MicroRNAs are small non-coding RNA molecules that play a key role in gene regulation. The expression of miRNAs is associated with tumor growth, invasion, angiogenesis and metastasis of various types of cancer, such as breast cancer. During the tumor development, angiogenesis, the formation of new blood vessels, displays a vital role, allowing tumor progression and metastasis. Therefore, the search for inhibitors of this process has been a therapeutic strategy for cancer. Melatonin, a hormone produced and secreted by the pineal gland, is a possible treatment for breast cancer due to their oncostatic properties. Studies suggests that this hormone is able to modify the expression of numerous genes related to breast cancer, indicating its potential role in the regulation of miRNAs. The miR-155 inhibits the expression of the VHL (von Hippel-Lindau tumor suppressor) gene and increases expression of pro-angiogenic factors such as VEGF. In addition, the results indicated that loss of VHL in breast cancer can be attributed to a high expression of miR-155. This study aims to evaluate the effect of melatonin in modulation of miR-155 expression involved in angiogenesis of breast cancer in the cell lineage MDA-MB-231, treated or not with melatonin, besides the analysis of the miR-155 expression and its target gene by real time PCR. The results may determine the possible relationship between melatonin and miR-155 and its role in the genesis of new blood vessels, and thus establish potential therapeutic protocols for control of this cellular event, crucial for a worse prognosis in patients with breast cancer.
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