Quantitative analysis of aromatase mRNA expression derived from various promoters (I.4, I.3, PII and I.7) and its association with expression of TNF-alpha, IL-6 and COX-2 mRNAs in human breast cancer

Abstract

The purpose of the present study was to study the aromatase mRNA expression as well as promoter usage (I.4, I.3, PII and I.7) in axillary adipose tissue (AA), mammary adipose tissue (MA), breast tumor tissue (BT) and adjacent normal breast tissue (NB), and to study the relationship between aromatase mRNA expression and tumor necrosis factor (TNF)-alpha, interleukin (IL)-6 and cyclooxygenase (COX)-2 mRNA expression. BT (n=108), NB (n=54), AA (n=41) and MA (n=34) from patients with breast cancer were subjected to real-time PCR assays for the mRNA levels of aromatase, TNF-alpha, IL-6 and COX-2. We also studied the usage of promoters I.4, I.3, PII and the recently reported endothelial promoter I.7. Total aromatase mRNA levels were significantly up-regulated in BT as compared with NB, AA and MA. Proportion of promoter l.4-specific transcripts against the total transcripts was significantly decreased and that of promoter l.3- and l.7-specific transcripts was significantly increased in BT than NB, AA and MA. However, the amount of transcripts from all the 4 promoters was significantly up-regulated in BT than NB, AA and MA. Estrogen receptor-alpha (ER-alpha) positive tumors showed a higher percentage of promoter I.7 usage than ER-alpha negative tumors with a marginal significance (p=0.05), and tumor with high microvessel counts tended (p=0.06) to show a higher percentage of promoter I.7 usage than those with low microvessel counts. There was a significant association between aromatase mRNA levels and TNF-alpha, IL-6 or COX-2 mRNA levels in BT, AA and MA but not in NB. These results suggest that enhanced transcription of promoters l.4, I.3, PII and I.7 explains the up-regulation of aromatase mRNA levels in BT. It has also been suggested that angiogenesis might stimulate the growth of ER-alpha positive tumors through the enhanced transcription of aromatase from promoter I.7 in endothelial cells in BT, and that TNF-alpha, IL-6 and COX-2 might be implicated in the up-regulation of aromatase mRNA in BT, AA and MA but not in NB.