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Investigation of mRNA expression pattern by over-expression of two CEBPB transcription factor isoforms

ABSTRACT: The RNA binding protein Lin28b is highly expressed during embryogenesis but its expression declines in adult tissues, and aberrant expression of Lin28b is associated with tumour development and maintenance. Lin28b regulates the translation of several glycolytic and mitochondrial enzymes in order to enhance cellular metabolism and energy production. Lin28b is repressed by let-7 family microRNAs in a reciprocal negative regulatory circuitry where Lin28b suppresses maturation of let-7. This circuitry obtains input from master regulators such as MYC that transcriptionally upregulates Lin28b, which is required for let-7 suppression and proliferation. Not much is known of how this circuitry is regulated through transcription of the let-7 microRNAs. Here we show that the transcription factor C/EBPbeta-LIP induces aerobic glycolysis and mitochondrial respiration reminiscent to cancer cell metabolism. By integrating transcriptome, proteome and metabolic flux analysis, we reveal that this LIP-induced metabolic reprogramming is dependent on Lin28b and that LIP enhances Lin28b expression through transcriptional repression of the let-7 microRNA family. Transgenic mice overexpressing LIP have reduced levels of let-7 in bone marrow, skin and spleen, which is associated with induction of Lin28b and hyperplasia. This study establishes LIP as a regulator of the let-7/Lin28b regulatory circuitry and we hypothesize that the LIP-controlled let-7/Lin28b regulation is involved in the de-regulation of tissue homeostasis and tumourigenesis.

ORGANISM(S): Mus musculus

PROVIDER: GSE110316 | GEO | 2019/06/26

REPOSITORIES: GEO

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Project description:BACKGROUND & AIMS: C/EBPbeta is involved in numerous process as carcinogenesis but its role is still not clear due to the existence of an active form (LAP) and an inhibitory form (LIP) of this transcription factor. The main goals of the present research were (i) the identification of genes inversely regulated by LAP and LIP i-e the genuine C/EBPbeta molecular signature in the Hep3B human hepatoma cell line (ii) a better understanding of LAP and LIP respective role in hepatic cells survival and proliferation (iii) the search of the C/EBPbeta signature among hepatocellular carcinomas. METHODS: Using Tet-off expression system we engineered Hep3BLAP and Hep3BLIP cells, in which LAP and LIP were over-expressed respectively. Then, using both expression profiling (DNA arrays) and ChIP-on-chip analysis, we identified genes inversely and/or directly regulated by each of the C/EBPbeta isoforms. The expression levels of these genes regulated by LAP/LIP were compared in controls and HCCs patients. RESULTS: We identified 676 genes inversely regulated by LAP and LIP and among these, 45 are direct targets. Using functional studies, we displayed the opposite role of LAP and LIP in staurosporine-induced cell death and the implication of LAP in the repression of Hep3B cells proliferation. Finally we identified a subgroup of HCCs with a deregulation of 165 genes belonging to C/EBPbeta signature and coding for proteins involved in chemoresistance and metastasis formation. CONCLUSIONS: Our study increases knowledge on LAP and LIP functions and provides first evidence that their molecular signature in the HCCs could predict tumor evolution. Total genomic DNA were extracted from 3 Hep3BLAP expressing LAP and were labelled Cy3 fluorochrome. Genomic DNA were extracted from 3 Hep3BLAP expressing LAP, were immunoprecipited with anti-CEBPbeta antibody and were labelled with Cy5 fluorochrome. Each sample was hybridized on an Agilent two-color microarray G4489A (Human Promoter ChIP-on-Chip Set 244K).