TNFα induced aromatase expression is mediated by the Early Growth Response transcription factors in breast adipose
S. To1,2, E. Simpson1,2, K. Knower1 & C. Clyne1,2
Breast cancer remains the leading cause of cancer-related death in Australian women. Up to 70% of post-menopausal tumours are estrogen-receptor positive (ER+), dependent on estrogen for continued growth and proliferative advantage. Adjuvant anti-estrogen therapies are considered the cornerstone approach to the treatment of such tumours, and research is ongoing to maximize its effectiveness. The major source of estrogens for ER+ breast cancers is local conversion of androgen precursors by the enzyme P450 aromatase. Inflammatory factors such as Tumour Necrosis Factor-α (TNFα) stimulate transcription of CYP19A1, the gene that encodes aromatase, via its adipose-specific promoter I.4 (PI.4). The pathways by which this is achieved are not fully understood. We aim to identify the mechanisms underlying TNFα-dependent aromatase induction in the context of ER+ breast cancer.
TNFα treatment of human breast adipose fibroblasts (BAFs) increased mRNA levels of all four early growth response transcription factors, with a 7-fold EGR2 induction being the highest. Overexpression of EGR2 caused an increase in endogenous CYP19A1 expression in the human pre-adipocyte cell line SGBS, driven by increased PI.4-specific transcripts. PI.4 luciferase reporter activity is dose-dependently increased by EGR2, EGR3 and EGR4, with EGR2 causing a 70-fold luciferase response. Deletion analysis indicates this promoter activity was indirectly mediated by a short region of the promoter not containing any previously characterised binding sites, and we further show that EGR2 cannot bind directly to this promoter region. This suggests involvement of a secondary factor.
Our studies demonstrate that the Early Growth Response (Egr) transcription factors play an important role in the TNFα-induced signalling pathway resulting in elevated PI.4 transcription. This unveils a novel component of the aromatase gene regulatory network, and further enhances our understanding of estrogen production in the breast.
Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This work was supported, however funding details unavailable.