Over the past several years it has become clear that alterations in the expression of microRNA (miRNA) genes contribute to the pathogenesis of most — if not all — human malignancies. These alterations can be caused by various mechanisms, including deletions, amplifications or mutations involving miRNA loci, epigenetic silencing or the dysregulation of transcription factors that target specific miRNAs. Because malignant cells show dependence on the dysregulated expression of miRNA genes, which in turn control or are controlled by the dysregulation of multiple protein-coding oncogenes or tumour suppressor genes, these small RNAs provide important opportunities for the development of future miRNA-based therapies.

/pdf/causes-and-consequences-of-microrna-dysregulation-in-cancer-1oe9jwwj8l.pdf

Causes and consequences of microRNA dysregulation in cancer

Blinded by the Light: The Growing Complexity of p53

MYC on the Path to Cancer

https://cdr.lib.unc.edu/downloads/tm70mx374

Integrated Genomic Characterization of Papillary Thyroid Carcinoma

MicroRNAs (miRNAs) are small noncoding RNAs that typically inhibit the translation and stability of messenger RNAs (mRNAs), controlling genes involved in cellular processes such as inflammation, cell-cycle regulation, stress response, differentiation, apoptosis, and migration. Thus, miRNAs have been implicated in the regulation of virtually all signaling circuits within a cell, and their dysregulation has been shown to play an essential role in the development and progression of cancer. Here, after a brief description of miRNA genomics, biogenesis, and function, we discuss the effects of miRNA dysregulation in the cellular pathways that lead to the progressive conversion of normal cells into cancer cells and the potential to develop new molecular miRNA-targeted therapies.

MicroRNAs in cancer.

MicroRNAs (miRNAs) are ∼22 nucleotide non-coding RNA molecules that regulate gene expression post-transcriptionally. Although aberrant expression of miRNAs in various human cancers suggests a role for miRNAs in tumorigenesis, it remains largely unclear as to whether knockdown of a specific miRNA affects tumor growth. In this study, we profiled miRNA expression in matched normal breast tissue and breast tumor tissues by TaqMan real-time polymerase chain reaction miRNA array methods. Consistent with previous findings, we found that miR-21 was highly overexpressed in breast tumors compared to the matched normal breast tissues among 157 human miRNAs analysed. To better evaluate the role of miR-21 in tumorigenesis, we transfected breast cancer MCF-7 cells with anti-miR-21 oligonucleotides and found that anti-miR-21 suppressed both cell growth in vitro and tumor growth in the xenograft mouse model. Furthermore, this anti-miR-21-mediated cell growth inhibition was associated with increased apoptosis and decreased cell proliferation, which could be in part owing to downregulation of the antiapoptotic Bcl-2 in anti-miR-21-treated tumor cells. Together, these results suggest that miR-21 functions as an oncogene and modulates tumorigenesis through regulation of genes such as bcl-2 and thus, it may serve as a novel therapeutic target.

miR-21-mediated tumor growth

MicroRNA-21 targets the tumor suppressor gene tropomyosin 1 (TPM1)

MicroRNAs (miRNAs) are a class of naturally occurring small non-coding RNAs that target protein-coding mRNAs at the post-transcriptional level. Our previous studies suggest that mir-21 functions as an oncogene and has a role in tumorigenesis, in part through regulation of the tumor suppressor gene tropomyosin 1 (TPM1). Given that TPM1 has been implicated in cell migration, in this study we further investigated the role of mir-21 in cell invasion and tumor metastasis. We found that suppression of mir-21 in metastatic breast cancer MDA-MB-231 cells significantly reduced invasion and lung metastasis. Consistent with this, ectopic expression of TPM1 remarkably reduced cell invasion. Furthermore, we identified two additional direct mir-21 targets, programmed cell death 4 (PDCD4) and maspin, both of which have been implicated in invasion and metastasis. Like TPM1, PDCD4 and maspin also reduced invasiveness of MDA-MB-231 cells. Finally, the expression of PDCD4 and maspin inversely correlated with mir-21 expression in human breast tumor specimens, indicating the potential regulation of PDCD4 and maspin by mir-21 in these tumors. Taken together, the results suggest that, as an oncogenic miRNA, mir-21 has a role not only in tumor growth but also in invasion and tumor metastasis by targeting multiple tumor/metastasis suppressor genes. Therefore, suppression of mir-21 may provide a novel approach for the treatment of advanced cancers.

/pdf/microrna-21-targets-tumor-suppressor-genes-in-invasion-and-chyih46yhp.pdf

MicroRNA-21 targets tumor suppressor genes in invasion and metastasis

The tumor suppressor p53 negatively regulates a number of genes, including the proto-oncogene c-Myc, in addition to activating many other genes. One mechanism of the p53-mediated c-Myc repression may involve transcriptional regulation. However, it is not clear whether microRNAs (miRNAs) play a role in the p53-mediated posttranscriptional regulation of c-Myc. In this study, we show that a putative tumor suppressor, miR-145, is expressed through the phosphoinositide-3 kinase (PI-3K)/Akt and p53 pathways. Importantly, p53 transcriptionally induces the expression of miR-145 by interacting with a potential p53 response element (p53RE) in the miR-145 promoter. We further show that c-Myc is a direct target for miR-145. Although miR-145 silences the expression of c-Myc, anti-miR-145 enhances its expression. This specific silencing of c-Myc by miR-145 accounts at least in part for the miR-145-mediated inhibition of tumor cell growth both in vitro and in vivo. Finally, the blockade of miR-145 by anti-miR-145 is able to reverse the p53-mediated c-Myc repression. Together, these results define the role of miR-145 in the posttranscriptional regulation of c-Myc by p53 and suggest that, as a new member of the p53 regulatory network, miR-145 provides a direct link between p53 and c-Myc in this gene regulatory network.

https://www.pnas.org/content/pnas/106/9/3207.full.pdf

p53 represses c-Myc through induction of the tumor suppressor miR-145

MicroRNAs (miRNAs) are endogenous, small, non-coding RNAs, which are capable of silencing gene expression at the post-transcriptional level. In this study, we report that miR-205 is significantly underexpressed in breast tumor compared to the matched normal breast tissue. Similarly, breast cancer cell lines, including MCF-7 and MDA-MB-231, express a lower level miR-205 than the non-malignant MCF-10A cells. Of interest, ectopic expression of miR-205 significantly inhibits cell proliferation and anchorage independent growth, as well as cell invasion. Furthermore, miR-205 was shown to suppress lung metastasis in an animal model. Finally, western blot combined with the luciferase reporter assays demonstrate that ErbB3 and vascular endothelial growth factor A (VEGF-A) are direct targets for miR-205, and this miR-205-mediated suppression is likely through the direct interaction with the putative miR-205 binding site in the 3′-untranslated region (3′-UTR) of ErbB3 and VEGF-A. Together, these results suggest that miR-205 is a tumor suppressor in breast cancer.

/pdf/suppression-of-cell-growth-and-invasion-by-mir-205-in-breast-46nezwrc7m.pdf

Hailong Wu

Papers

miR-21-mediated tumor growth

MicroRNA-21 targets the tumor suppressor gene tropomyosin 1 (TPM1)

MicroRNA-21 targets tumor suppressor genes in invasion and metastasis

p53 represses c-Myc through induction of the tumor suppressor miR-145

Suppression of cell growth and invasion by miR-205 in breast cancer