Activation of JAK2/STAT3 signaling by osteopontin promotes tumor growth in human breast cancer cells

• Published in: Carcinogenesis (New York) Vol. 31; no. 2; pp. 192 - 200
• Main Authors: Behera, Reeti, Kumar, Vinit, Lohite, Kirti, Karnik, Swapnil, Kundu, Gopal C.
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01.02.2010
• Subjects: Animals; Apoptosis - drug effects; Biological and medical sciences; Blotting, Western; Breast Neoplasms - metabolism; Breast Neoplasms - pathology; Carcinogenesis, carcinogens and anticarcinogens; Cell Adhesion - drug effects; Cell Movement - drug effects; Cell Nucleus - drug effects; Cell Nucleus - metabolism; Cell Proliferation - drug effects; Electrophoretic Mobility Shift Assay; Female; Flow Cytometry; Fluorescent Antibody Technique; Gynecology. Andrology. Obstetrics; Humans; Immunoenzyme Techniques; Integrin alphaVbeta3 - metabolism; Janus Kinase 2 - metabolism; Mammary gland diseases; Medical sciences; Mice; Mice, Inbred NOD; Mice, SCID; Osteopontin - pharmacology; Phosphorylation; Protein Transport; Signal Transduction; STAT3 Transcription Factor - metabolism; Tumor Cells, Cultured; Tumors; Xenograft Model Antitumor Assays; Human; Breast disease; Enzyme; JAK2 protein tyrosine kinase; Transferases; Osteopontin; Activation; Breast cancer; Malignant tumor; Mammary gland diseases; Signal transduction; Tumor growth; Transcription factor STAT3; Protein-tyrosine kinase; Tumor cell; Cancer
• ISSN: 0143-3334; 1460-2180
• DOI: 10.1093/carcin/bgp289

Deregulation of signal transducer and activator of transcription (STAT)-3 signaling plays crucial role in oncogenesis of various cancers. However, the molecular mechanism by which osteopontin (OPN), a chemokine-like extracellular matrix-associated protein, regulates STAT3 activation that leads to tumor progression and inhibits apoptosis in breast cancer cells is not well understood. In this study, we for the first time report that OPN upregulates αvβ3 integrin-mediated Janus kinase 2 (JAK2) phosphorylation and STAT3 activation in breast cancer (MDA-MB-468 and MCF-7) cells. Pretreatment of cells with JAK2 inhibitor (AG 490) suppresses OPN-induced STAT3 phosphorylation, its nuclear localization and DNA binding indicating that JAK2 is involved in this process. Transfection of cells with wild-type (wt) STAT3 enhanced whereas mutant STAT3 (STAT3 Y705F) suppressed OPN-induced breast tumor cell migration. Treatment of cells with OPN followed by staurosporine (STS) showed that OPN protects the cells from STS-induced apoptosis. Moreover, transfection of cells with wt STAT3 upregulates whereas STAT3 Y705F downregulates Bcl2 and cyclin D1 expressions in response to OPN. Interestingly, STAT3-overexpressing cells when injected to non-obese diabetic/severe combined immunodeficiency mice followed by OPN treatment, the mice developed enhanced tumor growth as compared with STAT3 Y705F-injected mice or mice injected with OPN alone. The levels of Bcl2 and cyclin D1 in wt STAT3 tumors were significantly higher than controls. Clinical specimen analysis revealed that increased OPN and pSTAT3 expressions correlate with enhanced breast tumor progression. Thus, targeting OPN and its regulated STAT3 signaling could be a potent therapeutic approach and understanding these mechanisms may form the basis of new therapeutic regimen for the management of breast cancer.