IKKβ Mediates Cell Shape-Induced Aromatase Expression and Estrogen Biosynthesis in Adipose Stromal Cells

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Abstract
Aromatase (Cyp19) is a key enzyme in estrogen biosynthesis and an important target in breast cancer therapy. Within tumor microenvironment, tumor cells stimulate aromatase expression in adipose stromal cells (ASCs), which in turn promotes estrogen-dependent growth of estrogen receptor (ER)-positive tumor cells. However, it is not clear how aromatase transcription and estrogen biosynthesis are regulated in ASCs under a precancerous condition. Here we demonstrate that cell shape change alone is sufficient to induce aromatase expression in primary ASCs from cancer-free individuals. The activation of aromatase transcription is mediated by IκB kinase-β (IKKβ), a kinase previously known for its cancer-promoting activity in tumor cells. Activation of IKKβ leads to elevated expression of transcription factor CCAAT/enhancer-binding protein-β (C/EBPβ), which binds to and stimulates two breast cancer-associated promoters of the aromatase gene. We also show that shape-induced estrogen production in ASCs can stimulate estrogen-dependent transcription in ER-positive breast tumor cells. We suggest that IKKβ-dependent aromatase induction due to changes in cellular architecture in adipose tissue may contribute to the breast cancer risks associated with high mammagraphic density and obesity.