Abstract P6-02-02: Altered matrix homeostasis regulates estrogen biosynthesis in adipose tissue

Several estrogen-dependent pathological conditions including breast cancer, uterine fibroids, and endometriosis are associated with local overexpression of aromatase, a key enzyme in estrogen biosynthesis and important therapeutic target for postmenopausal ER+ breast cancer. In addition, excessive aromatase expression in adipose tissue at least partially accounts for obesity-associated breast cancer risk among postmenopausal women. While altered matrix homeostasis is associated with these aromatase-overexpressing tissues, little is known as to whether it can directly impact local steroidogenic gene expression and estrogen biosynthesis. A paucity of knowledge in this area is partly due to the lack of proper model systems that can recapitulate the mechanical properties of a cell9s microenvironment. Our data indicate that matrix alone can significantly stimulate aromatase transcription in breast stromal cells (BSCs) via distinct signaling pathways. With the help of a repertoire of molecular and biophysical tools, such as micropost, micropattern and polyacrylamide gel and 3-dimensional matrix culture, we determined that matrix rigidity and cellular shape play important role in the regulation of aromatase transcription in the BSCs. We further discovered that cytoskeleton dynamics can significantly alter the ECM-stimulated aromatase transcription in BSCs. Following careful and elaborate studies with the help of siRNA-mediated knockdown and over-expression of the individual factors, we found that a non-canonical collagen receptor member of discoidin domain receptor (DDR) family, DDR1, transduce the external signal inside the cells to facilitate the aromatase transcription. Further studies with siRNA-mediated knockdown and specific inhibitors revealed that DDR1 activates a signaling cascade, which promotes activation of the cJun kinase (JNK-1) by phosphorylation and subsequently the activation of Activation Protein-1 family member JunB. Activated JunB physically binds at the cancer-specific promoters of aromatase and induce transcription in stromal cells. To determine the consequence of the altered matrix generated aromatase on the growth of estrogen receptor (ER)-positive breast cancer cell lines we set up in vitro co-culture system. Proliferation of ZR75-1 and its ability to produce estrogen-stimulated genes were enhanced in multiple fold, when the cells were co-cultured physically with BSCs inside collagen or fed with BSC conditioned media in the presence of testosterone. The link between matrix homeostasis and hormone metabolism is a vastly under-explored topic. Results from our work has bridged a major gap of knowledge in this field. Findings from the study also identified new factors that are key for the tissue-specific activation of estrogen biosynthesis and provide novel prognostic tools and markers, as well as new therapeutic targets for reducing local estrogen production, thus overcoming the side effects often associated with systemic inhibition of aromatase. The proposed work promises to establish a novel paradigm for regulation of steroidogenic gene expression and estrogen production and may have a far-reaching impact on the etiology and treatment of endocrine diseases that are associated with altered matrix homeostasis. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-02-02.