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Biochem Soc Trans October 1, 2009; 37 (Pt 5): 931-5.

miRNPs: versatile regulators of gene expression in vertebrate cells.

Steitz JA , Vasudevan S .

TNFalpha (tumour necrosis factor alpha) mRNA bears in its 3''-UTR (untranslated region) a conserved ARE (AU-rich element), a signal that exerts tight post-transcriptional control over the expression of TNFalpha and other cytokines. We found that the TNFalpha ARE increases translational efficiency when cell growth is arrested, a physiologically relevant state occurring during inflammation, angiogenesis and monocyte differentiation. Under these conditions, called quiescence, the miRNP (microribonucleoprotein)-associated proteins FXR1 (Fragile X mental retardation-related protein 1) and AGO2 (Argonaute 2), which are usually considered negative regulators, are transformed into effector molecules that bind the ARE to activate translation. We then identified a specific miRNA (microRNA) that directs the association of AGO2 and FXR1 with the ARE during translational up-regulation. Two other well-characterized miRNAs likewise promote translation activation in quiescent or in contact-inhibited cells; yet, they repress translation in proliferating cells in the late S/G(2)-phase. We conclude that translational regulation by miRNPs oscillates between repression and activation as a function of the cell cycle. The activating role of miRNAs is now being confirmed in the immature Xenopus oocyte, which mimics the quiescent state.

PubMed ID: 19754429
Article link: Biochem Soc Trans
Grant support: P01 CA016038 NCI NIH HHS , R01 GM026154 NIGMS NIH HHS

Genes referenced: ago2 fxr1

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