title: Involvement of early growth response factors in TNFα-induced aromatase expression in breast adipose.
abstract: Expression of the oestrogen producing enzyme, aromatase, is regulated in a tissue-specific manner by its encoding gene CYP19A1. In post-menopausal women, the major site for oestrogen production in the breast is the adipose, where CYP19A1 transcription is driven by the distal promoter I.4 (PI.4). Transcripts via this promoter are also elevated in breast adipose fibroblasts (BAFs) adjacent to a tumour. PI.4 expression is stimulated by a number of cytokines, and TNFα is one such factor. The transcriptional mechanisms induced by TNFα to stimulate PI.4 are poorly characterised. We show that the early growth response (Egr) transcription factors play an important role in the TNFα-induced signalling pathway resulting in elevated PI.4 transcription. TNFα treatment of BAFs increases mRNA levels of all four Egr family members, with EGR2 being the most highly expressed. Overexpression of EGR2 causes an increase in endogenous CYP19A1 expression in preadipocyte Simpson-Golabi-Behmel syndrome cells, driven by increases in PI.4-specific transcripts. PI.4 luciferase reporter activity is increased in a dose-dependent manner by EGR2, EGR3 and EGR4, with EGR2 showing the most potent activation of promoter activity. Deletion analysis indicates that this promoter activity is being indirectly mediated by a short region of the promoter not containing any previously characterised binding sites, and we further show that EGR2 does not bind directly or indirectly to this promoter region. However, siRNA knockdown of the Egrs reduces the total and PI.4-derived CYP19A1 transcription in BAFs. These studies unveil a novel component of the aromatase gene regulatory network and further enhance the complexity of oestrogen production in the breast.
authors: Cancer Drug Discovery Laboratory, Prince Henry's Institute of Medical Research, PO BOX 5152, Clayton, VIC 3168, Australia.
authors: Sarah Q
authors: SQ
authors: To
authors: Evan R
authors: ER
authors: Simpson
authors: Kevin C
authors: KC
authors: Knower
authors: Colin D
authors: CD
authors: Clyne
mesh_terms: D000273:Adipose Tissue / Q000187:drug effects* / Q000378:metabolism*; D000818:Animals; D001141:Aromatase / Q000235:genetics*; D001940:Breast / Q000166:cytology*; D002460:Cell Line; D051767:Early Growth Response Protein 2 / Q000235:genetics / Q000378:metabolism; D051765:Early Growth Response Transcription Factors / Q000235:genetics / Q000378:metabolism*; D005260:Female; D015870:Gene Expression; D005786:Gene Expression Regulation / Q000187:drug effects*; D017930:Genes, Reporter; D006801:Humans; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics; D020218:Response Elements; D017384:Sequence Deletion; D015533:Transcriptional Activation; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D051767:Early Growth Response Protein 2; D051765:Early Growth Response Transcription Factors; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D001141:Aromatase; C561410:CYP19A1 protein, human