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Modulation of miR-29 Expression by Alpha-fetoprotein is linked to the Hepatocellular Carcinoma Epigenome

ABSTRACT: Globally, hepatocellular carcinoma (HCC) accounts for 70-85% of primary liver cancers and ranks second in the leading cause of male cancer death. Serum alpha-fetoprotein (AFP), normally highly expressed in the liver only during fetal development, is reactivated in 60% of HCC tumors and associated with poor patient outcome. We hypothesize that AFP+ and AFP- tumors differ biologically. Using microarray-based global microRNA profiling in 223 HCC patients, we found that members of the miR-29 family were the most significantly (p<0.001) down-regulated miRNAs in AFP+ tumors. Consistent with miR-29's role in targeting DNA methyltransferase 3A (DNMT3A), a key enzyme regulating DNA methylation, we found a significant inverse correlation (p<0.001) between miR-29 and DNMT3A gene expression suggesting that they might be functionally antagonistic. Moreover, global DNA methylation array profiling reveals that AFP+ and AFP- HCC tumors have distinct global DNA methylation patterns and that increased DNA methylation is associated with AFP+ HCC. Interestingly, miR-29 family physiological expression is low in mouse embryonic livers but gradually increases after birth. This is in contrary to AFP expression, which dramatically decreases after birth. Experimentally, we demonstrated that increased AFP expression, or conditioned media from AFP expressing HCC cells, inhibits miR-29a expression in AFP- HCC cells. AFP also inhibited transcription of the miR-29a/b-1 locus and this effect is mediated through c-MYC binding to the miR-29a/b-1 promoter. Our findings indicate that tumor biology differs considerably between AFP+ HCC and AFP- HCC and that AFP is a functional antagonist of miR-29, which may contribute to global epigenetic alterations and poor prognosis in HCC.

ORGANISM(S): Homo sapiens

PROVIDER: GSE52018 | GEO | 2014/09/23

SECONDARY ACCESSION(S): PRJNA227378

REPOSITORIES: GEO

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Project description:The miR-29 family is an important player in the molecular pathophysiology of distinct types of cancer, with roles that seems to depend on cellular context. Reduced miR-29 levels are associated with more aggressive disease and its overexpression in cancer and leukemic cell lines inhibits proliferation. In contrast, its overexpression in hematopoietic progenitors, promotes leukemogenesis. We explored the potential roles of miR-29a in the molecular pathophysiology of T-cell acute lymphoblastic leukemia (T-ALL). As compared to normal T-cells, miR-29a levels are extremely reduced in T-ALL and in the Jurkat cell line. Microarrays analysis in Jurkat cells, following the introduction of synthetic miR-29a mimics, revealed the down-regulation of several predicted targets, including previously described targets (DNMT3a/b, CDK6, PXDN, MCL1, PIK3R1 and CXXC6), and novel targets with roles in active DNA demethylation, such as members of the ten-eleven-translocation (TET) family and TDG. Reduced miR-29a levels contribute to altered epigenetics, as its introduction in Jurkat cells, promotes the demethylation of the AHR gene (commonly methylated in T-ALL). In T-ALL patients, miR-29a levels are significantly associated with blast counts and disease free survival. Our results highlight the relevance of miR-29 in T-ALL physiopathology, and may help to clarify some contrasting findings reported in the literature. In order to identify potential miR-29a targets in T-cell lymphoblastic leukemia, Jurkat cells were electroporated with synthetic RNA molecules corresponding to miR-29a mimics (pre-miR) or inhibitors (anti-miR); and microarray profiles were compared to the profiles of Jurkat cells eletroporated with the corresponding negative controls. Transcripts with levels reduced following the introduction of the pre-miR-29a (as compared to pre-miR-Control), or transcripts acumulated folowing introduction of the anti-miR-29a inhibitor (as compared to anti-miR-Control), were considered potential targets; and were further compared to microRNA target prediction databases. Two paired samples were used for this analysis.

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Modulation of miR-29 Expression by Alpha-fetoprotein is linked to the Hepatocellular Carcinoma Epigenome

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