Cell shape is a key determinant of estrogen biosynhesis in adipose stromal cells.

Abstract

Abstract Abstract #5061 BACKGROUND: Accumulating evidence suggests that obesity is a high risk factor for breast cancer among post-menopausal women, which can at least partially be explained by the contribution of adipose tissue to local and circulating estrogen. In response to tumor cell-secreted cytokines, adipose stromal cells (ASCs) express a large amount of aromatase, a key enzyme in estrogen biosynthesis and a clinically proven target for breast cancer therapy. Increased estrogen production from ASCs in turn stimulates hormone-dependent tumor growth, creating a “vicious cycle” between estrogen-dependent tumor cells and estrogen-producing ASCs that is conducive to mammary tumorigenesis. In contrast to our knowledge of aromatase expression in tumor-associated ASCs, relatively little is known about its regulation in ASCs under disease-free conditions. Could aromatase expression in ASCs be induced without the presence of tumor cells? Is there any genetic or epigenetic difference in the inducibility of aromatase expression in cancer-free individuals? If so, might the difference be related to breast cancer risk?
 Material and Methods: ASCs were isolated from cancer-free individuals by using blendzyme. ACSs were plated in confluent and subconfluent states for several days and then were harvested for RNA isolation, enzymatic activity and protein study. Specific genes were expressed in ASCs using lentiviral expression system and were depleted by siRNA method. Co-culture system was established using ASC and ZR-75 cell line. In a xenograft model, ASCs were injected with the ZR-75 cells in mammary fat pad.
 Results: Aromatase expression in ASCs can be stimulated up to several hundred folds by cell shape changes induced by various physical or chemical stimuli. Our work uncovered several key signal-transducing molecules including Inhibitory kB Kinases (IKKs) in mediating the cell shape-triggered aromatase expression. Unexpectedly, activation of aromatase gene expression following cell shape change does not involve activation of NFkB, a downstream effector of IKKs. Rather, aromatase induction following cell shape change positively correlated with the expression level of CEBPβ; and CEBPβ knockdown severely impaired aromatase expression. Significant increase in aromatase expression was due to activation of the same breast cancer-associated promoters that are robustly stimulated in intratumoral adipose tissue. In a coculture and invivo xenograft model, ACSs were able to trigger E2 responsive genes as well as stimulate early tumor occurence in ZR-75 cells, respectively.
 Discussion: Our study suggests that genetic and epigenetic alterations in aromatase-inducing signaling pathway may result in excessive estrogen production and thus breast cancer development. Excess aromatase produced by the stromal cells are capable of initiating tumor in surrounding breast epithelial cells. Study further uncovers a previously unappreciated paradigm for regulation of aromatase expression in adipose tissue, which should have a far-reaching impact on risk assessment and prevention of breast cancer. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 5061.