A microRNA-21 surge facilitates rapid cyclin D1 translation and cell cycle progression in mouse liver regeneration
Raymond Ng, … , Niels M. Frandsen, Holger Willenbring
Raymond Ng, … , Niels M. Frandsen, Holger Willenbring
Published February 13, 2012
Citation Information: J Clin Invest. 2012;122(3):1097-1108. https://doi.org/10.1172/JCI46039.
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A microRNA-21 surge facilitates rapid cyclin D1 translation and cell cycle progression in mouse liver regeneration

Abstract

MicroRNA-21 (miR-21) is thought to be an oncomir because it promotes cancer cell proliferation, migration, and survival. miR-21 is also expressed in normal cells, but its physiological role is poorly understood. Recently, it has been found that miR-21 expression is rapidly induced in rodent hepatocytes during liver regeneration after two-thirds partial hepatectomy (2/3 PH). Here, we investigated the function of miR-21 in regenerating mouse hepatocytes by inhibiting it with an antisense oligonucleotide. To maintain normal hepatocyte viability and function, we antagonized the miR-21 surge induced by 2/3 PH while preserving baseline expression. We found that knockdown of miR-21 impaired progression of hepatocytes into S phase of the cell cycle, mainly through a decrease in levels of cyclin D1 protein, but not Ccnd1 mRNA. Mechanistically, we discovered that increased miR-21 expression facilitated cyclin D1 translation in the early phase of liver regeneration by relieving Akt1/mTOR complex 1 signaling (and thus eIF-4F–mediated translation initiation) from suppression by Rhob. Our findings reveal that miR-21 enables rapid hepatocyte proliferation during liver regeneration by accelerating cyclin D1 translation.

Authors

Raymond Ng, Guisheng Song, Garrett R. Roll, Niels M. Frandsen, Holger Willenbring

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Figure 3

miR-21 regulates cyclin D1 translation.

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miR-21 regulates cyclin D1 translation. (A) Transfection of 40 nM miR-21...
(A) Transfection of 40 nM miR-21–ASO decreased cyclin D1 levels in Hepa1,6 cells approximately 2-fold. (B) Transfection of 40 nM miR-21 mimic increased cyclin D1 levels in Hepa1,6 cells approximately 2-fold. Results are representative of 3 separate experiments. (C) Elution profile of fractionated cytoplasmic lysates from Hepa1,6 cells transfected with miR-21–ASO or nontargeting ASO (Control). Untranslated fractions, containing 40S or 60S ribosomal subunits, were eluted first, followed by monosomal fractions containing 80S single intact ribosomes and polysomal fractions containing multiple associated ribosomes. Absorbance readings at 254 nm were automatically converted into potential values, which were plotted against the eluted fractions. (D) qRT-PCR showed that Ccnd1 mRNA levels in RNA isolated from the actively translated polysomal fractions were lower in miR-21–ASO–transfected cells than in control cells. Relative levels of Ccnd1 mRNA in fractions were determined by normalization to Gapdh. These values were further normalized to Ccnd1 mRNA levels in unfractionated samples to account for potential differences in starting cell numbers. Data represent mean ± SEM. *P < 0.05.