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KRAS-driven miR-29b Expression is Required for Tumor Suppressor Gene Silencing

ABSTRACT: KRAS activation drives DNA methylation and silencing of specific tumor suppressor genes (TSGs). We previously showed that the ERK pathway induces transcriptional repression of TET1, which results in conversion of TSG promoters from a hydroxymethylated, active state to a hypermethylated and silenced state. Here we identified miR-29b as a KRAS-induced molecule that represses TET1 expression. In KRAS-transformed cells, ectopic miR-29b inhibition restores expression of TET1, thereby reactivating TSGs by reducing methylation and restoring hydroxymethylation. Mining gene expression data of lung cancer cell lines identified additional TSGs suppressed by KRAS signaling whose expression was restored by inhibition of miR-29b and re-expression of TET1. Because KRAS changes TSG promoters from hydroxymethylated to hypermethylated with miR-29b-dependent silencing of TET1, we demonstrate a model in which DNMT1 is present on target promoters prior to KRAS transformation. We also propose miR-29b as a potential circulating biomarker and target for rational treatment of specific malignancies.

ORGANISM(S): synthetic construct Homo sapiens

PROVIDER: GSE100857 | GEO | 2017/07/31

SECONDARY ACCESSION(S): PRJNA393300

REPOSITORIES: GEO

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Project description:Tissue fibrosis is a significant health issue associated with organ dysfunction and failure. Increased deposition of collagen and other extracellular matrix (ECM) proteins in the interstitial area is a major process in the formation of tissue fibrosis. The microRNA-29 (miR-29) family has been demonstrated as anti-fibrotic microRNAs. Our recent work also showed that dysregulation of miR-29 contributes to the formation of cardiac fibrosis in animal models of uremic cardiomyopathy and replenish of miR-29 attenuated cardiac fibrosis in these animals. However, due to the multi-targeting effect, overexpression of miR-29 could result in unexpected side effect. In the current study, we constructed a novel col1a1-miR-29b vector using collagen 1a1 promoter, which can strategically express miR-29b-3p (miR-29b) in cells with high expression of collagen and thus minimize the side effect of excessive miR-29b. Because of the similarity between the col1a1 promoter in the plasmid and the endogenous col1a1 promoter in the cell, pro-fibrotic factors that stimulate endogenous collagen expression will simultaneously activate the col1a1 promoter in the plasmid vector and thus stimulate the anti-fibrotic miR-29b expression. The increased miR-29b will then contra-regulate the collagen synthesis and maintain a dynamic balance of collagen. To evaluate the anti-fibrotic effect of miR-29b overexpression, we performed RNA sequencing in MEF cells transfected with the col1a1-miR-29b vector with or without TGF-β treatment. A CMV-miR-29b vector was used as positive control. The RNA-sequencing data showed that TGF-β treatment upregulated a broad spectrum of extracellular matrix (ECM) genes. In accordance, the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis using GAGE package showed that the top 5 upregulated pathways after TGF-β treatment were mostly fibrosis-related, including focal adhesion, ECM reaction, and TGF-β signaling pathways, while transfection of miR-29b expression vectors attenuated the activation of these pathways, suggesting their anti-fibrotic effect. However, despite that the expression of miR-29b in CMV-miR-29b transfected cells were about 1000 times higher compared to the col1a1-miR-29b transfected cells, there was no significant difference in the anti-fibrotic effect in these cells. In summary, our work demonstrated that the col1a1-miR-29b vector expresses much lower miR-29b compared to the CMV-miR-29b vector, but it is as effective as the CMV-miR-29b vector in blocking the fibrosis-related signaling pathways in response to TGF-β treatment. Our results also suggest that miR-29b has a moderate effect on each of its targeting genes, and its anti-fibrotic effect may result from perturbation of a broad spectrum of fibrosis-related signaling pathways.

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KRAS-driven miR-29b Expression is Required for Tumor Suppressor Gene Silencing

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