Miat and interacting protein Metadherin maintain a stem-like niche to promote medulloblastoma tumorigenesis and treatment resistance.

Long noncoding RNAs (lncRNAs) play essential roles in the development and progression of many cancers. However, the contributions of lncRNAs to medulloblastoma (MB) remain poorly understood. Here, we identify Miat as an lncRNA enriched in the sonic hedgehog group of MB that is required for maintenance of a treatment-resistant stem-like phenotype in the disease. Loss of Miat results in the differentiation of tumor-initiating, stem-like MB cells and enforces the differentiation of tumorigenic stem-like MB cells into a nontumorigenic state. Miat expression in stem-like MB cells also facilitates treatment resistance by down-regulating p53 signaling and impairing radiation-induced cell death, which can be reversed by therapeutic inhibition of Miat using antisense oligonucleotides. Mechanistically, the RNA binding protein Metadherin (Mtdh), previously linked to resistance to cytotoxic therapy in cancer, binds to Miat in stem-like MB cells. Like the loss of Miat, the loss of Mtdh reduces tumorigenicity and increases sensitivity to radiation-induced death in stem-like MB cells. Moreover, Miat and Mtdh function to regulate the biogenesis of several microRNAs and facilitate tumorigenesis and treatment resistance. Taken together, these data reveal an essential role for the lncRNA Miat in sustaining a treatment-resistant pool of tumorigenic stem-like MB cells.

p53-intact cancers escape tumor suppression through loss of long noncoding RNA Dino.

Many long noncoding RNA (lncRNA) genes exist near cancer-associated loci, yet evidence connecting lncRNA functions to recurrent genetic alterations in cancer are lacking. Here, we report that DINO, the lncRNA transcribed from the cancer-associated DINO/CDKN1A locus, suppresses tumor formation independent of p21, the protein encoded at the locus. Loss of one or two alleles of Dino impairs p53 signaling and apoptosis, resulting in a haplo-insufficient tumor suppressor phenotype in genetically defined mouse models of tumorigenesis. A discrete region of the DINO/CDKN1A locus is recurrently hypermethylated in human cancers, silencing DINO but not CDKN1A, the gene encoding p21. Hypermethylation silences DINO, impairs p53 signaling pathway in trans, and is mutually exclusive with TP53 alterations, indicating that DINO and TP53 comprise a common tumor suppressor module. Therefore, DINO encodes a lncRNA essential for tumor suppression that is recurrently silenced in human cancers as a mechanism to escape p53-dependent tumor suppression.

DNA Demethylation by DNMT3A and DNMT3B in vitro and of Methylated Episomal DNA in Transiently Transfected Cells.

The DNA methylation program in vertebrates is an essential part of the epigenetic regulatory cascade of development, cell differentiation, and progression of diseases including cancer. While the DNA methyltransferases (DNMTs) are responsible for the in vivo conversion of cytosine (C) to methylated cytosine (5mC), demethylation of 5mC on cellular DNA could be accomplished by the combined action of the ten-eleven translocation (TET) enzymes and DNA repair. Surprisingly, the mammalian DNMTs also possess active DNA demethylation activity in vitro in a Ca2+- and redox conditions-dependent manner, although little is known about its molecular mechanisms and occurrence in a cellular context. In this study, we have used LC-MS/MS to track down the fate of the methyl group removed from 5mC on DNA by mouse DNMT3B in vitro and found that it becomes covalently linked to the DNA methylation catalytic cysteine of the enzyme. We also show that Ca2+ homeostasis-dependent but TET1/TET2/TET3/TDG-independent demethylation of methylated episomal DNA by mouse DNMT3A or DNMT3B can occur in transfected human HEK 293 and mouse embryonic stem (ES) cells. Based on these results, we present a tentative working model of Ca2+ and redox conditions-dependent active DNA demethylation by DNMTs. Our study substantiates the potential roles of the vertebrate DNMTs as double-edged swords in DNA methylation-demethylation during Ca2+-dependent physiological processes.

Self-hydrogenated shell promoting photocatalytic H2 evolution on anatase TiO2.

As one of the most important photocatalysts, TiO2 has triggered broad interest and intensive studies for decades. Observation of the interfacial reactions between water and TiO2 at microscopic scale can provide key insight into the mechanisms of photocatalytic processes. Currently, experimental methodologies for characterizing photocatalytic reactions of anatase TiO2 are mostly confined to water vapor or single molecule chemistry. Here, we investigate the photocatalytic reaction of anatase TiO2 nanoparticles in water using liquid environmental transmission electron microscopy. A self-hydrogenated shell is observed on the TiO2 surface before the generation of hydrogen bubbles. First-principles calculations suggest that this shell is formed through subsurface diffusion of photo-reduced water protons generated at the aqueous TiO2 interface, which promotes photocatalytic hydrogen evolution by reducing the activation barrier for H2 (H-H bond) formation. Experiments confirm that the self-hydrogenated shell contains reduced titanium ions, and its thickness can increase to several nanometers with increasing UV illuminance.

TET1 suppresses cancer invasion by activating the tissue inhibitors of metalloproteinases.

Tumor suppressor gene silencing through cytosine methylation contributes to cancer formation. Whether DNA demethylation enzymes counteract this oncogenic effect is unknown. Here, we show that TET1, a dioxygenase involved in cytosine demethylation, is downregulated in prostate and breast cancer tissues. TET1 depletion facilitates cell invasion, tumor growth, and cancer metastasis in prostate xenograft models and correlates with poor survival rates in breast cancer patients. Consistently, enforced expression of TET1 reduces cell invasion and breast xenograft tumor formation. Mechanistically, TET1 suppresses cell invasion through its dioxygenase and DNA binding activities. Furthermore, TET1 maintains the expression of tissue inhibitors of metalloproteinase (TIMP) family proteins 2 and 3 by inhibiting their DNA methylation. Concurrent low expression of TET1 and TIMP2 or TIMP3 correlates with advanced node status in clinical samples. Together, these results illustrate a mechanism by which TET1 suppresses tumor development and invasion partly through downregulation of critical gene methylation.

Breast cancer cells induce stromal fibroblasts to secrete ADAMTS1 for cancer invasion through an epigenetic change.

Microenvironment plays an important role in cancer development. We have reported that the cancer-associated stromal cells exhibit phenotypic and functional changes compared to stromal cells neighboring to normal tissues. However, the molecular mechanisms as well as the maintenance of these changes remain elusive. Here we showed that through co-culture with breast cancer cells for at least three to four passages, breast normal tissue-associated fibroblasts (NAFs) gained persistent activity for promoting cancer cell invasion, partly via up-regulating ADAM metallopeptidase with thrombospondin type 1 motif, 1 (ADAMTS1). Furthermore, we demonstrated that the DNA methylation pattern in the ADAMTS1 promoter has no alteration. Instead, the loss of EZH2 binding to the ADAMTS1 promoter and the resulting decrease of promoter-associated histone H3K27 methylation may account for the up-regulation of ADAMTS1. Importantly, the lack of EZH2 binding and the H3K27 methylation on the ADAMTS1 promoter were sustained in cancer cell-precocultured NAFs after removal of cancer cells. These results suggest that cancer cells are capable of inducing stromal fibroblasts to secrete ADAMTS1 persistently for their invasion and the effect is epigenetically inheritable.