Role of TGF-β signaling in carcinoma cell migration and tumor progression

Abstract

Transforming growth factor-beta (TGF-β) has a dual role during tumor progression initially as a suppressor and then as a promoter. Much is known about the contribution of TGF-β signaling to tumorigenesis, yet, the role of TGF-β in epithelial-stromal migration during tumor progression is poorly understood. In this dissertation, we hypothesized that TGF-β is a critical regulator of tumor-stromal interactions that promote mammary tumor cell migration and metastasis. Fluorescently-labeled murine mammary carcinoma cells, isolated from either MMTV-PyVmT TGF-β receptor II knockout (TβRII KO) or TβRIIfl/fl control mice, were combined with mammary fibroblasts and xenografted onto the chicken embryo chorioallantoic membrane. Intravital microscopy of xenografts revealed that fibroblast-stimulated carcinoma cells utilize TGF-β signaling to drive single cell/strand migration but migrate collectively in the absence of TGF-β signaling. At epithelial-stromal boundaries, single cell/strand migration of TβRIIfl/fl carcinoma cells was characterized by α-SMA and vimentin expression, while collective migration of TβRII KO carcinoma cells was identified by E-cadherin+/p120+/β-catenin+ clusters. TβRII KO tumors exhibited a two-fold greater metastasis than TβRIIfl/fl tumors, attributed to enhanced extravasation ability. In TβRII KO tumor epithelium compared to TβRIIfl/fl epithelium, Igfbp4 and Tspan13 expression was upregulated while Col1α2, Bmp7, Gng11, Vcan, Tmeff1, and Dsc2 expression was downregulated. Downregulation of Tmeff1 was correlated with disease progression of TGF-β-insensitive mammary cancer. Our findings concerning TGF-β signaling in stromal-epithelial interactions are important in identifying migratory mechanisms that can be targeted as recourse for breast cancer treatment. In the second part of this dissertation, the timing of TGF-β signaling in relation to tumor progression was investigated through the creation of an inducible dominant-negative TβRII (dnTβRII) mouse model (MMTV-PyVmT;MMTV-rtta;dnTβRII). We hypothesized that attenuation of TGF-β signaling prior to tumorigenesis leads to increased metastasis. Results indicated that animals with attenuated TGF-β signaling prior to tumor palpation exhibited increased tumor latency and enhanced metastasis of dnTβRII-expressing carcinoma cells. These animals had an increased MDSC tumor population, as well as increased carcinoma cell secretion of MCP-1/CCL2. Our inducible dnTβRII model has therapeutic implications in determining the necessary timing of therapeutic inhibition of TGF-β signaling during cancer progression.