Andreia Bates, Ph.D.
Department: Cancer Biology, 2014
Faculty Mentor: Barbara Fingleton, Ph.D.
Dissertation Title: Roles of Fibroblast MMP2 in Breast to Lung Metastasis
Dissertation Abstract: Breast cancer five-year survival rates decrease from 99% for patients with local disease to 25% for those with distant metastases. The potential for tumor cells to proliferate in a foreign microenvironment and develop into overt metastases is mediated through interactions with stromal cells at the secondary site. Understanding the mechanisms underlying tumor cell cooperation with the stromal milieu to support the outgrowth of metastases is essential for increasing patient survival.
Matrix metalloproteinases (MMPs), including MMP2, are associated with metastatic progression. Preliminary studies found that loss of host MMP2 reduced the proliferation of experimental metastases in the lungs of mice, and identified fibroblasts in control tumor-bearing lungs as the major source of MMP2. In vitro, spheroidal mammary tumor growth was increased by co-culture with control fibroblasts isolated from tumor-bearing lungs but not when fibroblasts with Mmp2 knockdown were used. This result suggested that MMP2 was responsible for a tumor-proliferative, activated fibroblast phenotype.
The studies within this dissertation employ a combination of in vitro, in vivo, and correlation analyses using a human data set to investigate how MMP2 potentiates breast tumor outgrowth in the lungs. In vitro, exogenous active enzyme increased tumor cell proliferation in 3D but not 2D. Knockdown of Mmp2 in fibroblasts attenuated expression of two markers of activation (á-smooth muscle actin and vimentin). Additionally, Mmp2 knockdown fibroblasts showed significantly decreased expression of the matrix transcripts collagen I, collagen IV and fibronectin. Active TGFâ-1 was sufficient to rescue the MMP2-dependent collagen I and IV expression, while MMP2-induced collagen expression was blocked with addition of TGFâ-1 neutralizing antibody. Gene expression data in stromal cells of human breast cancers revealed that MMP2 expression is also positively correlated with activation and matrix transcripts. A model is presented whereby MMP2 production in tumor fibroblasts is important for the activity of TGFâ-1 cytokine and subsequent activation of fibroblasts to a matrix-producing, proliferation-supportive phenotype. Overall, these studies reveal a previously undefined role for MMP2 in metastatic outgrowth mediated by fibroblasts, and extends the mechanisms by which MMPs contribute to tumor progression.