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Yang K.R.,Cellular and Molecular Medicine Program | Mooney S.M.,James Buchanan Brady Urological Institute | Zarif J.C.,James Buchanan Brady Urological Institute | Coffey D.S.,James Buchanan Brady Urological Institute | And 3 more authors.
Journal of Cellular Biochemistry | Year: 2014

Cancer cells can be described as an invasive species that is able to establish itself in a new environment. The concept of niche construction can be utilized to describe the process by which cancer cells terraform their environment, thereby engineering an ecosystem that promotes the genetic fitness of the species. Ecological dispersion theory can then be utilized to describe and model the steps and barriers involved in a successful diaspora as the cancer cells leave the original host organ and migrate to new host organs to successfully establish a new metastatic community. These ecological concepts can be further utilized to define new diagnostic and therapeutic areas for lethal cancers. 115: 1478-1485, 2014. © 2014 Wiley Periodicals, Inc. © 2014 Wiley Periodicals, Inc. Source


Navarro F.,Cellular and Molecular Medicine Program | Lieberman J.,Cellular and Molecular Medicine Program | Lieberman J.,Harvard University
PLoS ONE | Year: 2015

MiR-34, a tumor suppressor miRNA family transcriptionally activated by p53, is considered a critical mediator of p53 function. However, knockout of the mouse miR-34 family has little or no effect on the p53 response. The relative contribution of different miR-34 family members to p53 function or how much p53 relies on miR-34 in human cells is unclear. Here we show that miR-34a has a complex effect on the p53 response in human cells. In HCT116 cells miR-34a overexpression enhances p53 transcriptional activity, but the closely related family members, miR-34b and miR-34c, even when over-expressed, have little effect. Both TP53 itself and MDM4, a strong p53 transactivation inhibitor, are direct targets of miR-34a. The genes regulated by miR-34a also include four other post-translational inhibitors of p53. miR-34a overexpression leads to variable effects on p53 levels in p53-sufficient human cancer cell lines. In HCT116, miR-34a overexpression increases p53 protein levels and stability. About a quarter of all mRNAs that participate in the human p53 network bind to biotinylated miR-34a, suggesting that many are direct miR-34a targets. However, only about a fifth of the mRNAs that bind to miR-34a also bind to miR-34b or miR-34c. Two human cell lines knocked out for miR-34a have unimpaired p53-mediated responses to genotoxic stress, like mouse cells. The complex positive and negative effects of miR-34 on the p53 network suggest that rather than simply promoting the p53 response, miR-34a might act at a systems level to stabilize the robustness of the p53 response to genotoxic stress. Copyright: © 2015 Navarro, Lieberman. Source


Tay Y.,Beth Israel Deaconess Medical Center | Tan S.M.,Cellular and Molecular Medicine Program | Tan S.M.,Harvard University | Karreth F.A.,Beth Israel Deaconess Medical Center | And 4 more authors.
Cell Reports | Year: 2014

Tumor suppressor genes (TSGs) are often concomitantly lost or mutated in human cancers and have been shown to act synergistically to promote tumorigenesis. In addition to genomic alterations, posttranscriptional regulation by microRNAs (miRNAs) represents another mechanism by which TSG expression is dysregulated in cancers. Although miRNAs that target critical TSGs such as PTEN or p53 have been identified, little is known about miRNAs that concomitantly regulate both these key TSGs. In this study, we characterize microRNA 518c* (miR-518c*) and miR-638 as dual PTEN- and p53-targeting miRNAs that are upregulated in multiple human cancers. We focus on miR-638 and show that it associates independently with these two tumor suppressor transcripts as well as BRCA1, a known miR-638 target. We find that miR-638 overexpression promotes tumorigenesis and demonstrate cooperativity between miR-638 and its host gene Dnm2, suggesting that the Dnm2 locus encodes two distinct oncogenic components that play important roles in tumorigenesis. © 2014 The Authors. Source


Ivanov P.,Brigham and Womens Hospital | Ivanov P.,Harvard University | O'Day E.,Cellular and Molecular Medicine Program | O'Day E.,Harvard University | And 8 more authors.
Proceedings of the National Academy of Sciences of the United States of America | Year: 2014

Angiogenin (ANG) is a stress-activated ribonuclease that promotes the survival of motor neurons. Ribonuclease inactivating point mutations are found in a subset of patients with ALS, a fatal neurodegenerative disease with no cure. We recently showed that ANG cleaves tRNA within anticodon loops to produce 5′- and 3′-fragments known as tRNA-derived, stress-induced RNAs (tiRNAs). Selected 5′-tiRNAs (e.g., tiRNAAla, tiRNACys) cooperate with the translational repressor Y-box binding protein 1 (YB-1) to displace the cap-binding complex eIF4F from capped mRNA, inhibit translation initiation, and induce the assembly of stress granules (SGs). Here, we show that translationally active tiRNAs assemble unique G-quadruplex (G4) structures that are required for translation inhibition. We show that tiRNAAla binds the cold shock domain of YB-1 to activate these translational reprogramming events. We discovered that 5′-tiDNAAla (the DNA equivalent of 5′-tiRNAAla) is a stable tiRNA analog that displaces eIF4F from capped mRNA, inhibits translation initiation, and induces the assembly of SGs. The 5′-tiDNAAla also assembles a G4 structure that allows it to enter motor neurons spontaneously and trigger a neuroprotective response in a YB-1-dependent manner. Remarkably, the ability of 5′-tiRNAAla to induce SG assembly is inhibited by G4 structures formed by pathological GGGGCC repeats found in C9ORF72, the most common genetic cause of ALS, suggesting that functional interactions between G4 RNAs may contribute to neurodegenerative disease. © 2014, National Academy of Sciences. All rights reserved. Source


Tan S.M.,Cellular and Molecular Medicine Program | Tan S.M.,Harvard University | Kirchner R.,Harvard University | Jin J.,New England Biolabs | And 6 more authors.
Cell Reports | Year: 2014

Identifying microRNA (miRNA)-regulated genes is key to understanding miRNA function. However, many miRNA recognition elements (MREs) do not follow canonical "seed" base-pairing rules, making identification of bona fide targets challenging. Here, we apply an unbiased sequencing-based systems approach to characterize miR-522, a member of the oncogenic primate-specific chromosome 19 miRNA cluster, highly expressed in poorly differentiated cancers. To identify miRNA targets, we sequenced full-length transcripts captured by a biotinylated miRNA mimic. Within these targets, mostly noncanonical MREs were identified by sequencing RNase-resistant fragments. miR-522 overexpression reduced mRNA, protein levels, and luciferase activity of >70% of a random list of candidate target genes and MREs. Bioinformatic analysis suggested that miR-522 regulates cell proliferation, detachment, migration, and epithelial-mesenchymal transition. miR-522 induces G1 cell-cycle arrest and causes cells to detach without anoikis, become invasive, and express mesenchymal genes. Thus, our method provides a simple but effective technique for identifying miRNA-regulated genes and biological function. © 2014 The Authors. Source

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