Browsing by Subject "extracellular matrix"

Extracellular matrix components such as laminins have important roles in supporting the mammary gland epithelium and guiding its development and homeostasis. Adhesion to laminin alpha-5 subunit (Lama5), notably secreted by the hormone receptor positive luminal epithelial cells, promotes luminal epithelial differentiation and cellular identity, as well as controls mammary progenitor activity, contributing to physiological growth of the mammary epithelium. Lama5 loss in luminal mammary epithelial cells results in abnormal epithelial differentiation, aberrated ductal development, and diminished mammary epithelial growth in mice. Breast cancer is one of the most common forms of cancer, and the most common subtypes are hormone receptor positive luminal breast cancers. While expression of other epithelial laminin alpha subunits is often lost, Lama5 is commonly overexpressed in human breast cancer cells, notably in luminal cancer subtypes, as opposed to basal-like and other cancers subtypes. However, the role of Lama5 in mammary tumor growth and identity has not been experimentally studied in neither mice nor humans. In this thesis, the role of Lama5 in the growth and identity of mammary tumors was studied using both in vivo mouse and in vitro human approaches. Lama5 deletion in luminal epithelial cells of tumor-bearing mice was shown to result in five-fold decrease in the amount of tumorous growth in mouse mammary glands in vivo. In vitro LAMA5 downregulation of MCF-7 luminal human breast cancer cells was shown to lower the proliferation rate and increase the doubling time in 2D culture, decrease their mammosphere forming capacity, as well as decrease total growth in 3D culture, while no effects were observed in triple-negative basal-like MDA-MB-231 human breast cancer cells with LAMA5 downregulation. Additionally, downregulation of LAMA5 was shown to promote the expression of basal-like breast cancer and EMT markers vimentin and fibronectin in luminal MCF-7 cells, while the expression of luminal identity markers was not altered. No changes in the expression of luminal or basal cytokeratin markers CK8 and CK14 were seen in mammary tumors in vivo on mice with luminal laminin alpha-5 deletion. This thesis provides the first set of experimental evidence of the role of laminin alpha-5 as a factor promoting mammary tumor growth in both mice and human cells, especially in hormone receptor positive luminal cancer types. Lama5 contribution to tumor identity, and the exact mechanisms require further studies.