Aromatase inhibitor treatment of breast cancer cells increases the expression of let‐7f, a microRNA targeting CYP19A1

Abstract

Aromatase inhibitors (AIs) are considered the gold standard of endocrine therapy for oestrogen receptor-positive postmenopausal breast cancer patients. AI treatment was reported to result in marked alterations of genetic profiles in cancer tissues but its detailed molecular mechanisms have not been elucidated. Therefore, we profiled miRNA expression before and after treatment with letrozole in MCF-7 co-cultured with primary breast cancer stromal cells. Letrozole significantly altered the expression profiles of cancer miRNAs in vitro. Among the elevated miRNAs following letrozole treatment, computational analysis identified let-7f, a tumour-suppressor miRNA which targeted the aromatase gene (CYP19A1) expression. Quantitative real-time PCR assay using MCF-7 and SK-BR-3 cells as well as clinical specimens of a neoadjuvant study demonstrated a significant inverse correlation between aromatase mRNA and let-7f expression. In addition, high let-7f expression was significantly correlated with low aromatase protein levels evaluated by both immunohistochemistry and the western blotting method in breast cancer cases. Results of 3'UTR luciferase assay also demonstrated the actual let-7f binding sites in CYP19A1, indicating that let-7f directly targets the aromatase gene. Subsequent WST-8 and migration assays performed in let-7f-transfected MCF-7 and SK-BR-3 cells revealed a significant decrement of their proliferation and migration. These findings all demonstrated that let-7f, a tumour suppressor miRNA in breast cancer, directly targeted the aromatase gene and was restored by AI treatment. Therefore, AIs may exert tumour-suppressing effects upon breast cancer cells by suppressing aromatase gene expression via restoration of let-7f.

Aromatase inhibitor regulates let-7 expression and let-7f–induced cell migration in endometrial cells from women with endometriosis

“…Treatment with the let-7f mimic resulted in an approximately 100-fold increase in let-7f expression compared with has-mir-negative control treatment (data not shown). Since let-7f has been shown to target the aromatase gene (4), we evaluated aromatase expression in Ishikawa cell lines and endometrial stromal cells from the patients with endometriosis after let-7f mimic transfection. After 48 hours of let-7f mimic treatment, aromatase mRNA expression was significantly decreased in both Ishikawa cell lines and endometrial stromal cells (0.36-fold increase, P =0.002 and 0.61-fold increase, P =0.025, respectively) (Figure 2A, B).…”

“…Recently, it has been shown that AI treatment of breast cancer cells increases the expression of let-7f , a microRNA targeting aromatase gene (CYP19A1)(4). MicroRNAs (miRNAs) are a family of endogenous, small (approximately 22 nucleotides in length), noncoding, functional RNAs which regulate gene expression either by translational repression or degradation of messenger RNA transcripts after targeting the 3′ UTR.…”

Recent trends in microRNA research into breast cancer with particular focus on the associations between microRNAs and intrinsic subtypes

“…miRNAs expression profiling before and after letrozole treatment reveal post-treatment increases in let-7f expression in both the preclinical and clinical settings. 62 miRNA and heat shock proteins in hormone receptor-positive/ HER2-negative breast cancer Heat shock protein (HSP) reveals various effects on multiple oncogenic signaling pathways. The function of HSP is generally considered to be ATP-dependent protein chaperoning.…”

Complexities of androgen receptor signalling in breast cancer

“…All enzymes are discussed in the text with the exception of oestrogen sulphotransferase (EST), which is an oestrogen-specific enzyme and hence outside the scope of this article, however, given its importance both biologically and therapeutically (reviewed by McNamara et al (2013b)) and as such is included in this diagram. Printed in Great Britain aromatase in ERa-positive MCF7 breast cancer cells (Shibahara et al 2012). Therefore, the protective actions of androgens, at least in ERa-positive breast cancers, may be partially achieved through down-regulation of aromatase and decreased intracrine synthesis of oestrogens.…”