Susan G Komen  
I've Been Diagnosed With Breast Cancer Someone I Know Was Diagnosed Share Your Story Join Us And Stay Informed Donate To End Breast Cancer
    Home > Research & Grants > Grants Program > Research Grants > Research Grants Awarded > Abstract

    Research Grants Awarded

    Elucidating The Tumor Suppressor Function Of Tbetariii In Breast Carcinogenesis

    Grant Mechanism:
    Postdoctoral Fellowships

    Scientific Abstract:
    Scientific Rationale: Transforming growth factor beta (TGF-beta) is a cytokine which regulates cell proliferation, differentiation, and apoptosis in a cell type and context specific manner. TGF-beta signaling is regulated by a co-receptor, the type III TGF-beta receptor (TbetaRIII), which mediates ligand binding and signaling through the type I and type II TGF-beta receptors. In addition, soluble TbetaRIII (sTbetaRIII), which is generated through ectodomain shedding of the TbetaRIII receptor, can inhibit TGF-beta signaling by sequestering ligand, resulting in the down-regulation of TGF-beta mediated signaling. Transgenic mice over-expressing TGF-beta exhibit altered mammary gland development, characterized by reduced ductal outgrowth and branching in virgin glands. In addition to its role in mammary gland development, the TGF-beta signaling pathway also has a dichotomous function in breast cancer development. In early stage breast tumors TGF-beta functions as a tumor suppressor, while in late-stage tumors TGF-beta signaling has a tumor promoting effect. Consistent with these observations, we have recently shown that the loss of TbetaRIII expression is a frequent early event in human breast cancers. Furthermore, restoring TbetaRIII expression in murine model of mammary cancer was shown to inhibit tumor invasion, angiogenesis, and metastasis, supporting TbetaRIII as a tumor suppressor in breast cancer. The tumor suppressor function of TbetaRIII appears to be due, in part, to the generation of sTbetaRIII, which antagonizes the tumor promoting effects of TGF-beta signaling in late stage mammary tumors. However, this suggests that increasing TbetaRIII expression prior to the initiation of mammary carcinogenesis may promote tumorigenesis due to the increased expression of sTbetaRIII and subsequent down-regulation of TGF-beta signaling. We have recently generated MMTV-TbetaRIII mice which over-express TbetaRIII in the mammary gland to determine the effect of TbetaRIII on mammary gland development and breast cancer initiation and progression in vivo. Hypothesis: We hypothesize that increased TbetaRIII expression will increase production of sTbetaRIII, thereby inhibiting TGF-beta signaling, leading to accelerated mammary gland development as well as the promotion of early-stage mammary carcinogenesis. However, during later-stage mammary tumors, TbetaRIII, through sTbetaRIII production, will inhibit tumor progression by limiting tumor invasion and migration. Specific Aims and Study Design: Aim 1: Establish whether MMTV-TbetaRIII mice exhibit accelerated mammary gland development. In this aim, mammary gland morphology will be examined by whole mount analysis of 8 week virgin, mid-pregnant, lactating, and involuting mammary glands. Levels of proliferation and apoptosis will be assessed during development in wild type and MMTV-TbetaRIII mammary glands. Aim 2: Establish whether MMTV-TbetaRIII mice exhibit elevated circulating levels of sTbetaRIII and decreased TGF-beta signaling and responsiveness. In this aim, Smad-dependent (Smad2/3) and Smad-independent (ERK, p38, JNK) signaling will be characterized in MMTV-TbetaRIII mammary glands. Levels of sTbetaRIII will be examined in wild-type and MMTV-TbetaRIII mice. Mammary epithelial cell (MEC) lines from wild type and MMTV-TbetaRIII mammary glands will be created to examine TGF-beta signaling, proliferation, and apoptosis in the absence and presence of TGF-beta. Aim 3: Establish whether increased TbetaRIII expression promotes mammary cancer initiation, but inhibits cancer progression in MMTV-TbetaRIII mice. MMTV-TbetaRIII and wild type mice will be treated with the chemical carcinogen DMBA and monitored for tumor latency, incidence, and metastasis over their lifespan. Proliferation, apoptosis, invasiveness, angiogenesis, and TbetaRIII expression will be examined in mammary tumors that develop. In addition, MMTV-TbetaRIII mice will be crossed to MMTV-her2/neu mice, which undergo spontaneous mammary tumorigenesis, and monitored as above over their lifespan. Mammary tumors that develop will be analyzed as above. Specific Aim 4: Establish whether TbetaRIII exerts its inhibitory effects on tumor progression through inhibition of directed migration and invasion. In this aim, motility, invasion, and wound healing assays will be performed with MMTV-TbetaRIII MEC lines and in TbetaRIII expressing and non-expressing tumor derived cell lines in the presence and absence of TGF-beta. Additionally, the actin cytoskeleton, focal complex formation, and polarity of epithelial cells will be examined in wildtype and MMTV-TbetaRIII MEC lines. Advancement of Field: This study aims to determine the role of TbetaRIII in mammary gland development and to further characterize its role as a tumor suppressor. Establishing the role of TbetaRIII and sTbetaRIII in normal mammary gland development will contribute to the understanding of their tumor suppressor function, as many developmental pathways are disregulated during tumorigenesis. These studies will determine if TbetaRIII over-expression, through the increased production of sTbetaRIII, will lead to a down regulation of TGF-beta signaling and the initiation of breast cancer, yet inhibit tumor progression through the inhibition of migration and invasion. These studies will define the effects of TbetaRIII over-expression on breast cancer initiation and progression and aid in targeting TbetaRIII and sTbetaRIII for the treatment of human breast cancers.

    Lay Abstract:
    Transforming growth factor beta (TGF-beta) regulates cell growth, cell survival, migration, and cell death in a cell type and context specific manner. TGF-beta signaling is regulated by a co-receptor, the type III TGF-beta receptor (TbetaRIII), which binds to TGF-beta and presents it to the type I and type II receptors. This activates the receptors and leads to the regulation of a number of genes involved in many cellular functions including cell growth, cell survival, and cell death. TbetaRIII can also down-regulate TGF-beta signaling through the production of soluble TbetaRIII (sTbetaRIII), a circulating, non-membrane bound version of the receptor. sTbetaRIII binds to TGF-beta, which prevents TGF-beta from binding and activating its receptors, leading to a decrease in TGF-beta signaling. Many human cancers exhibit alterations in the TGF-beta signaling pathway including mutations or deletions of pathway components or resistance to TGF-beta mediated inhibition of cell growth. Mice which have been engineered to over-express TGF-beta in the mammary gland exhibit inhibition of mammary gland development. In addition to its role in mammary gland development, the TGF-beta signaling pathway also has a dual role in breast cancer development. In early stage breast tumors TGF-beta has a tumor suppressing effect, while in late-stage tumors TGF-beta signaling has a tumor promoting effect. We have recently shown that the loss of TbetaRIII expression occurs early in the development of human breast cancer. Furthermore, restoring TbetaRIII expression in mouse mammary cancer cells was shown to inhibit tumor metastasis in a mouse model, supporting TbetaRIII as a tumor suppressor in breast cancer. The ability of TbetaRIII to function as a tumor suppressor appears to be due, in part, to the generation of sTbetaRIII, which inhibits the tumor promoting effects of TGF-beta signaling in late stage mammary tumors. However, increasing TbetaRIII expression prior to the initiation of mammary cancer may promote tumorigenesis due to the increase in levels of sTbetaRIII and subsequent down-regulation of TGF-beta signaling. We have recently generated mice which over-express TbetaRIII in the mammary gland. We hypothesize that increased TbetaRIII expression will lead to the increased production of sTbetaRIII, causing the down-regulation of TGF-beta signaling and resulting in accelerated mammary gland development as well as the promotion of early-stage mammary carcinogenesis. However, during late-stage mammary tumors TbetaRIII, through the production of sTbetaRIII and subsequent decrease in TGF-B signaling, will inhibit tumor progression and metastasis by limiting tumor invasion and migration. The goals of this proposal are to determine how TbetaRIII contributes to normal mammary gland development and to determine its effects on the initiation and progression of mammary tumors. Mice which over-express TbetaRIII in the mammary gland will be examined for defects in mammary gland development, including alterations in cell growth and cell death during development. The TbetaRIII over-expressing mammary glands will be examined for any changes in TGF-beta signaling and levels of sTbetaRIII will be examined in the TbetaRIII over-expressing mice. To determine the role of TbetaRIII in mammary tumor formation, wild type and TbetaRIII over-expressing mice will be treated with a chemical that can induce tumors, DMBA, and also interbred with mice that have been engineered to develop mammary cancers by over-expressing her2/neu in the mammary gland. These mice will then be monitored for the formation of tumors and any metastasis that develop. Any tumors that develop in the wild type, TbetaRIII, her2/neu, or TbetaRIII-her2/neu mice will be examined for physical and genetic changes, including cell growth, cell death, blood vessel formation, and metastasis. To determine whether TbetaRIII exerts it tumor suppressor effects through the inhibition of metastasis, cell migration and invasion will be examined in cell lines created from wild type mouse mammary glands and mammary glands over-expressing TbetaRIII. This study aims to determine the role of TbetaRIII in mammary gland development and to further characterize its role and mechanism as a tumor suppressor by using a mouse model of TbetaRIII over-expression. Determining the role of TbetaRIII and sTbetaRIII in normal mammary gland development will contribute to the understanding of their tumor suppressor function, as many signaling pathways that play a role in development are misregulated during tumorigenesis. These studies will determine if TbetaRIII over-expression, through the increased production of sTbetaRIII, will lead to a down regulation of TGF-beta signaling and the initiation of breast cancer, yet inhibit tumor progression through the inhibition of migration and invasion, two processes important for metastasis. These studies will determine the effects of TbetaRIII over-expression on breast cancer initiation and progression, identify TbetaRIII and sTbetaRIII as potential targets for human therapeutic treatments, and aid in the targeting of TbetaRIII, sTbetaRIII, and the TGF-beta signaling pathway for the treatment of various stages of human breast cancers.