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  • HEMATOPOIETIC STEM-CELLS  (1)
  • IDENTIFICATION  (1)
  • 1
    Keywords: DIFFERENTIATION ; HEMATOPOIETIC STEM-CELLS ; INTESTINAL CRYPTS ; LYMPHOCYTE DEVELOPMENT
    Abstract: Previous studies have established pivotal roles for c-Myc and its homolog N-Myc in hematopoietic stem cell (HSC) maintenance and niche-dependent differentiation. However, it remains largely unclear how c-Myc expression is regulated in this context. Here, we show that HSCs and more committed progenitors express similar levels of c-myc transcripts. Using knock-in mice expressing a functional enhanced green fluorescent protein-c-Myc fusion protein under control of the endogenous c-myc locus, c-Myc protein levels were assessed. Although HSCs express low levels of c-Myc protein, its expression increases steadily during progenitor differentiation. Thus, mRNA and protein expression patterns differ significantly in stem/progenitor cells, suggesting that c-Myc expression is largely controlled posttranscriptionally. Moreover, interferon-alpha exposure, which activates dormant HSCs, strongly induces c-Myc expression at the protein level but not at the transcript level. This posttranscriptional mechanism of c-Myc regulation provides the blood system with a rapid way to adjust c-Myc expression according to demand during hematopoietic stress.
    Type of Publication: Journal article published
    PubMed ID: 24795346
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  • 2
    Keywords: LUNG-CANCER ; HEPATOCELLULAR-CARCINOMA ; GENE-EXPRESSION ; GENOME ; IDENTIFICATION ; C-MYC ; POOR-PROGNOSIS ; INCREASED EXPRESSION ; CODING REGION ; CRD-BP
    Abstract: Selected long non-coding RNAs (lncRNAs) have been shown to play important roles in carcinogenesis. Although the cellular functions of these transcripts can be diverse, many lncRNAs regulate gene expression. In contrast, factors that control the expression of lncRNAs remain largely unknown. Here, we investigated the impact of RNA binding proteins on the expression of the liver cancer-associated lncRNA HULC (Highly Up-regulated in Liver Cancer). First, we validated the strong up-regulation of HULC in human hepatocellular carcinoma. To elucidate post-transcriptional regulatory mechanisms governing HULC expression, we applied an RNA affinity purification approach to identify specific protein interaction partners and potential regulators. This method identified the family of IGF2BPs (IGF2 mRNA-binding proteins) as specific binding partners of HULC. Depletion of IGF2BP1, also known as IMP1, but not of IGF2BP2 or -3, led to an increased HULC half-life and higher steady-state expression levels, indicating a post-transcriptional regulatory mechanism. Importantly, HULC represents the first IGF2BP substrate that is destabilized. To elucidate the mechanism by which IGF2BP1 destabilizes HULC, the CNOT1 protein was identified as a novel interaction partner of IGF2BP1. CNOT1 is the scaffold of the human CCR4-NOT deadenylase complex, a major component of the cytoplasmic RNA decay machinery. Indeed, depletion of CNOT1 increased HULC half-life and expression. Thus, IGF2BP1 acts as an adaptor protein that recruits the CCR4-NOT complex and thereby initiates the degradation of the lncRNA HULC. Conclusion: Our findings provide important insights into the regulation of lncRNA expression and identify a novel function for IGF2BP1 in RNA metabolism.
    Type of Publication: Journal article published
    PubMed ID: 23728852
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