MiR‐376a suppresses the proliferation and invasion of non‐small‐cell lung cancer by targeting c‐Myc

It has been reported that miR‐376a is involved in the formation and progression of several types of cancer. However, the expression and function of miR‐376a is still unknown in non‐small cell lung carcinomas (NSCLC). In this study, the expression of miR‐376a in NSCLC tissues and cell lines were examined by real‐time PCR, the effects of miR‐376a on cell proliferation, apoptosis and invasion were evaluated in vitro. Luciferase reporter assay was performed to identify the targets of miR‐376a. The results showed that miR‐376a was significantly downregulated in NSCLC tissues and cell lines. Restoration of miR‐376a in NSCLC cell line A549 significantly inhibited cell proliferation, increased cell apoptosis and suppressed cell invasion, compared with control‐transfected A549 cells. Luciferase reporter assay showed that c‐Myc, an oncogene that regulating cell survival, angiogenesis and metastasis, was a direct target of miR‐376a. Over‐expression of miR‐376a decreased the mRNA and protein levels of c‐Myc in A549 cells. In addition, upregulation of c‐Myc inhibited miR‐376a‐induced inhibition of cell proliferation and invasion in A549 cells. Therefore, our results indicate a tumor suppressor role of miR‐376a in NSCLC by targeting c‐Myc. miR‐376a may be a promising therapeutic target for NSCLC.     

LncRNA‐MIF,a c‐Myc‐activated long non‐coding RNA,suppresses glycolysis by promoting Fbxw7‐mediated c‐Myc degradation

The c‐Myc proto‐oncogene is activated in more than half of all human cancers. However, the precise regulation of c‐Myc protein stability is unknown. Here, we show that the lncRNA‐MIF (c‐Myc inhibitory factor), a c‐Myc‐induced long non‐coding RNA, is a competing endogenous RNA for miR‐586 and attenuates the inhibitory effect of miR‐586 on Fbxw7, an E3 ligase for c‐Myc, leading to increased Fbxw7 expression and subsequent c‐Myc degradation. Our data reveal the existence of a feedback loop between c‐Myc and lncRNA‐MIF, through which c‐Myc protein stability is finely controlled. Additionally, we show that the lncRNA‐MIF inhibits aerobic glycolysis and tumorigenesis by suppressing c‐Myc and miR‐586.     

Myc‐regulated microRNAs attenuate embryonic stem cell differentiation

Myc proteins are known to have an important function in stem cell maintenance. As Myc has been shown earlier to regulate microRNAs (miRNAs) involved in proliferation, we sought to determine whether c‐Myc also affects embryonic stem (ES) cell maintenance and differentiation through miRNAs. Using a quantitative primer‐extension PCR assay we identified miRNAs, including, miR‐141, miR‐200, and miR‐429 whose expression is regulated by c‐Myc in ES cells, but not in the differentiated and tumourigenic derivatives of ES cells. Chromatin immunoprecipitation analyses indicate that in ES cells c‐Myc binds proximal to genomic regions encoding the induced miRNAs. We used expression profiling and seed homology to identify genes specifically downregulated both by these miRNAs and by c‐Myc. We further show that the introduction of c‐Myc‐induced miRNAs into murine ES cells significantly attenuates the downregulation of pluripotency markers on induction of differentiation after withdrawal of the ES cell maintenance factor LIF. In contrast, knockdown of the endogenous miRNAs accelerate differentiation. Our data show that in ES cells c‐Myc acts, in part, through a subset of miRNAs to attenuate differentiation.     

Che‐1 is targeted by c‐Myc to sustain proliferation in pre‐B‐cell acute lymphoblastic leukemia

Despite progress in treating B‐cell precursor acute lymphoblastic leukemia (BCP‐ALL), disease recurrence remains the main cause of treatment failure. New strategies to improve therapeutic outcomes are needed, particularly in high‐risk relapsed patients. Che‐1/AATF (Che‐1) is an RNA polymerase II‐binding protein involved in proliferation and tumor survival, but its role in hematological malignancies has not been clarified. Here, we show that Che‐1 is overexpressed in pediatric BCP‐ALL during disease onset and at relapse, and that its depletion inhibits the proliferation of BCP‐ALL cells. Furthermore, we report that c‐Myc regulates Che‐1 expression by direct binding to its promoter and describe a strict correlation between Che‐1 expression and c‐Myc expression. RNA‐seq analyses upon Che‐1 or c‐Myc depletion reveal a strong overlap of the respective controlled pathways. Genomewide ChIP‐seq experiments suggest that Che‐1 acts as a downstream effector of c‐Myc. These results identify the pivotal role of Che‐1 in the control of BCP‐ALL proliferation and present the protein as a possible therapeutic target in children with relapsed BCP‐ALL.     

AMPK promotes survival of c‐Myc‐positive melanoma cells by suppressing oxidative stress

Although c‐Myc is essential for melanocyte development, its role in cutaneous melanoma, the most aggressive skin cancer, is only partly understood. Here we used the Nras^Q61KINK4a^?/? mouse melanoma model to show that c‐Myc is essential for tumor initiation, maintenance, and metastasis. c‐Myc‐expressing melanoma cells were preferentially found at metastatic sites, correlated with increased tumor aggressiveness and high tumor initiation potential. Abrogation of c‐Myc caused apoptosis in primary murine and human melanoma cells. Mechanistically, c‐Myc‐positive melanoma cells activated and became dependent on the metabolic energy sensor AMP‐activated protein kinase (AMPK), a metabolic checkpoint kinase that plays an important role in energy and redox homeostasis under stress conditions. AMPK pathway inhibition caused apoptosis of c‐Myc‐expressing melanoma cells, while AMPK activation protected against cell death of c‐Myc‐depleted melanoma cells through suppression of oxidative stress. Furthermore, TCGA database analysis of early‐stage human melanoma samples revealed an inverse correlation between C‐MYC and patient survival, suggesting that C‐MYC expression levels could serve as a prognostic marker for early‐stage disease.     

Effects of siRNA Targeting c‐Myc and VEGF on Human Colorectal Cancer Volo Cells

c‐Myc and vascular endothelial growth factor (VEGF) genes are frequently deregulated and overexpressed in this malignancy, and strategies designed to inhibit c‐Myc and VEGF expression in cancer cells may have considerable therapeutic value. In the present study, we design and use short interfering RNA (siRNA) to inhibit c‐Myc and VEGF expression in colorectal cancer Volo cells and validate their effects on cell proliferation, cell cycle, apoptosis, and cell metastasis. Upon transient transfection with plasmid‐encoding siRNA, it was found that expression of c‐Myc and VEGF was significantly downregulated in siRNA‐transfected cells and the downregulation of c‐Myc and VEGF inhibited cell growth and induced apoptosis and metastasis of Volo cells. c‐Myc and VEGF downregulation also increased cell population in the G0–G1 phase. In conclusion, the specific siRNA efficiently silenced the expression of c‐Myc and VEGF, further suppressed the cell proliferation, triggered cell apoptosis, and inhibited cell invasiveness of colorectal cancer Volo cells. © 2012 Wiley Periodicals, Inc. J Biochem Mol Toxicol 26:499‐505, 2012;Viewthis article online at wileyonlinelibrary.com . DOI 10.1002/jbt.21455     

LncRNA HOXA11‐AS promotes hepatocellular carcinoma progression by repressing miR‐214‐3p

Accumulating studies supported that lncRNAs played important roles in tumorigenesis. LncRNA HOXA11‐AS was a novel lncRNA that has been proved to involved in several tumours. However, the role of HOXA11‐AS in the development of hepatocellular carcinoma (HCC) remains to be explained. In our study, we showed that HOXA11‐AS expression was up‐regulated in the HCC tissues, and the higher expression of HOXA11‐AS was associated with the advanced stage in the HCC samples. In addition, we indicated that the expression of HOXA11‐AS was up‐regulated in HCC cell lines (Hep3B, SMMC‐7721, MHCC97‐H and BEL‐7402) compared with normal liver cell lines (HL‐7702). Overexpression of HOXA11‐AS promoted HCC proliferation and invasion and induced the epithelial‐mesenchymal transition (EMT) and knockdown of HOXA11‐AS suppressed the HCC cell proliferation and invasion. However, we showed that miR‐214‐3p expression was down‐regulated in the HCC tissues and cell lines. Ectopic expression of miR‐214‐3p suppressed HCC cell proliferation and invasion. Furthermore, we indicated that overexpression of HOXA11‐AS decreased the miR‐214‐3p expression and the expression of miR‐214‐3p was negatively related with the HOXA11‐AS expression in HCC samples. Ectopic expression of HOXA11‐AS increased HCC proliferation and invasion and induced EMT through inhibiting miR‐214‐3p expression. These data suggested that HOXA11‐AS/miR‐214‐3p axis was responsible for development of HCC.     

MicroRNA‐876‐5p inhibits cell proliferation,migration and invasion by targeting c‐Met in osteosarcoma

Recently, aberrant expression of miR‐876‐5p has been reported to participate in the progression of several human cancers. However, the expression and function of miR‐876‐5p in osteosarcoma (OS) are still unknown. Here, we found that the expression of miR‐876‐5p was significantly down‐regulated in OS tissues compared to para‐cancerous tissues. Clinical association analysis indicated that underexpression of miR‐876‐5p was positively correlated with advanced clinical stage and poor differentiation. More importantly, OS patients with low miR‐876‐5p level had a significant shorter overall survival compared to miR‐876‐5p high‐expressing patients. In addition, gain‐ and loss‐of‐function experiments demonstrated that miR‐876‐5p restoration suppressed whereas miR‐876‐5p knockdown promoted cell proliferation, migration and invasion in both U2OS and MG63 cells. In vivo studies revealed that miR‐876‐5p overexpression inhibited tumour growth of OS in mice. Mechanistically, miR‐876‐5p reduced c‐Met abundance in OS cells and inversely correlated c‐Met expression in OS tissues. Herein, c‐Met was recognized as a direct target of miR‐876‐5p using luciferase reporter assay. Notably, c‐Met restoration rescued miR‐876‐5p attenuated the proliferation, migration and invasion of OS cells. In conclusion, these findings indicate that miR‐876‐5p may be used as a potential therapeutic target and promising biomarker for the diagnosis and prognosis of OS.     

Pleiotrophin,a target of miR‐384, promotes proliferation,metastasis and lipogenesis in HBV‐related hepatocellular carcinoma

Hepatitis B virus (HBV) infection plays a crucial role and is a major cause of hepatocellular carcinoma (HCC) in China. microRNAs (miRNAs) have emerged as key players in hepatic steatosis and carcinogenesis. We found that down‐regulation of miR‐384 expression was a common event in HCC, especially HBV‐related HCC. However, the possible function of miR‐384 in HBV‐related HCC remains unclear. The oncogene pleiotrophin (PTN) was a target of miR‐384. HBx inhibited miR‐384, increasing PTN expression. The PTN receptor N‐syndecan was highly expressed in HCC. PTN induced by HBx acted as a growth factor via N‐syndecan on hepatocytes and further promoted cell proliferation, metastasis and lipogenesis. PTN up‐regulated sterol regulatory element‐binding protein 1c (SREBP‐1c) through the N‐syndecan/PI3K/Akt/mTORC1 pathway and the expression of lipogenic genes, including fatty acid synthesis (FAS). PTN‐mediated de novo lipid synthesis played an important role in HCC proliferation and metastasis. PI3K/AKT and an mTORC1 inhibitor diminished PTN‐induced proliferation, metastasis and lipogenesis. Taken together, these data strongly suggest that the dysregulation of miR‐384 could play a crucial role in HBV related to HCC, and the target gene of miR‐384, PTN, represents a new potential therapeutic target for the prevention of hepatic steatosis and further progression to HCC after chronic HBV infection.