Cell Culture Model for Understanding Estrogen Receptor Regulation in Normal and Malignant Cells. Addendum.

摘要

One of the major obstacles to study the contribution of estrogen receptor (ER) to the initiation and progression of breast cancer is the lack of an appropriate culture model that duplicates the estrogenic effects seen in the normal gland in vivo. We postulate that the correct expression and function of ER depends on an appropriate microenvironment that preserves cell-cell and cell- matrix interactions. Here we determined that the extracellular matrix (ECM) modulates the expression and function of the ER. The stimulation of the ER- mediated response by the presence of cell-matrix interactions involves the a6 integrin subunit. Using quantitative RT-PCR and western blots we also demonstrated that both normal and tumorigenic mouse mammary cell lines in culture increased ERa expression levels in response to ECM and that those levels are higher in the tumorigenic cell line. Moreover, the presence of estradiol decreased the expression of its own receptor in both cell types, two-fold in normal cells and fifteen-fold in tumorigenic cells. Therefore, we believe that the regulatory effect of ECM is exerted, at least in part, by modulating both the ER-mediated response and/or ERa levels itself. In addition, we have developed an in vitr0 culture system for mouse mammary cells isolated from the gland, which partly prevents the loss of ERa expression normally seen in standard culture conditions. This improved technique relies on culturing the cells in 3D cultures inside collagen I gels or on top of Matrigel instead of 2D monolayers, and the addition of lactogenic hormones. These results suggest that the approach that we have chosen to analyze the regulation of ER function by a three-dimensional matrix is promising. The regulation of ER by ECM could be a crucial step in the progression of breast cancer from an ER-positive to an ER- negative tumor, which leads to a hormone-independent and more aggressive cancer phenotype. In addition, manipulating ER expression in mammary cells b7.