ABSTRACT
Estrogen effects on mammary epithelial and breast cancer (BC) cells are mediated by the nuclear receptors ERα and ERß, transcription factors that display functional antagonism with each other, with ERß acting as oncosuppressor and interfering with the effects of ERα on cell proliferation, tumor promotion and progression. Indeed, hormone-responsive, ERα+ BC cells often lack ERß, which when present associates with a less aggressive clinical phenotype of the disease. Recent evidences point to a significant role of microRNAs (miRNAs) in BC, where specific miRNA expression profiles associate with distinct clinical and biological phenotypes of the lesion. Considering the possibility that ERß might influence BC cell behavior via miRNAs, we compared miRNome expression in ERß+ vs ERß- hormone-responsive BC cells and found a widespread effect of this ER subtype on the expression pattern of these non-coding RNAs. More importantly, the expression pattern of 67 miRNAs, including 10 regulated by ERß in BC cells, clearly distinguishes ERß+, node-negative, from ERß-, metastatic, mammary tumors. Molecular dissection of miRNA biogenesis revealed multiple mechanisms for direct regulation of this process by ERß+ in BC cell nuclei. In particular, ERß downregulates miR-30a by binding to two specific sites proximal to the gene and thereby inhibiting pri-miR synthesis. On the other hand, the receptor promotes miR-23b, -27b and 24-1 accumulation in the cell by binding in close proximity of the corresponding gene cluster and preventing in situ the inhibitory effects of ERα on pri-miR maturation by the p68/DDX5-Drosha microprocessor complex. These results indicate that cell autonomous regulation of miRNA expression is part of the mechanism of action of ERß in BC cells and could contribute to establishment or maintenance of a less aggressive tumor phenotype mediated by this nuclear receptor.
Subject(s)
Breast Neoplasms/genetics , Breast Neoplasms/metabolism , Estrogen Receptor beta/metabolism , Estrogens/metabolism , Gene Expression Regulation, Neoplastic , MicroRNAs/genetics , Cell Line, Tumor , Chromatin/metabolism , Cluster Analysis , Estrogen Receptor alpha/metabolism , Estrogen Receptor beta/genetics , Female , Gene Expression Profiling , Humans , Ribonuclease III/metabolismABSTRACT
The neurotransmitter acetylcholine (Ach) controls both excitatory and inhibitory synaptic transmission in the striatum. Here, we investigated the involvement of the endocannabinoid system in Ach-mediated inhibition of striatal GABA transmission, and the potential role of transient receptor potential vanilloid 1 (TRPV1) channels in the control of Ach-endocannabinoid coupling. We found that inhibition of Ach degradation and direct pharmacological stimulation of muscarinic M1 receptors reduced striatal inhibitory postsynaptic currents (IPSCs) through the stimulation of 2-arachidonoylglicerol (2AG) synthesis and the activation of cannabinoid CB1 receptors. The effects of M1 receptor activation on IPSCs were occlusive with those of metabotropic glutamate receptor 5 stimulation, and were prevented in the presence of capsaicin, agonist of TRPV1 channels. Elevation of anandamide (AEA) tone with URB597, a blocker of fatty acid amide hydrolase, mimicked the effects of capsaicin, indicating that endogenous AEA acts as an endovanilloid substance in the control of M1-dependent 2AG-mediated synaptic effects in the striatum. Accordingly, both capsaicin and URB597 effects were absent in mice lacking TRPV1 channels. Pharmacological interventions targeting AEA metabolism and TRPV1 channels might be considered alternative therapeutic routes in disorders of striatal cholinergic or endocannabinoid neurotransmission.
