PGE2 downregulates tumour suppressor p53 and enhances aromatase expression in human breast adipose stromal cells (#65)
Background: The majority of postmenopausal breast cancers are dependent on locally produced oestrogens for their proliferation. Oestrogens are converted from androgens by aromatase and aromatase expression in breast adipose stromal cells (ASCs) adjacent to a tumour is increased in response to tumour-derived factors such as PGE2 via the activation of its proximal promoter II. p53 is a tumour suppressor and women with breast cancer often carry sporadic mutations in the gene that encodes p53. However, mutations in p53 in ASCs are infrequent. We have identified three putative p53 response elements on PII. This study aimed to determine the role of p53 in regulating aromatase expression and the effect of PGE2 on p53 expression and activity in human ASCs in the context of postmenopausal breast cancer.
Methods: Primary ASCs, isolated from breast reduction surgery, were treated with PGE2 or FSK/PMA (PGE2 mimetic) and/or RITA/Nutlin-3 (to stabilise p53). Aromatase, p53 and 18s or beta-actin (housekeeping gene) transcript expression was examined by real-time PCR. Reporter assays were performed to determine the effect of different treatments on PII and p53 activities in HEK293 cells. Immunofluorescence was performed to determine effect of PGE2 on p53 subcellular localisation in ASCs and compare the expression of p53 in tumour-free and tumour-bearing-breast tissue.
Results: RITA-stabilised p53 significantly reduced the PGE2 or FSK/PMA-induced aromatase expression and PII activity. FSK/PMA treatment significantly decreased p53 expression and transcriptional activity. Immunofluorescence showed that FSK/PMA and PGE2 treatment decreased p53 nuclear expression in hASC and enhanced perinuclear p53 expression was found in tumour-bearing tissue. ChIP demonstrated that p53 interacts with PII under basal conditions and that this interaction is decreased with FSK/PMA. In conclusion, p53 is a negative regulator of aromatase and its inhibition by PGE2 provides a novel mechanism for aromatase regulation in breast cancer.