Persistent activation of Stat3 signaling induces survivin gene expression and confers resistance to apoptosis in human breast cancer cells
ABSTRACT Signal transducer and activator of transcription 3 (Stat3) protein is persistently activated in breast cancer and promotes tumor cell survival. To gain a better understanding of the role of constitutive Stat3 signaling in breast cancer progression, we evaluated the expression profile of potential Stat3-regulated genes that may confer resistance to apoptosis.
Stat3 signaling was blocked with antisense oligonucleotides in human MDA-MB-435s breast cancer cells and Affymetrix GeneChip microarray analysis was done. The candidate Stat3 target gene Survivin was further evaluated in molecular assays using cultured breast cancer cells and immunohistochemistry of breast tumor specimens.
Survivin, a member of the inhibitor of apoptosis protein family, was identified as a potential Stat3-regulated gene by microarray analysis. This was confirmed in Survivin gene promoter studies and chromatin immunoprecipitation assays showing that Stat3 directly binds to and regulates the Survivin promoter. Furthermore, direct inhibition of Stat3 signaling blocked the expression of Survivin protein and induced apoptosis in breast cancer cells. Direct inhibition of Survivin expression also induced apoptosis. Increased Survivin protein expression correlates significantly (P = 0.001) with elevated Stat3 activity in primary breast tumor specimens from high-risk patients who were resistant to chemotherapy treatment.
We identify Survivin as a direct downstream target gene of Stat3 in human breast cancer cells that is critical for their survival in culture. Our findings suggest that activated Stat3 signaling contributes to breast cancer progression and resistance to chemotherapy by, at least in part, inducing expression of the antiapoptotic protein, Survivin.
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ABSTRACT: STAT3 upregulates expression of HIF-1 induced EPO. Receptor EPOR was reported to activate STAT3. Our study was aimed at demonstration of tissue immunoreactivities of those proteins and determination of their relationships in reference to clinicopathological variables of breast cancers. We detected STAT3, HIF-1alpha, EPO and EPOR in specimens of 76 human, female, ductal breast cancers by immunohistochemistry. STAT3 was detected in 38 of 76 cancers (50%). HIF-1alpha was found in 55 cases (72%). EPO positive tumors comprised 89% of all the cancers (68 cases). EPOR was also visualized in 55 cases (72%). Anti-HIF-1alpha and anti-STAT3 stained nuclei and cytoplasm of breast cancer cells in diffuse and finely granular fashion. Strong membranous expressions of EPO and EPOR were distributed in cytoplasmic and membranous granularity or diffuse staining. STAT3 correlated with HIF-1 in general (r=0.4012, p<0.0001) and in different patients' subgroups. STAT3 was significantly associated with EPO and EPOR in all the cancers (r=0.2370, p=0.039 and r=0.3336, p=0.003, respectively). Besides a correlation between STAT3 and EPOR in node negative ones, STAT3 wasn't related to EPO and EPOR in remaining subgroups. HIF-1alpha correlated with EPO and EPOR in most of analyzed groups. Immunoreactivity to EPO generally was associated with EPOR (r=0.3520, p=0.002). Statistically analyzed distributions of the proteins reflected functional dependences among STAT3, HIF-1alpha, EPO and EPOR in cellular signal conduction.Folia Histochemica et Cytobiologica 01/2007; 45(2):81-6. · 1.00 Impact Factor
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ABSTRACT: Signal transducer and activator of transcription 3 (STAT3) plays an important role in the tumor formation and metastasis. In this study, short hairpin RNA targeting STAT3 was cloned into pGenesil-2 plasmid vector and the effects of STAT3 silencing in 4T1 breast cancer cells were analyzed both in vitro and in vivo. Forty-eight hours after transfecting with pSi-STAT3, the expression level of STAT3, the upstream regulator and downstream targets were measured using Western blot. Moreover, the effects of pSi-STAT3 on migration and invasion in 4T1 cells were tested using wound-healing and tube formation assay. Furthermore, 4T1 subcutaneous mice model was used to evaluate the effects of pSi-STAT3 on tumor growth and metastasis. Proliferation, apoptosis, angiogenesis in tumor tissues and lung metastases were measured by PCNA, TUNEL, and CD31 immunostaining, respectively. Our results indicated that siRNA targeting STAT3 could significantly silence STAT3 expression in 4T1 breast cancer cells and result in inhibition of 4T1 breast cells migration and HUVECs tube formation. In vivo, pSi-STAT3 delayed tumor growth (pknockdown of STAT3 by plasmid-based siRNA might be a potential therapy against breast cancer.Neoplasma 01/2011; 58(6):538-47. DOI:10.4149/neo_2011_06_538 · 1.64 Impact Factor
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ABSTRACT: Tellurium is a rare element, which has been regarded as a toxic, non-essential trace element; its biological role, if any, has not been clearly established to date. The investigation of therapeutic activities of tellurium compounds is rather limited in the literature, despite the relative abundance of tellurium in the human body. Nevertheless, the varied activities of tellurium agents in both malignant and normal cells are extremely exciting, though very complex. Not surprisingly, an increased interest in tellurium among biological chemists and pharmacists has fuelled the search for more and more diverse tellurium compounds. The present review will focus on two small inorganic tellurium complexes, ammonium trichloro(dioxoethylene-O,O')tellurate (AS101) and Octa-O-bis-(R,R)-tartarate ditellurane (SAS), thoroughly investigated by us, converging at their anti-cancer properties, and elucidating their mechanism of action. AS101 is probably the most extensively studied synthetic tellurium compound from the standpoint of its biological activity. It is a potent immunomodulator (both in vitro and in vivo) with a variety of potential therapeutic applications. It is probably the only tellurium compound to be tested in phase I/II clinical studies in cancer patients. The effects of AS101 and SAS are primarily caused by their specific Te(IV) redox-modulating activities enabling the inactivation of cysteine proteases such as cathepsin B, inhibition of specific tumor survival proteins like survivin, or obstruction of tumor IL-10 production. All of these have profound consequences regarding anti-tumor activity or sensitization of tumors to chemotherapy. These properties, coupled with the excellent safety profile of the compounds, suggest promising anti-cancer therapeutic potential for tellurium compounds such as AS101 or SAS.Seminars in Cancer Biology 12/2011; 22(1):60-9. DOI:10.1016/j.semcancer.2011.12.003 · 9.14 Impact Factor