Omega-3 polyunsaturated fatty acids eicosapentaenoic acid and docosahexaenoic acid enhance dexamethasone sensitivity in multiple myeloma cells by the p53/miR-34a/Bcl-2 axis

Dexamethasone is widely used in multiple myeloma (MM) for its cytotoxic effects on lymphoid cells. However, many MM patients are resistant to dexamethasone, although some can benefit from dexamethasone treatment. In this study, we noted that ω-3 polyunsaturated fatty acids (PUFAs) enhanced the dexamethasone sensitivity of MM cells by inducing cell apoptosis. q-PCR analysis revealed that miR-34a could be significantly induced by PUFAs in U266 and primary MM cells. Transfection with miR-34a antagonist or miR-34a agomir could restore or suppress the dexamethasone sensitivity in U266 cells. Both luciferase reporter assay and Western blot showed that Bcl-2 is the direct target of miR-34a in MM cells. In addition, we observed that PUFAs induced p53 protein expression in MM cells under dexamethasone administration. Furthermore, suppressing p53 by its inhibitor, Pifithrin-α, regulated the miR-34a expression and modulated the sensitivity to dexamethasone in U266 cells. In summary, these results suggest that PUFAs enhance dexamethasone sensitivity to MM cells through the p53/miR-34a axis with a likely contribution of Bcl-2 suppression.     

Restoration of p53/miR-34a regulatory axis decreases survival advantage and ensures Bax-dependent apoptosis of non-small cell lung carcinoma cells

Tumor-suppressive miR-34a, a direct target of p53, has been shown to target several molecules of cell survival pathways. Here, we show that capsaicin-induced oxidative DNA damage culminates in p53 activation to up-regulate expression of miR-34a in non-small cell lung carcinoma (NSCLC) cells. Functional analyses further indicate that restoration of miR-34a inhibits B cell lymphoma-2 (Bcl-2) protein expression to withdraw the survival advantage of these resistant NSCLC cells. In such a proapoptotic cellular milieu, where drug resistance proteins are also down-regulated, p53-transactivated Bcl-2 associated X protein (Bax) induces apoptosis via the mitochondrial death cascade. Our results suggest that p53/miR-34a regulatory axis might be critical in sensitizing drug-resistant NSCLC cells.     

Inhibition of Intestinal Epithelial Apoptosis Improves Survival in a Murine Model of Radiation Combined Injury

World conditions place large populations at risk from ionizing radiation (IR) from detonation of dirty bombs or nuclear devices. In a subgroup of patients, ionizing radiation exposure would be followed by a secondary infection. The effects of radiation combined injury are potentially more lethal than either insult in isolation. The purpose of this study was to determine mechanisms of mortality and possible therapeutic targets in radiation combined injury. Mice were exposed to IR with 2.5 Gray (Gy) followed four days later by intratracheal methicillin-resistant Staphylococcus aureus (MRSA). While either IR or MRSA alone yielded 100% survival, animals with radiation combined injury had 53% survival (p = 0.01). Compared to IR or MRSA alone, mice with radiation combined injury had increased gut apoptosis, local and systemic bacterial burden, decreased splenic CD4 T cells, CD8 T cells, B cells, NK cells, and dendritic cells, and increased BAL and systemic IL-6 and G-CSF. In contrast, radiation combined injury did not alter lymphocyte apoptosis, pulmonary injury, or intestinal proliferation compared to IR or MRSA alone. In light of the synergistic increase in gut apoptosis following radiation combined injury, transgenic mice that overexpress Bcl-2 in their intestine and wild type mice were subjected to IR followed by MRSA. Bcl-2 mice had decreased gut apoptosis and improved survival compared to WT mice (92% vs. 42%; p<0.01). These data demonstrate that radiation combined injury results in significantly higher mortality than could be predicted based upon either IR or MRSA infection alone, and that preventing gut apoptosis may be a potential therapeutic target.     

新型microRNA—miR-34在肿瘤中的研究进展

miR-34是一类保守的、非编码miRNA。人类miR-34包括miR-34a、miR-34b和miR-34c等,在多种肿瘤中都呈现非正常表达。miR-34通过被p53激活,抑制E2F3、Bcl-2、c—myc、CDK4、CDK6、Cyclin D1以及Cyclin E2的表达,使肿瘤细胞停滞在G1期,抑制肿瘤细胞的生长,诱导肿瘤细胞凋亡,并通过E2F3、SIRT1与p53形成正反馈环路,不断增强其自身和p53的作用。本文就miR-34的研究进展进行综述。     

miR-34a-5p was involved in chronic intermittent hypoxia-induced autophagy of human coronary artery endothelial cells via Bcl-2/beclin 1 signal transduction pathway

Autophagy refers to the genetically regulated process to regulate the survival and death of cells, which is conserved in evolution. Typically, autophagy exerts a vital part under physiopathological conditions. Whether autophagy can be resulted from chronic intermittent hypoxia (CIH), a prominent characteristic of obstructive sleep apnea-hypopnea syndrome (OSAHS), remains to be investigated. Furthermore, microRNAs (miRNAs) can serve as the regulating factors in a variety of benign and malignant diseases; nonetheless, it remains to be fully illustrated about the way by which miRNAs modulate autophagy. According to our results, for human coronary artery endothelial cells (HCAECs), CIH increased the expression of autophagy-associated proteins, which depended on the concentration and time; besides, it could promote autophagic vacuole (AV) formation. In addition, CIH could activate beclin 1, which was dependent on dose and time. In HCAECs, microRNA-34a-5p (miR-34a-5p) was overexpressed after exposed to CIH, and its target protein B-cell lymphoma 2 (Bcl-2) was downregulated. Moreover, inhibiting miR-34a-5p increased Bcl-2 and p62 expression, while downregulating beclin 1, Vps34, Atg5, and LC3 levels, implying the role of miR-34a-5p in CIH-induced autophagy. Moreover, exogenous upregulation of Bcl-2 could block miR-34a-5p influence on CIH-induced autophagy through suppressing beclin 1 expression. Additionally, beclin 1 could enhance the autophagy induced by CIH. In conclusion, overexpression of miR-34a-5p activated beclin 1 through Bcl-2 inhibition in CIH and participated in CIH-induced autophagy.     

miR-300 regulates cellular radiosensitivity through targeting p53 and apaf1 in human lung cancer cells

microRNAs (miRNAs) play a crucial role in mediation of the cellular sensitivity to ionizing radiation (IR). Previous studies revealed that miR-300 was involved in the cellular response to IR or chemotherapy drug. However, whether miR-300 could regulate the DNA damage responses induced by extrinsic genotoxic stress in human lung cancer and the underlying mechanism remain unknown. In this study, the expression of miR-300 was examined in lung cancer cells treated with IR, and the effects of miR-300 on DNA damage repair, cell cycle arrest, apoptosis and senescence induced by IR were investigated. It was found that IR induced upregulation of endogenous miR-300, and ectopic expression of miR-300 by transfected with miR-300 mimics not only greatly enhanced the cellular DNA damage repair ability but also substantially abrogated the G2 cell cycle arrest and apoptosis induced by IR. Bioinformatic analysis predicted that p53 and apaf1 were potential targets of miR-300, and the luciferase reporter assay showed that miR-300 significantly suppressed the luciferase activity through binding to the 3′-UTR of p53 or apaf1 mRNA. In addition, overexpression of miR-300 significantly reduced p53/apaf1 and/or IR-induced p53/apaf1 protein expression levels. Flow cytomertry analysis and colony formation assay showed that miR-300 desensitized lung cancer cells to IR by suppressing p53-dependent G2 cell cycle arrest, apoptosis and senescence. These data demonstrate that miR-300 regulates the cellular sensitivity to IR through targeting p53 and apaf1 in lung cancer cells.     

Intact p53-Dependent Responses in miR-34-Deficient Mice

MicroRNAs belonging to the miR-34 family have been proposed as critical modulators of the p53 pathway and potential tumor suppressors in human cancers. To formally test these hypotheses, we have generated mice carrying targeted deletion of all three members of this microRNA family. We show that complete inactivation of miR-34 function is compatible with normal development in mice. Surprisingly, p53 function appears to be intact in miR-34-deficient cells and tissues. Although loss of miR-34 expression leads to a slight increase in cellular proliferation in vitro, it does not impair p53-induced cell cycle arrest or apoptosis. Furthermore, in contrast to p53-deficient mice, miR-34-deficient animals do not display increased susceptibility to spontaneous, irradiation-induced, or c-Myc-initiated tumorigenesis. We also show that expression of members of the miR-34 family is particularly high in the testes, lungs, and brains of mice and that it is largely p53-independent in these tissues. These findings indicate that miR-34 plays a redundant function in the p53 pathway and suggest additional p53-independent functions for this family of miRNAs.     

MicroRNA-34a regulation of endothelial senescence

Endothelial senescence is thought to play a role in cardiovascular diseases such as atherosclerosis. We hypothesized that endothelial microRNAs (miRNAs) regulate endothelial survival and senescence. We found that miR-34a is highly expressed in primary endothelial cells. We observed that miR-34a expression increases in senescent human umbilical cord vein endothelial cells (HUVEC) and in heart and spleen of older mice. MiR-34a over-expression induces endothelial cell senescence and also suppresses cell proliferation by inhibiting cell cycle progression. Searching for how miR-34a affects senescence, we discovered that SIRT1 is a target of miR-34a. Over-expressing miR-34a inhibits SIRT1 protein expression, and knocking down miR-34a enhances SIRT1 expression. MiR-34a triggers endothelial senescence in part through SIRT1, since forced expression of SIRT1 blocks the ability of miR-34a to induce senescence. Our data suggest that miR-34a contributes to endothelial senescence through suppression of SIRT1.     

miR-34a在幼鼠海马神经元细胞增殖和凋亡中的作用

目的:探讨miR-34a在幼鼠海马神经元细胞增殖凋亡中的作用。方法:分离幼鼠海马神经元细胞,转染miR-34a抑制剂(miR-34a inhibitor)、抑制剂对照(inhibitor control)、miR-34a模拟物(miR-34a mimics)、模拟物对照(mimics control),RT-PCR检测细胞中miR-34a表达水平。MTT检测转染后细胞增殖情况。流式细胞仪检测细胞凋亡情况。Western blot检测细胞中Cleaved-caspase-3、Bcl-2、Bax的表达水平。结果:转染miR-34a inhibitor可以抑制miR-34a的表达,miR-34a mimics可以促进miR-34a的表达。miR-34a mimics对细胞增殖抑制率明显高于mimics control组(P0.05),miR-34a inhibitor组抑制率明显低于inhibitor control组(P0.05)。miR-34a inhibitor组神经元细胞凋亡率明显低于inhibitor control组(P0.05),miR-34a mimics组神经元细胞凋亡率明显高于mimics control组(P0.01),inhibitor control组和mimics control组神经元细胞凋亡率差异不显著(P0.05)。miR-34a inhibitor组Cleaved-caspase-3、Bax蛋白表达量低于inhibitor control组,差异显著(P0.05);miR-34a inhibitor组Bcl-2蛋白表达量高于inhibitor control组,差异显著(P0.05);miR-34a mimics组Cleaved-caspase-3、Bax蛋白表达量高于mimics control,差异显著(P0.05);miR-34a mimics组Bcl-2蛋白表达量低于mimics control,差异显著(P0.05)。结论:miR-34a抑制海马神经元细胞增殖,促进细胞凋亡,其作用机制可能与调控Cleaved-caspase-3、Bcl-2、Bax表达有关。     

microRNA-34a promotes DNA damage and mitotic catastrophe

Efficient and error-free DNA repair is critical for safeguarding genome integrity, yet it is also linked to radio- and chemoresistance of malignant tumors. miR-34a, a potent tumor suppressor, influences a large set of p53-regulated genes and contributes to p53-mediated apoptosis. However, the effects of miR-34a on the processes of DNA damage and repair are not entirely understood. We explored tet-inducible miR-34a-expressing human p53 wild-type and R273H p53 mutant GBM cell lines, and found that miR-34a influences the broad spectrum of 53BP1-mediated DNA damage response. It escalates both post-irradiation and endogenous DNA damage, abrogates radiation-induced G₂/M arrest and drastically increases the number of irradiated cells undergoing mitotic catastrophe. Furthermore, miR-34a downregulates 53BP1 and inhibits its recruitment to the sites of DNA double-strand breaks. We conclude that whereas miR-34a counteracts DNA repair, it also contributes to the p53-independent elimination of distressed cells, thus preventing the rise of genomic instability in tumor cell populations. These properties of miR-34a can potentially be exploited for DNA damage-effecting therapies of malignancies.     

Interdependent regulation of p53 and miR-34a in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) has an incidence 4/100 000 people in the western world and is one of the first cancers reported to be associated with deregulated miRNA expression. microRNAs are small non coding RNAs that are important regulators of protein expression through binding to their untranslated 3'-UTR region. The miR-34 family was demonstrated to be induced by the tumor suppressor p53 and to elicit p53-like responses like senescence, cell cycle arrest and apoptosis depending on the cell type. We have shown in a recent paper that miR-34a is severely increased in the TCL1-mouse model of CLL. This finding was reflected in human CLL. Moreover, it is demonstrated that its expression is dependent on the presence of the SNP309 in the intronic promoter of the MDM2 gene. In addition, low miR-34a expression was associated with shorter time to treatment (log-rank P = 0.003) in CLL. When reintroduced into CLL cells, miR-34a was able to induce apoptosis. Interestingly, this was dependent on an intact p53 pathway. Here, we present data showing that knockdown of p53 in HCT-116 cells severely reduces miR-34a induced apoptosis. In conclusion, miR-34a is proposed as a marker for the activity of the p53 pathway in CLL.     

miR-34家族——-肿瘤抑制蛋白p53高度相关microRNA

若干微小RNA(microRNA, miRNA)与肿瘤抑制蛋白p53高度相关, 其中miR-34家族最具代表性。一方面p53可通过对miR-34家族的调控实现对多个原癌基因如Bcl-2、c-myc以及细胞因子如cyclinE2、cyclinD1和c-Met的抑制, 进而发挥抑癌作用; 另一方面miR-34家族也可以通过抑制沉默信息调节子SIRTI来进一步增强p53的活性。p53与miR-34家族之间形成的正反馈调节网络对抑制肿瘤的发生发展及恶化均起着重要的作用。文章对p53高度相关的miR-34家族在肿瘤发生发展及治疗的最新进展作一论述。