Aurora Esquela-Kerscher

Oncomirs - microRNAs with a role in cancer.

MicroRNAs (miRNAs) are an abundant class of small non-protein-coding RNAs that function as negative gene regulators. They regulate diverse biological processes, and bioinformatic data indicates that each miRNA can control hundreds of gene targets, underscoring the potential influence of miRNAs on almost every genetic pathway. Recent evidence has shown that miRNA mutations or mis-expression correlate with various human cancers and indicates that miRNAs can function as tumour suppressors and oncogenes. miRNAs have been shown to repress the expression of important cancer-related genes and might prove useful in the diagnosis and treatment of cancer.

The let-7 MicroRNA Represses Cell Proliferation Pathways in Human Cells

MicroRNAs play important roles in animal development, cell differentiation, and metabolism and have been implicated in human cancer. The let-7 microRNA controls the timing of cell cycle exit and terminal differentiation in Caenorhabditis elegans and is poorly expressed or deleted in human lung tumors. Here, we show that let-7 is highly expressed in normal lung tissue, and that inhibiting let-7 function leads to increased cell division in A549 lung cancer cells. Overexpression of let-7 in cancer cell lines alters cell cycle progression and reduces cell division, providing evidence that let-7 functions as a tumor suppressor in lung cells. let-7 was previously shown to regulate the expression of the RAS lung cancer oncogenes, and our work now shows that multiple genes involved in cell cycle and cell division functions are also directly or indirectly repressed by let-7. This work reveals the let-7 microRNA to be a master regulator of cell proliferation pathways.

The let-7 microRNA reduces tumor growth in mouse models of lung cancer

MicroRNAs have been increasingly implicated in human cancer and interest has grown about the potential to use microRNAs to combat cancer. Lung cancer is the most prevalent form of cancer worldwide and lacks effective therapies. Here we have used both in vitro and in vivo approaches to show that the let-7 microRNA directly represses cancer growth in the lung. We find that let-7 inhibits the growth of multiple human lung cancer cell lines in culture, as well as the growth of lung cancer cell xenografts in immunodeficient mice. Using an established orthotopic mouse lung cancer model, we show that intranasal let-7 administration reduces tumor formation in vivo in the lungs of animals expressing a G12D activating mutation for the K-ras oncogene. These findings provide direct evidence that let-7 acts as a tumor suppressor gene in the lung and indicate that this miRNA may be useful as a novel therapeutic agent in lung cancer.

The mir-34 microRNA is required for the DNA damage response in vivo in C. elegans and in vitro in human breast cancer cells

MicroRNAs (miRNAs) are important regulators of cell fate determination and homeostasis. Expression of these small RNA genes is tightly regulated during development and in normal tissues, but they are often misregulated in cancer. MiRNA expression is also affected by DNA damaging agents, such as radiation. In particular, mammalian miR-34 is upregulated by p53 in response to radiation, but little is known about the role of this miRNA in vivo. Here we show that Caenorhabditis elegans with loss-of-function mutations in the mir-34 gene have an abnormal cellular survival response to radiation; these animals are highly radiosensitive in the soma and radioresistant in the germline. These findings show a role for mir-34 in both apoptotic and non-apoptotic cell death in vivo, much like that of cep-1, the C. elegans p53 homolog. These results have been additionally validated in vitro in breast cancer cells, wherein exogenous addition of miR-34 alters cell survival post-radiation. These observations confirm that mir-34 is required for a normal cellular response to DNA damage in vivo resulting in altered cellular survival post-irradiation, and point to a potential therapeutic use for anti-miR-34 as a radiosensitizing agent in p53-mutant breast cancer.

Reciprocal expression of lin-41 and the microRNAs let-7 and mir-125 during mouse embryogenesis.

In C. elegans, heterochronic genes control the timing of cell fate determination during development. Two heterochronic genes, let‐7 and lin‐4, encode microRNAs (miRNAs) that down‐regulate a third heterochronic gene lin‐41 by binding to complementary sites in its 3′UTR. let‐7 and lin‐4 are conserved in mammals. Here we report the cloning and sequencing of mammalian lin‐41 orthologs. We find that mouse and human lin‐41 genes contain predicted conserved complementary sites for let‐7 and the lin‐4 ortholog, mir‐125, in their 3′UTRs. Mouse lin‐41 (Mlin‐41) is temporally expressed in developing mouse embryos, most dramatically in the limb buds. Mlin‐41 is down‐regulated during mid‐embryogenesis at the time when mouse let‐7c and mir‐125 RNA levels are up‐regulated. Our results suggest that mammalian lin‐41 is temporally regulated by miRNAs in order to direct key developmental events such as limb formation. Developmental Dynamics 234:1046–1054, 2005.

Post-embryonic expression of C. elegans microRNAs belonging to the lin-4 and let-7 families in the hypodermis and the reproductive system.

MicroRNAs (miRNAs) are regulatory molecules that negatively control gene expression by binding to complementary sequences on target mRNAs. The most thoroughly characterized miRNAs, lin‐4 and let‐7, direct cell fate determination during the larval transitions in C. elegans and act as key regulators of temporal gene expression. lin‐4 and let‐7 are founding members of two distinct families of miRNA genes sharing strong sequence homology primarily in the 5′ end of the mature miRNAs. In this report, we characterize the temporal and spatial expression patterns of lin‐4 and let‐7 family members using northern blot analysis and mir::gfp fusion studies. Our results show that lin‐4 and let‐7 homologues possess distinct temporal and spatial expression patterns during nematode development and that known heterochronic genes regulate their expression. We find that certain lin‐4 and let‐7 family members display overlapping expression patterns in the hypodermis and the reproductive system, suggesting that combinations of miRNAs from across families may control common developmental events. Developmental Dynamics 234:868–877, 2005.

miR-888 is an expressed prostatic secretions- derived microRNA that promotes prostate cell growth and migration

microRNAs (miRNAs) are a growing class of small non-coding RNAs that exhibit widespread dysregulation in prostate cancer. We profiled miRNA expression in syngeneic human prostate cancer cell lines that differed in their metastatic potential in order to determine their role in aggressive prostate cancer. miR-888 was the most differentially expressed miRNA observed in human metastatic PC3-ML cells relative to non-invasive PC3-N cells, and its levels were higher in primary prostate tumors from cancer patients, particularly those with seminal vesicle invasion. We also examined a novel miRNA-based biomarker source called expressed prostatic secretions in urine (EPS urine) for miR-888 expression and found that its levels were preferentially elevated in prostate cancer patients with high-grade disease. These expression studies indicated a correlation for miR-888 in disease progression. We next tested how miR-888 regulated cancer-related pathways in vitro using human prostate cancer cell lines. Overexpression of miR-888 increased proliferation and migration, and conversely inhibition of miR-888 activity blocked these processes. miR-888 also increased colony formation in PC3-N and LNCaP cells, supporting an oncogenic role for this miRNA in the prostate. Our data indicates that miR-888 functions to promote prostate cancer progression and can suppress protein levels of the tumor suppressor genes RBL1 and SMAD4. This miRNA holds promise as a diagnostic tool using an innovative prostatic fluid source as well as a therapeutic target for aggressive prostate cancer.

The age of high-throughput microRNA profiling

New advancements in microarray technology offer a stepping-stone to the biological function of microRNAs.

GDF11 induces kidney fibrosis, renal cell epithelial-to-mesenchymal transition, and kidney dysfunction and failure

Background: GDF11 modulates embryonic patterning and kidney organogenesis. Herein, we sought to define GDF11 function in the adult kidney and in renal diseases. Methods: In vitro renal cell lines, genetic, and murine in vivo renal injury models were examined. Results: Among tissues tested, Gdf11 was highest in normal adult mouse kidney. Expression was increased acutely after 5/6 nephrectomy, ischemia‐reperfusion injury, kanamycin toxicity, or unilateral ureteric obstruction. Systemic, high‐dose GDF11 administration in adult mice led to renal failure, with accompanying kidney atrophy, interstitial fibrosis, epithelial‐to‐mesenchymal transition of renal tubular cells, and eventually death. These effects were associated with phosphorylation of SMAD2 and could be blocked by follistatin. In contrast, Gdf11 heterozygous mice showed reduced renal Gdf11 expression, renal fibrosis, and expression of fibrosis‐associated genes both at baseline and after unilateral ureteric obstruction compared with wild‐type littermates. The kidney‐specific consequences of GDF11 dose modulation are direct effects on kidney cells. GDF11 induced proliferation and activation of NRK49f renal fibroblasts and also promoted epithelial‐to‐mesenchymal transition of IMCD‐3 tubular epithelial cells in a SMAD3‐dependent manner. Conclusion: Taken together, these data suggest that GDF11 and its downstream signals are critical in vivo mediators of renal injury. These effects are through direct actions of GDF11 on renal tubular cells and fibroblasts. Thus, regulation of GDF11 presents a therapeutic target for diseases involving renal fibrosis and impaired tubular function.

Characterization and Evidence of the miR-888 Cluster as a Novel Cancer Network in Prostate

Prostate cancer afflicts 1 in 7 men and is the second leading cause of male cancer-related deaths in the United States. MicroRNAs (miRNAs), an extensive class of approximately 22 nucleotide noncoding RNAs, are often aberrantly expressed in tissues and fluids from prostate cancer patients, but the mechanisms of how specific miRNAs regulate prostate tumorigenesis and metastasis are poorly understood. Here, miR-888 was identified as a novel prostate factor that promotes proliferation and migration. miR-888 resides within a genomic cluster of 7 miRNA genes (mir-892c, mir-890, mir-888, mir-892a, mir-892b, mir-891b, mir-891a) on human chromosome Xq27.3. Moreover, as miR-888 maps within HPCX1, a locus associated with susceptibility and/or hereditary prostate cancer, it was hypothesized that additional miRNA cluster members also play functional roles in the prostate. Expression analysis determined that cluster members were similarly elevated in metastatic PC3-ML prostate cells and their secreted exosomes, as well as enriched in expressed prostatic secretions urine-derived exosomes obtained from clinical patients with high-grade prostate cancer. In vitro assays revealed that miR-888 cluster members selectively modulated PC3-derived and LNCaP cell proliferation, migration, invasion, and colony formation. Mouse xenograft studies verified miR-888 and miR-891a as pro-oncogenic factors that increased prostate tumor growth in vivo. Further analysis validated RBL1, KLF5, SMAD4, and TIMP2 as direct miR-888 targets and that TIMP2 is also coregulated by miR-891a. This study provides the first comprehensive analysis of the entire miR-888 cluster and reveals biological insight. Implications: This work reveals a complex noncoding RNA network in the prostate that could be developed as effective diagnostic and therapeutic tools for advanced prostate cancer. Mol Cancer Res; 16(4); 669–81. ©2018 AACR.