Argonaute CLIP Defines a Deregulated miR-122-Bound Transcriptome that Correlates with Patient Survival in Human Liver Cancer - PubMed (original) (raw)

Argonaute CLIP Defines a Deregulated miR-122-Bound Transcriptome that Correlates with Patient Survival in Human Liver Cancer

Joseph M Luna et al. Mol Cell. 2017.

Abstract

MicroRNA-122, an abundant and conserved liver-specific miRNA, regulates hepatic metabolism and functions as a tumor suppressor, yet systematic and direct biochemical elucidation of the miR-122 target network remains incomplete. To this end, we performed Argonaute crosslinking immunoprecipitation (Argonaute [Ago]-CLIP) sequencing in miR-122 knockout and control mouse livers, as well as in matched human hepatocellular carcinoma (HCC) and benign liver tissue to identify miRNA target sites transcriptome-wide in two species. We observed a majority of miR-122 binding on 3' UTRs and coding exons followed by extensive binding to other genic and non-genic sites. Motif analysis of miR-122-dependent binding revealed a G-bulged motif in addition to canonical motifs. A large number of miR-122 targets were found to be species specific. Upregulation of several common mouse and human targets, most notably BCL9, predicted survival in HCC patients. These results broadly define the molecular consequences of miR-122 downregulation in hepatocellular carcinoma.

Keywords: Argonaute; BCL9; CLIP; HCC; Wnt; gene regulation; hepatocellular carcinoma; miR-122.

Copyright © 2017 Elsevier Inc. All rights reserved.

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Figures

Figure 1

Figure 1

Non-canonical and widespread binding of miR-122 targets in mouse liver. (A) Example miR-122 dependent binding peak defined by CLIP signal in WT livers that is absent in KO. (B) Motif enrichment analysis of peaks resembling (A). (C) Canonical miR-122 motif enrichment by Ago peak position for loci resembling (A) compared to all observed peaks. Inset depicts canonical binding target interactions. (D) Non-canonical bulged miR-122 motif enrichment by Ago peak position for loci resembling (A) compared to all observed peaks. Inset depicts proposed non-canonical binding target interactions. (E) Summary of mRNA target loci distributed among the top 30 (lower pie) or the top 10 miRNA families in mouse liver (upper pie). (F) Global annotation of miRNA target loci as defined in (E). Int: intergenic. Number of loci per category indicated in parentheses. L2FC, Log-2 fold change. See also Figure S1.

Figure 2

Figure 2

Functional characterization of the miR-122 bound transcriptome. (A-B) Scatterplot with marginal histograms comparing log2 fold change in CLIP binding and RNAseq expression between WT and KO livers for all 3’UTR loci containing canonical (red) or non-canonical (blue) miR-122-5p binding events, compared to top 10 miRNA targets exclusive of miR-122 (grey). (B) Boxplots per genomic region depicting log2 fold change in CLIP binding between WT and KO livers. (C) Boxplots per genomic region depicting log2 fold change in RNAseq expression between WT and KO livers. (D) Mean PhyloP conservation scores across the core 6mer for miR-122 seed targets compared to seeds from the top miRNA families by genomic annotation. (E) Mouse to human seed sequence level comparison of unique CLIP peaks per top 10 miRNA families by all targets, 3’UTR targets, or CDS targets. Dashed lines indicate percentage of miR-122 seed sites conserved between mouse and humans in CLIP data, and the white line indicates average for top miRNAs. ****P<0.0001, ns P>0.05, two-sided Mann-Whitney U-test. See also Figures S1–S3.

Figure 3

Figure 3

AGO-CLIP of human HCC displays features of miR-122 loss. (A) Cumulative density function (CDF) of the log2 fold change in CLIP binding between normal adjacent and matched tumor tissue for all 3’UTR targets containing indicated miRNA seeds by family, from nine donors. “All” refers to the top 50 miRNA families, inclusive of miR-122 and miR-21. (B) Boxplots per genomic region depicting log2 fold change in CLIP binding between normal adjacent and matched tumor tissue. (C) Mean log2 fold change in CLIP binding per patient plotted against miR-122 relative abundance as measured by qPCR. Pearson correlation of best-fit line is shown. (D) Overlap among all primary miR-122 target genes found in mice and humans. Pie charts depict expression level proportion from RNAseq in miR-122 KO mouse livers relative to WT livers. ****P<0.0001, ns P>0.05, two-sided Mann-Whitney U-test. See also Figures S4–S5.

Figure 4

Figure 4

Higher expression of select miR-122 targets in human HCC is associated with poor survival. (A) Consensus-clustered heat map of shared human and mouse miR-122 target genes (n = 965) in LIHC tumors (n = 373 patients) from TCGA reveals general upregulation of miR-122 targets. (B) Expression Z-scores for BCL9, SLC52A2 and STX6 by sample type. (C) RSEM expression for miR-122 and targets BCL9, SLC52A2 and STX6 per tumor sample. Regression coefficients of best-fit line and significance P-values are shown. (D) Kaplan-Meier survival analysis of LIHC patients displaying upregulated versus non-altered levels of genes in (B) with indicated log-rank test P-values, hazard ratios (HR), and confidence intervals. *,P<0.001, K–S test. See also Figure S6.

Figure 5

Figure 5

BCL9 is a conserved, non-canonical exonic target of miR-122 and is implicated in human HCC. (A–B) Ago-CLIP binding profile (A) and RNaseq expression (B) of the Bcl9, Slc52A2, or Stx6 genes in WT and KO mice. miR-122 sites labeled in black triangles. (C) qPCR of BCL9 levels from mouse (Hepa1-6) or human (SNU449) hepatoma cells following 25nM control (NC) or miR-122 mimic (122) treatment for 48 hours. *P<0.05, two-tailed t-test. All data are represented as mean ± standard deviation (error bars).

Figure 6

Figure 6

Luciferase validation of Slc52a2, Stx6, and Bcl9 as mouse and human conserved miR-122 targets. (A–B) Luciferase reporter assay of mouse and human conserved (C) Slc52a2 and (D) Stx6. Renilla luciferase activity was normalized to Firefly luciferase (RLU) after transfection with miR-122 mimic or NC scrambled RNA. (E) Luciferase reporter measurements of human or mouse BCL9 miR-122 sites, tested individually. Dashed line indicates respective signal for mutated sites). Mouse and human alignments are shown. *P<0.05, two-tailed t-test. All data are represented as mean ± standard deviation (error bars). See also Figure S7.

Figure 7

Figure 7

miR-122 modulates β-catenin dependent transcription by suppressing BCL9. (A) FLAG-tagged human BCL9 expression levels in 293T cells after transfection with 50nM control (NC) or miR-122 mimic (122). WT BCL9 is compared to a mutant where all 6 exonic miR-122 sites were mutated while preserving amino acid sequence. (B) β-catenin dependent activity measured in MHCC-LM3 transfected with 50nM control (NC) or miR-122 mimic (122). TOP/FOP luciferase reporters and WT or MUT BCL9 constructs were transfected 12 hours after miRNA transfection and measured after 48 hours. Firefly luciferase activity was normalized to Renilla luciferase. For immunoblots, fold change (F.C.) represents the protein level normalized to that of NC treated cells. (C) Expression of the downstream targets of Wnt signaling (e.g. CD44 and c-JUN) determined in MHCC-LM3 shBCL9 knockdown cells via qPCR. (D) qPCR expression of targets in (C) in WT, miR-122 knockout (122KO), or miR-122 and BCL9 double knockout (DKO) Huh7.5 cells. (E) Cell viability assay of MHCCC-LM3 cells under BCL9 knockdown or overexpression conditions. (F) Cell viability assay of Huh7.5 cell mutants in (D) upon BCL9 rescue expression (*P<0.05, two-tailed t-test). All data are represented as mean ± standard deviation (error bars). See also Figure S7.

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