrast, either Stat3 activation inhibition or knockdown of Stat3 expression could relieve such alterations. More interestingly, blocking Stat3 in ECs alleviated angiogenesis-mediated osteogenic differentiation and chondrocyte lesions. Stat3 inhibitor reversed surgically induced subchondral bone H-type vessel hyperplasia in vivo, significantly downregulating vessel volume and vessel number. Due to the reduced angiogenesis, subchondral bone deterioration and cartilage loss were alleviated. Overall, our data suggest that endothelial Stat3 activation is an essential trigger for OA development. Therefore, targeted Stat3 blockade is a novel promising therapeutic regimen for OA.

The potential role of STAT3 In the APE1/NF-kB regulatory axis in K-rasLSL.G12D/+;Pdx-1-Cre (KC) pancreatic tumor model

APE1/Ref-1 (apurinic/apyrimidinic endonuclease-redox effector factor 1) is a multifunctional protein that has been shown to be overexpressed in multiple types of cancer. The overexpression of APE1/Ref-1 is linked to higher cancer cell survival and increased patient mortality. Furthermore, APE1/Ref-1 is a key regulator of transcription factors (TF) through redox signaling and protein-protein interaction. It is involved in proliferative and inflammatory signaling upregulated in cancer. 
 Transcription factor NF-kB is involved in inflammatory cytokine expression and has been shown to be regulated by Ref-1. My project investigated how Ref-1 regulates NF-kB, specifically Rel-A, in a model using K-rasLSL.G12D/+; Pdx-1-Cre (KC) pancreatic tumor cells (KC3590) derived from genetically engineered mice. Additionally, I explored other TFs within the APE1/Ref-1 signaling pathway, such as STAT3, in this model. 
 My work involved knocking down STAT3 levels within four variations of the KC3590 line. These were the KC3590/ΔNF-kB (parent) and KC3590/ΔNF-kB vector lines (vector) which contain exon deletions within the NF-kB gene rendering it nonfunctional. KC3590/13 and KC3590/15 are cell lines which are KC3590/ΔNF-B cells with functional full-length NF-kB added to the cells. Previous experiments demonstrated that the ΔNF-kB and ΔNF-kB vector lines are resistant to treatment by the specific Ref-1 inhibitors, including APX3330, which inhibit the redox signaling function of Ref-1. 
 Initial data demonstrated that adding back functional NF-kB to the NF-kB deficient cells reestablished sensitivity to APX3330, presumably due to the reintroduction of the Ref-1 target, NF-kB. Knockdown of STAT3 expression in the ΔNF-kB and ΔNF-kB vector lines demonstrated some sensitivity to APX3330, however, in the C13/15 cell lines, no enhanced sensitivity was observed. These data support the hypothesis that NF-kB is the major TF driving the growth of KC pancreatic tumor cells. Subsequent studies will clarify further the role of APE1/Ref-1 regulation in the KC model and the relative importance of APE1/Ref-1’s target TFs.

Inhibition of STAT3 enhances sensitivity to tamoxifen in tamoxifen-resistant breast cancer cells

BackgroundThe mechanisms of endocrine resistance are complex, and deregulation of several oncogenic signalling pathways has been proposed. We aimed to investigate the role of the EGFR and Src-mediated STAT3 signalling pathway in tamoxifen-resistant breast cancer cells.MethodsThe ER-positive luminal breast cancer cell lines, MCF-7 and T47D, were used. We have established an MCF-7-derived tamoxifen-resistant cell line (TamR) by long-term culture of MCF-7 cells with 4-hydroxytamoxifen. Cell viability was determined using an MTT assay, and protein expression levels were determined using western blot. Cell cycle and annexin V staining were analysed using flow cytometry.ResultsTamR cells showed decreased expression of estrogen receptor and increased expression of EGFR. TamR cells showed an acceleration of the G1 to S phase transition. The protein expression levels of phosphorylated Src, EGFR (Y845), and STAT3 was increased in TamR cells, while phosphorylated Akt was decreased. The expression of p-STAT3 was enhanced according to exposure time of tamoxifen in T47D cells, suggesting that activation of STAT3 can cause tamoxifen resistance in ER-positive breast cancer cells. Both dasatinib (Src inhibitor) and stattic (STAT3 inhibitor) inhibited cell proliferation and induced apoptosis in TamR cells. However, stattic showed a much stronger effect than dasatinib. Knockdown of STAT3 expression by siRNA had no effect on sensitivity to tamoxifen in MCF-7 cells, while that enhanced sensitivity to tamoxifen in TamR cells. There was not a significant synergistic effect of dasatinib and stattic on cell survival. TamR cells have low nuclear p21(Cip1) expression compared to MCF-7 cells and inhibition of STAT3 increased the expression of nuclear p21(Cip1) in TamR cells.ConclusionsThe EGFR and Src-mediated STAT3 signalling pathway is activated in TamR cells, and inhibition of STAT3 may be a potential target in tamoxifen-resistant breast cancer. An increase in nuclear p21(Cip1) may be a key step in STAT3 inhibitor-induced cell death in TamR cells.

Vagus nerve stimulation enhances the cholinergic anti-inflammatory pathway to reduce lung injury in acute respiratory distress syndrome via STAT3

The cholinergic anti-inflammatory pathway (CAIP) is important for antagonizing inflammation and treating several diseases, including acute respiratory distress syndrome (ARDS), and is related to vagus nerve integrity. However, its underlying pathophysiological mechanism is still unclear. We hypothesized that CAIP regulates lung injury repair after ARDS through the STAT3 signaling pathway, which is an important downstream effector of α7nAchR. We enhanced CAIP activity by subjecting rats to vagus nerve stimulation (VNS), and administered the α-7 acetylcholine receptor (α7nAchR) agonist and antagonist to determine whether VNS can reduce lung injury by regulating the pulmonary inflammatory response through CAIP. After being subjected to VNS, the secretion of TNF-α and IL-1β was decreased, while the level of IL-10 was increased in the rat model of ARDS. Moreover, VNS treatment reduced lung mRNA levels of M1 macrophage markers, while increased those of M2 macrophage markers. The expression of Caspase-1 decreased, while that of STAT3 increased in lung tissue after VNS treatment. The aforementioned effects of VNS were reversed by cutting the cervical vagus efferent branch and blocking α7nAchR. These findings suggest that VNS inhibits the ARDS inflammatory response by promoting CAIP activity. Next, we used lentivirus knockdown of STAT3 expression to explore the mechanism of VNS through CAIP on lung inflammation in ARDS model rats. VNS activates α7nAchR, increases STAT3 expression, reduces Caspase-1 expression, suppresses inflammation by inhibiting inflammatory pyroptosis and M1 to M2 macrophage transformation, which may constitute the main mechanism of VNS action in ARDS.

Human omental adipose-derived mesenchymal stem cells enhance autophagy in ovarian carcinoma cells through the STAT3 signalling pathway

BackgroundOur previous study showed that human omental adipose-derived stem cells (ADSCs) promote ovarian cancer growth and metastasis. In this study, the role of autophagy in the ovarian cancer-promoting effects of omental ADSCs was further determined. MethodsThe growth and invasion of ovarian cancer cells were detected by CCK-8 and Transwell assays, respectively. The autophagy of ovarian cancer cells transfected with MRFP-GFP-LC3 adenoviral vectors was evaluated by confocal microscopy and western blot assay. Transfection of STAT3 siRNA was used to inhibit the expression of STAT3. ResultsOur results show that autophagy plays a vital role in ovarian cancer and is promoted by ADSCs. Specifically, we show that proliferation and invasion are correlated with autophagy induction by ADSCs in two ovarian cancer cell lines under hypoxic conditions. Mechanistically, ADSCs activate the STAT3 signalling pathway, thereby promoting autophagy. Knockdown of STAT3 expression using siRNA decreased hypoxia-induced autophagy and decreased the proliferation and metastasis of ovarian cancer cells. ConclusionTaken together, our data indicate that STAT3-mediated autophagy induced by ADSCs promotes ovarian cancer growth and metastasis.

Abstract 5872: Stat3 feedback activation-induced PTGIS expression is associated with acquired resistance to EGFR-TKI in lung cancer

Abstract Targeted cancer therapies can effectively promote tumor regression in clinical responses. Eventually, most tumors develop resistance to these drugs. Stat3 activation has been suggested as one of the mechanisms that cause acquired resistance to EGFR-tyrosin kinase inhibitor (TKI) in non-small cell lung cancer (NSCLC). However, the underlying molecular mechanisms are not well studied. In this study, we found that treatment of gefitinib (EGFR-TKI) in NSCLC cell lines harboring EGFR-TKI sensitive mutation induced feedback activation of Stat3 in a time- and dose-dependent manner. High levels of IL-6 were detected in the conditioned medium of gefitinib-treated cells by cytokine array and were confirmed by ELISA. We demonstrated that IL-6 treatment could induce Stat3 activation and conditioned medium treatment-induced Stat3 activation was suppressed by IL-6 neutralizing antibody. We also demonstrated that gefitinib treatment-induced IL-6 secretion could be inhibited by knockdown of Stat3 expression. Moreover, pharmacological inhibition and genetic inhibition of Stat3 activation increased cell cytotoxicity of gefitinib in both PC9 and HCC827 cells that harboring EGFR-TKI sensitive mutation. Our data suggested that gefitinib treatment could induce activation of IL-6/Stat3 signaling loop and modulate cell cytotoxicity of gefitinib. Microarray and Ingenuity Pathway Analysis (IPA) analysis revealed prostaglandin I2 synthase (PTGIS) as a downstream target gene of IL-6/Stat3 signaling and PTGIS was up-regulated by gefitinib treatment. The induction of PTGIS by gefitinib via Stat3 feedback activation was confirmed in vitro genetically and pharmacologically. Moreover, we showed that cotreatment with PTGIS inhibitor improves the efficacy of EGFR inhibition in PC9 and HCC827 cells. Importantly, high expression of PTGIS was found in gefitinib-resistant PC9 cells (PC9/gef) compared with gefitinib-sensitive PC9 cells. Targeting PTGIS was also effective in decreasing viability of cells with acquired resistance to gefitinib in PC9/gef cells. Taken together, our study indicated that Stat3 feedback activation-induced PTGIS expression participates in modulating gefitinib efficacy and Stat3/PTGIS inhibition could potentially overcome acquired resistance to gefitinib in NSCLC. Note: This abstract was not presented at the meeting. Citation Format: Hsuan-Heng Yeh, Shang-Yin Wu, Chun-Hua Hung, Wu-Chou Su. Stat3 feedback activation-induced PTGIS expression is associated with acquired resistance to EGFR-TKI in lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5872. doi:10.1158/1538-7445.AM2017-5872

Bone marrow endothelium-targeted therapeutics for metastatic breast cancer

Effective treatment of cancer metastasis to the bone relies on bone marrow drug accumulation. The surface proteins in the bone marrow vascular endothelium provide docking sites for targeted drug delivery. We have developed a thioaptamer that specifically binds to E-selectin that is overexpressed in the vasculature of tumor and inflammatory tissues. In this study, we tested targeted delivery of therapeutic siRNA loaded in the E-selectin thioaptamer-conjugated multistage vector (ESTA-MSV) drug carrier to bone marrow for the treatment of breast cancer bone metastasis. We evaluated tumor type- and tumor growth stage-dependent targeting in mice bearing metastatic breast cancer in the bone, and carried out studies to identify factors that determine targeting efficiency. In a subsequent study, we delivered siRNA to knock down expression of the human STAT3 gene in murine xenograft models of human MDA-MB-231 breast tumor, and assessed therapeutic efficacy. Our studies revealed that the CD31+E-selectin+ population accounted for 20.8%, 26.4% and 29.9% of total endothelial cells respectively inside the femur of mice bearing early, middle and late stage metastatic MDA-MB-231 tumors. In comparison, the double positive cells remained at a basal level in mice with early stage MCF-7 tumors, and jumped to 23.9% and 28.2% when tumor growth progressed to middle and late stages. Accumulation of ESTA-MSV inside the bone marrow correlated with the E-selectin expression pattern. There was up to 5-fold enrichment of the targeted MSV in the bone marrow of mice bearing early or late stage MDA-MB-231 tumors and of mice with late stage, but not early stage, MCF-7 tumors. Targeted delivery of STAT3 siRNA in ESTA-MSV resulted in knockdown of STAT3 expression in 48.7% of cancer cells inside the bone marrow. Weekly systemic administration of ESTA-MSV/STAT3 siRNA significantly extended survival of mice with MDA-MB-231 bone metastasis. In conclusion, targeting the overexpressed E-selectin provides an effective approach for tissue-specific drug delivery to the bone marrow. Tumor growth in the bone can be effectively inhibited by blockage of the STAT3 signaling.

Abstract A253: HO-3867, a safe STAT3 inhibitor, is selectively cytotoxic to ovarian cancer.

Abstract We have developed a novel class of bi-functional compounds based on a diarylidenyl-piperidone (DAP) backbone conjugated to an N-hydroxypyrroline (-NOH; a nitroxide precursor) group which selectively inhibits STAT3 activation, translocation, and DNA binding activity, without affecting the expression of other pSTATs. This new STAT3 inhibitor offers advantages when compared to other STAT3-targeting molecules currently available, under development or undergoing preclinical trials. Most notably, these compounds exhibit minimal toxicity toward normal cells and tissues while inducing apoptosis in ovarian cancer cells, and exhibit good oral bioavailability. Results show that selective cytotoxicity of the lead compound, HO-3867, towards cancer cells is multi-faceted. AutoDock molecular modeling indicates that the DAP compounds interact with STAT3 at the DNA-binding domain. Liquid chromatography / Mass spectroscopy analysis demonstrates greater bioabsorption and bioavailability of active (cytotoxic) metabolites in cancer cells when compared to normal cells. Differential activation of the Akt pathway was demonstrated using Akt siRNA in normal versus cancer cells. Knockdown of STAT3 expression using two different shRNAs shows the requirement of STAT3 for HO-3867-mediated apoptosis. In vivo testing shows that HO-3867 inhibits xenograft tumor growth without toxic side effects. In addition, HO-3867 significantly inhibited cell survival, migration/invasion and induced cell death in primary ovarian cancer cell populations isolated from ascites of patients with recurrent and advanced ovarian cancer. This study provides evidence of a safe, targeted STAT3 inhibitor (HO-3867) with demonstrated efficacy in treating multiple ovarian cancer models. This suggests significant translational potential of these compounds for the treatment of ovarian cancer. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A253. Citation Format: Karuppaiyah Selvendiran, Kellie S. Rath, Shan Naidu, Pushpa Latha, Bid Hemant, Georgia A. McCann, Veronica Bravo, Peter Houghton, Gustavo Leone, Kálmán Hideg, Periannan Kuppusamy, David E. Cohn. HO-3867, a safe STAT3 inhibitor, is selectively cytotoxic to ovarian cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A253.

Abstract 878: Tanshinone-1 kills multidrug resistant tumor cells via reducing phospho-705-Stat3, potentiated by inhibiting secondary activation of signaling networks.

Abstract One of the severest hurdles in cancer treatment is multidrug resistance (MDR), resulting from overexpression of drug transporters and/or deregulation of cellular signaling transduction. Persistent efforts have been made to find new agents and strategies to overcome MDR. MDR involves almost all clinically-used anticancer drugs with natural origins. In this study, however, we found that the natural product tanshinone-1 could circumvent MDR via reducing phospho-705-Stat3, potentiated by inhibiting secondary activation of signaling networks. Tanshinone-1 is a bioactive ingredient in traditional Chinese medicine that exhibits diverse biologic properties, including anticancer properties. Tanshinone-1 displayed equipotent or even more potent cytotoxicity in three MDR tumor cell lines than in their corresponding parental cell lines. Tanshinone-1 induced apoptosis of the MDR cells by activating the intrinsic apoptotic pathway via disturbing mitochondria membrane potential and eliciting the cleavage of caspase-9 and caspase-3. The killing of MDR cells by tanshinone-1 was independent of drug transporters, but correlated tightly with its decreasing phospho-705-Stat3, highly possibly via activating certain phosphatase(s). The expression of the target genes of Stat3 including Mcl-1, cyclin D1, cIAP-2 and c-myc, was downregulated by the treatment with tanshinone-1. Knockdown of stat3 expression with specific small interfering RNA led to reduced sensitivity of the tested MDR cells to tanshinone-1. Treatment with Na3VO4, a pan inhibitor of phosphatases, completely reversed tanshinone-1-induced decrease of phospho-705-Stat3 and significantly lowered its cytotoxicity. Knockdown of phosphatase SHP-2 or PTP1B prevented reduction of phospho-705-Stat3 and induction of cell apoptosis driven by tanshinone-1. Further investigation revealed that tanshinone-1 activated signaling networks involving Akt, p38 and Erk pathways, possibly secondary to its reducing phospho-705-Stat3. Notably, simultaneous suppression of those pathways enhanced the cytotoxic effect of tanshinone-1 against the tested MDR cells. Cotreatment of the PI3K inhibitor PI103, the p38 inhibitor SB203580 and/or the MEK inhibitor AZD6244 with tanshinone-1 potentiated its apoptotic induction. However, PI103 and SB580203 appeared to show more potent synergism than AZD6244 when combined with tanshinone-1. Together, this study presents tanshinone-1 as an MDR-overcoming natural product, and more importantly, from our results, a therapeutic strategy of targeting signaling network(s) may evolve for MDR cancer therapy. Citation Format: Lei Xu, Jian-Ming Feng, Jia-Xin Li, Jin-Mei Zhu, Shan-Shan Song, Lin-Jiang Tong, Yi Chen, Fu-Lin Lian, Dong-Hai Lin, Jian Ding, Ze-Hong Miao. Tanshinone-1 kills multidrug resistant tumor cells via reducing phospho-705-Stat3, potentiated by inhibiting secondary activation of signaling networks. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 878. doi:10.1158/1538-7445.AM2013-878

Curcumin Blocks Small Cell Lung Cancer Cells Migration, Invasion, Angiogenesis, Cell Cycle and Neoplasia through Janus Kinase-STAT3 Signalling Pathway

Curcumin, the active component of turmeric, has been shown to protect against carcinogenesis and prevent tumor development. However, little is known about its anti-tumor mechanism in small cell lung cancer (SCLC). In this study, we found that curcumin can inhibit SCLC cell proliferation, cell cycle, migration, invasion and angiogenesis through suppression of the STAT3. SCLC cells were treated with curcumin (15 µmol/L) and the results showed that curcumin was effective in inhibiting STAT3 phosphorylation to downregulate of an array of STAT3 downstream targets ,which contributed to suppression of cell proliferation, loss of colony formation, depression of cell migration and invasion. Curcumin also suppressed the expression of proliferative proteins (Survivin, Bcl-XL and Cyclin B1), and invasive proteins (VEGF, MMP-2, MMP-7 and ICAM-1).Knockdown of STAT3 expression by siRNA was able to induce anti-invasive effects in vitro. In contrast, activation of STAT3 upstream of interleukin 6 (IL-6) leads to the increased cell proliferation ,cell survival, angiogenesis, invasion, migration and tumor growth. Our findings illustrate the biologic significance of IL-6/JAK/STAT3 signaling in SCLC progression and providenovel evidence that the pathway may be a new potential target for therapy of SCLC. It was concluded that curcumin is a potent agent in the inhibition of STAT3 with favorable pharmacological activity,and curcumin may have translational potential as an effective cancer therapeutic or preventive agent for SCLC.

Knockdown of stat3 expression by RNAi inhibits in vitro growth of human ovarian cancer

BackgroundThe aim of the study was to investigate the suppressive effects of pSilencer2.1-U6-siRNA-stat3 recombinant plasmids on the growth of ovarian cancer in vitro.Material and methods.Three pairs of DNA template (stat3-1, stat3-2, stat3-3) specific for different target sites on stat3 mRNA were synthesized to reconstruct pSilencer2.1-U6-siRNA-stat3s, which were transfected into SKOV3 cells. The expressions of STAT3, BcL-2, cyclin D1 and C-myc in these cells were detected by Western blot and Northern blot. The cell cycle and the growth were determined by flow cytometry (FCM) and MTT assay, respectively. Cell apoptosis was determined by TUNEL staining.ResultsOf the three siRNAs, only siRNA targeting stat3-3 markedly suppressed the protein expression of stat3 in SKOV3 cells; MTT assay and FCM showed that transfection of stat3-3 siRNA could significantly suppress the growth of SKOV3 cells and arrest the cell cycle in vitro. TUNEL staining also showed massive apoptosis in SKOV3 cells transfected with stat3-3 siRNA.ConclusionspSilencer2.1-U6-siRNA-stat3-3 can significantly inhibit the STAT3 expression in human ovarian cancer cells resulting in the inhibition of the cancer growth and the increase of apoptosis of cancer cells.

Abstract PD03-09: Metformin Induces Apoptosis in Triple Negative Breast Cancer Cells Via Inhibition of Stat3 Activity

Abstract Background: Metformin inhibits breast cancer cell proliferation and colony formation, with S phase arrest and the induction of apoptosis in triple negative breast cancer cells in vitro. In these cells, metformin down-regulates Cyclin D1 and Cyclin E, as well as EGFR, p-EGFR, p-AKT, p-MAPK, p-Src and p-mTOR, whereas it up-regulates p-AMPK (Liu, et al. Cell Cycle, 2009). Non-triple negative breast cancer cells are resistant to metformin induced apoptosis, although they show similar changes in p-AMPK induction with metformin (Alimova, et al. Cell Cycle, 2009). We hypothesized that there are unique signaling intermediates associated with metformin responsivity in triple negative cells and have identified the signal transducer and activator of transcription 3 (Stat3) as a potential target. Stat3 is constitutively activated in a wide range of tumors, including breast cancer (up to 60%). It reportedly promotes cancer cell proliferation and survival. Methods: Human triple negative breast cancer cell lines (MDA-468, MDA-231, BT20 and HCC70) were used to evaluate interactions between metformin and Stat3 signaling. Activation of Stat3 was examined by Western blot analysis with phosphorylation-specific antibodies. Cell proliferation was determined by MTS assay. Apoptosis was quantitated by an apoptosis ELISA assay and Western blots for PARP and caspase cleavage. In these 4 cell lines, Stat3-over-expressing clones were obtained via transfection of a constitutive active (CA) construct of Stat3. Specific knock-down of Stat3 expression was achieved by using a lentiviral system containing Stat3 small hairpin RNA. Results: In a dose and time dependent manner, metformin inhibits Stat3 phosphorylation at sites Tyr705 and Ser727, Cyclin D1 and E protein expression, cleavage of PARP and the pro-caspases 3, 8, and 9. Overexpression of the CA-Stat3 attenuates the aforementioned meformin-associated PARP and caspase cleavage as well as apoptosis, and it suppresses metformin induced cell cycle arrest and changes in cyclin D1 and E. In contrast, specific knock-down of Stat3 expression sensitizes the triple negative breast cancer cells to metformin-mediated apoptosis and cell cycle arrest, enhancing the signaling changes we describe above. Conclusion: These data indicate that Stat3 is a critical intermediary for metformin action in triple negative breast cancer cells. Our studies suggest that targeting Stat3 activation may be a useful strategy to treat breast cancer patients with triple negative phenotype. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr PD03-09.

Knockdown of STAT3 expression by RNAi suppresses growth and induces apoptosis and differentiation in glioblastoma stem cells

Glioblastoma is a highly lethal brain tumor of the human primary nervous system tumors. Previous studies demonstrated that glioblastoma stem cells were able to initiate and reform the original cancer. In this study, we found that there were expression and activation of STAT3, a key signal transduction factor and oncoprotein, in human glioblastoma stem cells (GSCs). STAT3 plays a key role in proliferation, apoptosis and differentiation in embryonic stem cells and several cancer types. To investigate the effects of STAT3 on human GSCs, the expression and activation of STAT3 were suppressed by RNAi mediated with lentivirus. We demonstrated that siRNA of STAT3 significantly suppressed STAT3 expression and activation and resulted in inhibition of cell growth in GSCs. Knockdown of STAT3 induces apoptosis and reduces significantly expression of Bcl-2 and cyclin-D in human primary GSCs, whereas no significance was achieved in BAX and caspase-3 expression. Inhibition of STAT3 expression is associated not only with decreasing of CD133+ cell proportion and increasing of GFAP and MBP expression, but also with decrease of the capacity to initiate a tumor in human primary GSCs. Together, these studies suggest that STAT3 is an important target for human GSCs in regulation of GSCs growth, apoptosis, differentiation and tumorigenic potential.

Stat3-siRNA induces Fas-mediated apoptosis in vitro and in vivo in breast cancer

Stat3, a member of the signal transducer and activator of transcription family, has the potential to mediate cell survival, growth and differentiation. Stat3 is constitutively activated in numerous cancers, including >50% of breast cancers. Previous studies demonstrated that constitutively activated Stat3 plays an important role in breast cancer development and progression by promoting cell proliferation and inhibiting apoptosis. The present study was designed to investigate the potential use of RNA interference (RNAi) to block Stat3 expression and activation, as well as the subsequent effect on human breast cancer cell growth. Our studies show that knockdown of STAT3 expression by siRNA reduced expression of Bcl-xL and survivin in MDA-MB-231 cells, and also led to Fas mediated intrinsic apoptotic pathway by activating caspases -8, -9, -3 and PARP1 cleavage. In nude mice, pRNAi-Stat3 significantly suppressed tumor growth compared with controls. It also suppressed Stat3 expression, and downregulated BcL-xL and upregulated Fas, Fas-L and cleaved caspase-3 expression within the tumor, which significantly induced apoptosis and led to tumor suppression. Thus, targeting Stat3 signaling using siRNA may serve as a novel therapeutic strategy for the treatment of breast cancers expressing constitutively activated Stat3.

STAT3 tyrosine phosphorylation is critical for interleukin 1 beta and interleukin-6 production in response to lipopolysaccharide and live bacteria

Both interleukin 1 beta (IL-1β) and interleukin-6 (IL-6) are pro-inflammatory cytokines that play a major role in inflammatory diseases as well as cancer. In this work we investigated the signaling pathway involving lipopolysaccharide (LPS)-mediated IL-1β and IL-6 production in murine macrophage cell lines and primary macrophages. We show that in response to LPS, the JAK/STAT pathway is activated, leading to tyrosine phosphorylation at residue 705 on STAT3 and at residue 701 on STAT1, respectively. A newly developed STAT3 specific inhibitor (stattic) blocked LPS-mediated STAT3 tyrosine phosphorylation and led to inhibition of LPS-mediated IL-1β and IL-6 production but not TNF-α production. Knockdown of STAT3 expression via small interfering RNA (siRNA) decreased the level of STAT3 expression in Raw 264.7 cells and decreased STAT3 tyrosine phosphorylation in response to LPS treatment. Quantitative real time PCR and Western analysis of cells treated with inhibitor or STAT3 siRNA after LPS treatment showed a significant reduction of IL-1β and IL-6 mRNA and protein compared to cells treated with LPS alone. Moreover stattic abrogated IL-1β formation in response to extracellular bacteria Staphylococcus aureus and Escherichia coli in murine peritoneal macrophages. This inhibition did not affect caspase-1 activation. These results highlight the complex role of STAT3 in cytokine production and the key role of STAT3 tyrosine phosphorylation in IL-1β and IL-6 production in response to inflammation.

CNTF induces photoreceptor neuroprotection and Müller glial cell proliferation through two different signaling pathways in the adult zebrafish retina

Ciliary neurotrophic factor (CNTF) acts in several processes in the vertebrate retina, including neuroprotection of photoreceptors in the stressed adult retina and regulation of neuronal progenitor cell proliferation during retinal development. However, the signaling pathway it utilizes (Jak/Stat, MAPK, or Akt) in these processes is ambiguous. Because dark-adapted albino zebrafish exhibit light-induced rod and cone cell death and subsequently regenerate the lost photoreceptor cells, zebrafish should be a useful model to study the role of CNTF in both neuroprotection and neuronal progenitor cell proliferation. We therefore investigated the potential roles of CNTF in both the undamaged and light-damaged adult zebrafish retinas. Intraocular injection of CNTF suppressed light-induced photoreceptor cell death, which then failed to exhibit the regeneration response that is marked by proliferating Müller glia and neuronal progenitor cells. Inhibiting the MAPK signaling pathway, but neither the Stat3 nor Akt pathways, significantly reduced the CNTF-mediated neuroprotection of light-induced photoreceptor cell death. Intraocular injection of CNTF into non-light-treated (undamaged) eyes mimicked constant intense light treatment by increasing Stat3 expression in Müller glia followed by increasing the number of proliferating Müller glia and neuronal progenitors. Knockdown of Stat3 expression in the CNTF-injected non-light-treated retinas significantly reduced the number of proliferating Müller glia, while coinjection of CNTF with either MAPK or Akt inhibitors did not inhibit the CNTF-induced Müller glia proliferation. Thus, CNTF utilizes a MAPK-dependant signaling pathway in neuroprotection of light-induced photoreceptor cell death and a Stat3-dependant signaling pathway to stimulate Müller glia proliferation.

STAT3 silencing with lentivirus inhibits growth and induces apoptosis and differentiation of U251 cells

Glioblastoma multiforme (GBM), the most common type of central nervous system tumor in humans, is highly proliferative and resistant to apoptosis associated with genetic mutations that deregulate cell cycle. Signal transduction and activation of transcription 3 (Stat3) is a key signal transduction protein that mediated signaling by cytokines and contributed to oncogenesis. It is constitutively activated in numerous cancers including glioblastoma. To determine the effect on proliferation and differentiation of glioblastoma U251 cells after inhibiting STAT3 expression by RNAi, STAT3 gene was silenced with lentivirus vector in U251 cells. We demonstrate that a lentivirus-based shRNA vector had highly infecting efficiency to U251 cells and lentivirus vector-mediated RNAi significantly suppressed Stat3 expression and activation in U251 cells. Knockdown of STAT3 expression by RNAi suppressed the growth and induced apoptosis of U251 cells by down-regulating expression of Bcl-2. It was found that the cell proportion of G0/G1 phase significantly increased after silencing Stat3 by down-regulating expression of cyclin D1. Knockdown of Stat3 also induces morphological changes of U251 cell. It increases significantly expression of myelin basic protein (MBP) in U251 cells. This study demonstrates that STAT3 silencing with lentivirus effectively inhibits STAT3 gene expression and activation. Stat3 is associated with the survival, growth and differentiation of U251 cells. Lentivirus vector-mediated RNAi may be serve as a novel therapeutic strategy for treatment of GBM with expression constitutively and activation of STAT3 gene.

PDGF-induced human airway smooth muscle cell proliferation requires STAT3 and the small GTPase Rac1

The signal transducers and activators of transcription (STAT) family of transcription factors regulates a variety of biological functions including cellular proliferation, transformation, apoptosis, and differentiation. We have previously determined that PDGF activates the STAT pathway in human airway smooth muscle cells (HASMC) and that the Jak and Src kinases are required for both PDGF-induced STAT activation and HASMC proliferation. As increased airway smooth muscle (ASM) volume is associated with airflow obstruction and disease severity in patients with asthma, it is important to elucidate the cellular and molecular pathways that regulate ASM accumulation. In this paper, we investigated the requirement of STAT3 for PDGF-induced HASMC proliferation. We demonstrate that knockdown of STAT3 expression in HASMC resulted in a significant decrease in mitogen-induced cellular proliferation. Additionally, PDGF-induced activation of STAT3 required the small GTP-binding protein Rac1, and Rac1 was also required for PDGF-induced HASMC proliferation. Furthermore, PDGF treatment induced STAT3 and Rac1 to physically associate and translocate to the nucleus, identifying one mechanism by which STAT3 is regulated in response to PDGF in HASMC. Finally, we determined that STAT3 expression is required for PDGF-mediated regulation of cell cycle targets cyclin D3 and p27. These data define a novel mitogenic signaling pathway in airway smooth muscle cells leading from PDGF to Rac1 and STAT3 and subsequent cell cycle gene regulation. Thus, targeting STAT3 may prove to be a novel therapeutic approach for patients with severe asthma and significant airway wall remodeling, as manifested by ASM accumulation.

Hypothalamic Apolipoprotein A-IV Is Regulated by Leptin

Apolipoprotein A-IV (apo A-IV) is a satiety factor involved in the control of food intake and body weight. Our previous studies demonstrated that apo A-IV is present in areas of the hypothalamus where leptin acts to influence energy homeostasis. In the present studies, we found that leptin-deficient obese (ob/ob) mice have significantly reduced hypothalamic apo A-IV mRNA levels. Intragastric infusion of a lipid emulsion significantly stimulated hypothalamic apo A-IV gene expression in lean controls but not in ob/ob mice. Daily ip administration of leptin (3 microg/g) for 5 d significantly increased hypothalamic apo A-IV mRNA levels of ob/ob mice relative to pair-fed controls. In addition, centrally administered leptin raised the reduced apo A-IV gene expression induced by fasting. Using immunohistochemistry, we demonstrated that apo A-IV is present in leptin-sensitive phosphorylated signal transducer and activator of transcription 3 (pSTAT3)-positive cells of the arcuate nucleus of the hypothalamus. Knockdown of STAT3 expression by small interfering RNA significantly attenuated the stimulatory effect of leptin on apo A-IV protein expression in cultured primary hypothalamic neurons, implying that the hypothalamic apo A-IV is regulated by leptin, at least partially, via the STAT3 signaling pathway. Third-ventricular (intracerebroventricular) administration of a subthreshold dose of leptin (1 microg) potentiated apo A-IV-induced (subthreshold dose, 0.5 microg) reduction of feeding, indicating the existence of a functional synergistic interaction between leptin and apo A-IV, leading to suppression of food intake.

Knockdown of Stat3 in C17.2 neural stem cells facilitates the generation of neurons: a possibility of transplantation with a low level of oncogene

This study investigates the role of a low level of Stat3 in the C17.2 neural stem cells, which are popular stem cell candidates for transplantation research. The results reveal that C17.2 neural stem cells will undergo increased differentiation into neurons without generating glia after knockdown of Stat3 expression via an interfering RNA expression plasmid. As constitutively activated Stat3 is considered to be an oncogene, this study raises the possibility of stem cell transplantation with a low level of Stat3 to reduce the oncogenesis and facilitate the generation of neurons.