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    Research Grants Awarded

    Targeting AlphaVBeta3 Integrin and Src to Alleviate Breast Cancer Progression Stimulated by TGF-beta

    Study Section:
    Tumor Cell Biology II

    Scientific Abstract:
    BACKGROUND. Mammary tumorigenesis converts TGFb from tumor suppressor to a promoter of breast cancer (BC) cell epithelial-mesenchymal transition (EMT), invasion, and metastasis. We recently established the essential function of alphaVbeta3 integrin and Src in facilitating EMT in mammary epithelial cells (MECs) stimulated with TGFb. Equally important, we demonstrated that introducing inactive beta3 integrins in highly malignant human BC cells reestablishes cytostasis mediated by TGFb and prevents its induction of invasion. HYPOTHESIS. Based on these findings, we hypothesize that inactivating alphaVbeta3 integrin and Src prevents the conversion of TGFb from a suppressor to a promoter of BC growth and invasion, thereby alleviating BC development and progression stimulated by TGFb. SPECIFIC AIMS. (1) To determine the molecular mechanisms that mediate beta3 integrin:TGFb receptor type II (TbR-II) complex formation; (2) to identify the Tyr residues in TbR-II and TbR-I that are phosphorylated by Src; and (3) to determine the effectiveness of interdicting alphaVbeta3 integrin and Src function to antagonize TGFb oncogenicity and BC progression in vivo. STUDY DESIGN. Structure-function analyses will be performed to determine whether the beta3 integrin:TbR-II interaction is direct or mediated by FAK, and to identify the minimal determinants operant in mediating the formation of these complexes. Biochemical analyses will be used to identify the Tyr residue(s) in TbR-I and TbR-II that are phosphorylated by Src. Cell biological assays will be performed to determine the impact of (i) disrupting beta3 integrin:TbR-II complex formation and (ii) expressing TbR-I and TbR-II mutants that lack Src phosphorylation sites on the response of normal and malignant MECs to TGFb. Genetic engineering will be used to interdict alphaVbeta3 integrin and Src function in highly malignant, metastatic MECs in an attempt to restore the tumor suppressing of TGFb in mammary tumors developed in nude mice. Finally, microarray analyses will be performed on the resulting primary tumors and metastases to define the metastatic gene signature induced by TGFb in metastatic breast cancers. POTENTIAL OUTCOMES AND BENEFITS OF THE RESEARCH. Deciphering the TGFb paradox ? i.e., the ability of breast cancer cells to convert TGFb from a tumor suppressor to a tumor promoter ? is key to understanding both the biology and pathology of TGFb during breast cancer development. This proposal will establish the molecular mechanisms whereby alphaVbeta3 and Src dictate neoplastic MEC responses to TGFb, and in doing so, will define the metastatic gene signature induced by TGFb. Our study also may lead to the development of novel MEC integrin- and Src-based diagnostics and, consequently, to the development of novel pharmacological interventions to antagonize the alphaVbeta3 integrin:Src:TGFb signaling axis, thus improving the prognosis and treatment of patients with metastatic breast cancer.

    Lay Abstract:
    Transforming growth factor-beta (TGF-beta) is a protein that inhibits cancer formation by preventing uncontrolled cell growth, a phenomenon exemplified in breast cancer. TGF-beta prevents mammary cell growth during all stages of breast development. Unfortunately, mutations and alterations in the TGF-beta system occur in breast cancer, thus converting TGF-beta from a brake to an accelerator of mammary tumorigenesis. These mutations also permit TGF-beta to stimulate breast cancer metastasis, which is the leading cause of breast cancer-related death. How TGF-beta suppresses this process in normal mammary cells, and conversely, promotes this process in cancerous mammary cells remains unknown. The ability of breast cancer cells to convert TGF-beta from a tumor suppressor to a tumor promoter is known as the "TGF-beta paradox." Solving this paradox ultimately may hold the key to unlocking the door to new pharmacological interventions designed to alleviate breast cancer. Integrins are proteins that facilitate communication between cells and their surroundings; they also regulate cell growth and motility. Unlike normal cells, breast cancer cells receive inappropriate messages from aberrantly expressed integrins, thereby promoting breast cancer cell growth and metastasis. We find that some integrins enhance the braking function of TGF-beta on cell growth, while others and their companion protein, Src, convert TGF-beta to an accelerator of cell growth. This proposal will analyze whether aberrant expression of one integrin, alphaVbeta3, together with its enhanced activation of Src, cooperate in switching TGF-beta from a suppressor to a promoter of breast cancer progression. We will manipulate alphaVbeta3 integrin and Src activity in breast cancers to prevent their development and metastasis stimulated by TGF-beta, as well as to determine how alphaVbeta3 integrin and Src impact TGF-beta. We also will analyze and compare the changes in gene expression that occur in metastatic breast cancers before and after manipulating their alphaVbeta3 integrin and Src activities. Our study will provide new insights into solving the TGF-beta paradox, and will define for the first time the ?genetic fingerprint? whereby TGF-beta promotes metastatic disease in patients with breast cancer. This knowledge can be applied to the design of novel pharmacological agents aimed at abrogating the tumor promoting effects of TGF-beta on breast cancer, as well as novel integrin- and Src-based diagnostics to aid in prognosticating and treating patients with metastatic breast cancer.