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Epigenetic inactivation of the 5-methylcytosine RNA methyltransferase NSUN7 is associated with clinical outcome and therapeutic vulnerability in liver cancer

ABSTRACT: RNA modifications are important regulators of transcript activity and an increasingly emerging body of data suggest that the epitranscriptome and its associated enzymes are altered in human tumors. In this study, the initial screening for genetic and epigenetic defects of 5-methylcytosine RNA methyltransferases in tranformed cell lines, identified the NOL1/NOP2/Sun domain family member 7 (NSUN7) as undergoing promoter CpG island hypermethylation-associated transcriptional silencing in a cancer-specific manner. NSUN7 epigenetic inactivation was common in liver malignant cells and we coupled bisulfite conversion of cellular RNA with next-generation sequencing (bsRNA-seq) to found the RNA targets of this poorly characterized putative methyltransferase. Using knock-out and restoration-of-function models, we observed that the mRNA of the coiled-coil domain containing 9B (CCDC9B) gene required NSUN7-mediated methylation for transcript instability. Most important, proteomics analyses determined that CCDC9B loss impaired protein levels of its partner, the MYC-regulator Influenza Virus NS1A Binding Protein (IVNS1ABP), creating sensitivity to bromodomain inhibitors in those liver cancer cells exhibiting NSUN7 epigenetic silencing. The DNA methylation-associated loss of NSUN7 was also observed in primary liver tumors where it was associated with poor overall survival and an immune-like signature, providing a potential attractive therapeutic niche for the current use of immune checkpoint inhibitors in hepatocellular carcinoma.

INSTRUMENT(S): Orbitrap Eclipse

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Liver, Epithelial Cell

DISEASE(S): Hepatocellular Carcinoma

SUBMITTER: Joan Josep Bech-Serra

LAB HEAD: Manel Esteller

PROVIDER: PXD038422 | Pride | 2023-05-10

REPOSITORIES: Pride

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Project description:Epigenetic inheritance is the transmission of information independently of the nucleotide sequence of the genome. A fundamental question in biology is to what extent does epigenetics contribute to trans-generational inheritance. Here we investigate the role of Argonaute-small-RNA pathways in epigenetic inheritance in the nematode C. elegans. Argonautes present their guide RNAs for base-pairing with target sequences and, upon binding, can cleave the target RNA and/or recruit cofactors that mediate post-transcriptional or transcriptional silencing 1,2. Previous studies have shown that Argonaute small-RNA pathways reinforce and maintain epigenetic silencing in C. elegans 3-5. For example, the conserved PIWI-related Argonaute PRG-1 initiates a remarkably stable mode of epigenetic silencing, termed RNA-induced epigenetic silencing (RNAe) 3. Alleles that are silenced by RNAe send trans-acting Argonaute-small-RNA signals that can act in a sequence-specific manner to induce the permanent Epigenetic inheritance is the transmission of information independently of the nucleotide sequence of the genome. A fundamental question in biology is to what extent does epigenetics contribute to trans-generational inheritance. Here we investigate the role of Argonaute-small-RNA pathways in epigenetic inheritance in the nematode C. elegans. Argonautes present their guide RNAs for base-pairing with target sequences and, upon binding, can cleave the target RNA and/or recruit cofactors that mediate post-transcriptional or transcriptional silencing 1,2. Previous studies have shown that Argonaute small-RNA pathways reinforce and maintain epigenetic silencing in C. elegans 3-5. For example, the conserved PIWI-related Argonaute PRG-1 initiates a remarkably stable mode of epigenetic silencing, termed RNA-induced epigenetic silencing (RNAe) 3. Alleles that are silenced by RNAe send trans-acting Argonaute-small-RNA signals that can act in a sequence-specific manner to induce the permanent silencing of homologous genes 3. Here we explore an opposite phenomenon, RNA-induced gene activation (RNAa), in which an expressed gene provides a sequence-specific signal that can activate a silent homologous gene. We provide evidence that the CSR-1 Argonaute is required for this trans-activating signal. CSR-1 engages antisense small RNAs complementary to most, if not all, germline-expressed mRNAs 6,7. Moreover, we show that the ability of a foreign sequence to mediate RNAa is correlated with acquisition of CSR-1-associated small RNAs targeting the foreign sequence. Thus CSR-1 small RNAs constitute a memory of previous germline-gene expression that protects endogenous genes from epigenetic silencing. These findings reveal a remarkably sophisticated epigenetic surveillance mechanism that monitors the flow of transgenerational information ensuring that progeny express only those genes also expressed in their parents. Examine small RNA population changes in different transgene lines

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Epigenetic inactivation of the 5-methylcytosine RNA methyltransferase NSUN7 is associated with clinical outcome and therapeutic vulnerability in liver cancer

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