BackgroundMicroRNAs (miRNAs) are small, non-coding RNAs (20–24 nucleotides) that post-transcriptionally modulate gene expression by negatively regulating the stability or translational efficiency of their target mRNAs. The aim of this study was to investigate the expression pattern of microRNA-26b (miR-26b) in human breast cancer, and its potential role in disease pathogenesis.MethodsQuantitative reverse transcription-polymerase chain reaction (qRT-PCR) was performed to determine the expression level of miR-26b in 38 breast cancer specimens and adjacent normal breast tissues. MTT assays were conducted to explore the impact of miR-26b overexpression on the proliferation of human MDA-MB-231 breast cancer cells. Luciferase reporter assays were employed to validate regulation of a putative target of miR-26b. The effect of modulating miR-26b on endogenous levels of this target were subsequently confirmed via qRT-PCR and Western blot.ResultsMiR-26b expression was relatively decreased in breast cancer specimens compared with adjacent normal tissues (P<0.01). Overexpression of miR-26b suppressed MDA-MB-231 cell growth. Luciferase assays using a reporter carrying a putative miR-26b target site in the 3' untranslated region of PTGS2 revealed that miR-26b directly targets PTGS2. Overexpression of miR-26b led to downregulation of PTGS2 at the mRNA and protein level, as assessed by qRT-PCR and Western blot. Targeted knockdown of PTGS2 by siRNA significantly inhibited the proliferation of MDA-MB-231 breast cancer cells.ConclusionsMiR-26b may act as a tumor suppressor in breast cancer. The overexpression of miR-26b inhibits cellular growth by targeting PTGS2, suggesting its use as a potential therapeutic target for breast cancer.

The receptor-interacting protein 1 (RIPK1)/RIPK3 kinases play important roles in necroptosis that is closely linked to inflammatory response. Although the activation of necroptosis is well characterized, how necroptosis is tuned down is largely unknown. Here, we found that Parkin (also known as PARK2 ), an E3 ubiquitin ligase implicated in Parkinson’s disease and a tumor suppressor, regulates necroptosis and inflammation by regulating necrosome formation. Parkin prevents the formation of the RIPK1-RIPK3 complex by promoting polyubiquitination of RIPK3. Parkin is phosphorylated and activated by the cellular energy sensor AMP-activated protein kinase (AMPK). Parkin-deficiency potentiates the RIPK1-RIPK3 interaction, RIPK3 phosphorylation, and necroptosis. Importantly, Parkin deficiency enhances inflammation and inflammation-associated tumorigenesis. These findings demonstrate that the AMPK-Parkin axis negatively regulates necroptosis via inhibiting the RIPK1-RIPK3 complex formation and this regulation may serve as an important mechanism to fine-tune necroptosis and inflammation.

MicroRNAs (miRNAs) are a class of highly conserved, small endogenous single-strand non-coding RNAs. They are aberrantly expressed in the circulation and tissue of patients with cancer. Therefore, it has been suggested that they may act as key regulators of carcinogenesis. The aim of the present study was to examine the expression level of miR-195-5p in human breast cancer and its potential role in carcinogenesis. The expression level of miR-195-5p was measured in 40 breast cancer specimens and adjacent normal breast tissues by quantitative polymerase chain reaction (qPCR). Next, to explore the potential function of miR-195-5p, we used MDA-MB-231 human breast cancer cells and carried out MTT, colony formation, Transwell chamber migration and cell cycle assays. The dual-luciferase reporter assay was also performed to determine putative targets of miR-195-5p, which were validated using qPCR and western blot assays. We found that miR-195-5p expression was significantly decreased in the 40 breast cancer specimens when compared with that in the adjacent normal breast tissues (P<0.05). Overexpression of miR-195-5p inhibited cell proliferation, reduced cell colony formation, suppressed cell migration and caused an accumulation of cells in the G1 phase of the cell cycle. In the 3′-untranslated region (3′-UTR) of cyclin E1 (CCNE1), we found two putative target sites which may bind miR-195-5p, suggesting that CCNE1 is a direct target of miR-195-5p. Furthermore, through qPCR and western blot assays we showed that overexpression of miR-195-5p reduced CCNE1 mRNA and protein levels, respectively. Our study suggests that miR-195-5p may act as a tumor suppressor in breast cancer. Therefore, targeting of this miRNA may provide a novel strategy for the diagnosis and treatment of patients with this lethal disease.