PPAR-gamma ligands and adipocytes regulate expression of the plasminogen activator system in breast cancer.

摘要

There is a known association between a high-fat diet, excess adiposity and breast cancer development. While the mechanism is not fully understood, the goal of this project was to evaluate the effects of dietary fatty acids and adipocytes on tumor cell motility, as it relates to the plasminogen activator system. The plasminogen activator (PA) system is an important regulator of tumor cell motility, and is composed of the urokinase plasminogen activator (uPA), the urokinase cell surface receptor (uPAR) and the plasminogen activator inhibitor-1 (PAI-1). While PAI-1 functions to inhibit uPA activity, elevated levels of PAI-1 are paradoxically related to poor patient prognosis in breast cancer. In addition to being increased in breast cancer, PAI-1 is also upregulated in obese individuals, potentially the result of adipocyte overexpression of PAI-1. Although the literature is conflicting, elevated PAI-1 and obesity may be linked through the ligand activated transcription factor, peroxisome proliferator-activated receptor-gamma (PPAR-gamma), the master regulator of adipogenesis. This project began by characterizing the PA system in a series of cell lines which have been developed as an in vitro model of breast cancer progression. A significant difference in uPA expression was noted between the normal MCF-10A cells and the malignant MCF-10CA1 cells. Using these cells we investigated the effect of various PPAR-gamma agonists, including ciglitazone, arachidonic acid, an omega-6 fatty acid, and docosahexanoic acid, an omega-3 fatty acid, on cell motility. Treatment with ciglitazone reduced both motility of MCF-10A and MCF-10CA1 cells and PAI-1 protein expression. Using a PPAR-gamma antagonist, we show that these effects are PPAR-gamma independent. In contrast, arachidonic acid treatment increased cell motility of MCF-10A cell in a PPAR-gamma dependent manner. To study the effect of adipocytes on epithelial motility we used primary human breast adipocytes, which express significantly more PAI-1 than their precursor cells. Conditioned media from these adipocytes greatly increased both MCF-10A and MCF-10CA1 cell migration. We provide evidence which suggests treatment with adipocyte conditioned media increases uPA activity on the cell surface and increases phosphatidylinositide-3 kinase activity. The work presented in this dissertation is novel and provides evidence of a possible mechanism linking obesity, diet, and breast cancer development and progression, through the PA system.