A laminin-rich basement membrane matrix influences estrogen receptor B expression and morphology of MDA-MB-231 breast cancer cells

The expression of the estrogen receptor beta (ER beta) has been shown to play an important role in breast cancer. There is emerging hope that ER beta and its isoforms will be used as prognostic markers or as therapeutic targets in the clinical management of breast cancer. Many studies indicate that ER beta is down regulated during carcinogenesis. However, it is still unknown which signals can regulate ER beta expression. Basement membrane (BM) components have been shown to influence the expression levels of ER alpha and progesterone receptor. Therefore, we hypothesized that cell-matrix interactions can also affect the expression of ER beta and its isoforms. To test this we performed Matrigel assays using an ER alpha negative breast cancer cell line. MDA-MB-231 cells were plated on Matrigel, a reconstituted laminin-rich BM matrix, or on uncoated plastic culture plates. To investigate the effects of specific BM components we also cultured the cells on gels of purified collagen type IV and laminin-111. ER beta expression levels were investigated after 24, 48 and 72 h by RT-PCRs which allow to distinguish between different ER beta isoforms. MDA-MB-231 cells cultured on tissue culture plastic showed increased levels of ER beta 1 mRNA after 48 h. However, in cells cultured on Matrigel signals for ER beta 1 expression stayed at very low, nearly undetectable levels. Laminin-111 was identified to be the protein that represses ER beta 1 expression at the mRNA stage. Collagen type IV showed no effect on ER beta expression. We further observed that MDA-MB-231 cells on Matrigel organize into cell aggregates which are connected in web-like structures that appear similar to lactiferous ducts. These data suggest that interactions of breast cancer cells with the BM protein laminin-111 suppress the expression of ER beta 1 at the mRNA level. A laminin-111-rich microenvironment seems to keep ER beta 1 at very low levels in breast cancer cells.