Browsing by Subject "FGFR1"

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    FGFR1-induced soluble factors promote mammary tumorigenesis and chemoresistance
    (2013-08) Bade, Lindsey Kay
    The fibroblast growth factor receptor (FGFR) family consists of four receptor tyrosine kinases that are known regulators of cellular processes such as proliferation, migration, survival, and angiogenesis. Anomalous expression or uncontrolled activation of these receptors or their ligands has been correlated with progression of various types of cancer, including breast cancer. Specifically, the chromosomal locus of FGFR1, 8p11-12, is found to be aberrantly amplified in approximately 10% of patients diagnosed with breast cancer. Patients who harbor the FGFR1 amplification do not respond well to current therapies and develop resistance to hormone-based therapies. Therefore, understanding the molecular mechanisms of how FGFR1 overexpression promotes tumorigenesis may provide insights into better targets for novel, more effective therapies. The work presented here shows that FGFR1 activation significantly upregulates expression of the ligands AREG and EREG at the transcript and protein levels both in vitro and in vivo, which then activate EGFR signaling. AREG is critical for normal ductal morphogenesis in the mammary gland and has also been linked to breast cancer progression. Studies examining AREG expression in human breast cancers have found AREG expression to significantly correlate with regional lymph node metastases, large tumor size, and high-grade tumors. While EREG promotes proliferation of several normal and cancerous cell types, the role of EREG has not been extensively characterized in the mammary gland. However, recent studies have demonstrated that EREG is a potent mediator of metastasis of breast cancer cells to the lung and that overexpression of EREG is an indicator of poor prognosis for inflammatory breast cancer patients. EGFR, a member of the ErbB receptor tyrosine kinase family, has been well studied in the mammary gland, and it is known that EGFR is required for normal mammary gland ductal morphogenesis. Alternatively, overexpression or constitutive activation of EGFR in the mammary gland has been linked to mammary tumorigenesis. Additionally, overexpression of EGFR in the breast is associated with recurrence of earlier stage breast cancers and decreased disease-free and overall survival in later stage breast cancer patients. Notably, we demonstrate that EGFR activation is at least in part required for FGFR1-induced proliferation and migration and ERK1/2 activation, as inhibition of EGFR with the small molecule kinase inhibitor erlotinib significantly blocks these processes. Moreover, we show that FGFR1 and EGFR are co-expressed in TNBC cell lines and that both FGFR1 and EGFR can mediate Doxorubicin chemoresistance. We further show that FGFR1 upregulates expression of the cytokine LIF, which then signals through gp130/JAK to activate STAT3 in vitro. Directly inhibiting either FGFR1 or STAT3 significantly reduces chemoresistance and increases apoptosis in vitro. Furthermore, inhibition of FGFR1 with the small molecule inhibitor PD173074 results in increased chemosensitivity and apoptosis in a mouse model of mammary tumorigenesis. These results are significant because they are the first to show that FGFR1 signals through EGFR and that FGFR1 mediates chemoresistance through activation of STAT3. This study furthers our understanding of FGFR1-amplified mammary tumorigenesis and presents alternative factors for targeted therapies for patients with FGFR1-amplified breast cancers.
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    Fibroblast growth factor Receptor 1-induced osteopontin regulates proinflammatory molecules to mediate cross-talk between breast cancer cells and the surrounding tumor microenvironment
    (2012-06) Reed, Johanna Rae
    Tumor formation is an extensive process requiring complex interactions that involve both tumor cell-intrinsic pathways and soluble mediators within the microenvironment. Tumor cells exploit the intrinsic functions of many soluble molecules, including cytokines and chemokines and their receptors, to regulate pro-tumorigenic phenotypes that are required for development of the primary tumor. Previous studies demonstrated that activation of inducible FGFR1 (iFGFR1) in mammary epithelial cells resulted in increased proliferation, migration, and invasion in vitro and tumor formation in vivo. Early studies also indicated that iFGFR1 activation stimulated recruitment of macrophages to the epithelium resulting in increased epithelial cell proliferation and angiogenesis. Our current studies further examined this model to identify novel mechanisms that regulate early stage tumorigenesis with a specific emphasis on the soluble mediators that are regulated by iFGFR1 to promote epithelial and stromal cell migration. Results from this study elucidate a novel role for iFGFR1-induced osteopontin in promoting a proinflammatory tumor microenvironment through the regulation of proinflammatory molecules such as IL-1beta; and activation of the COX-2/PGE2 pathway as well as by promoting recruitment of CX3CR1-expressing macrophages through regulation of the chemokine CX3CL1. Defining the role of osteopontin-regulated proinflammatory, secreted molecules in promoting iFGFR1-mediated mammary tumorigenesis is important for understanding how initiating oncogenic events drive tumor growth and progression through the secretion of soluble mediators. Moreover, results from these studies will aid in identifying potential novel molecular targets for therapeutic intervention.