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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Research Article Hepatology

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 4

Inhibition of miR-21 delays S phase entry of hepatocytes after 2/3 PH.

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Inhibition of miR-21 delays S phase entry of hepatocytes after 2/3 PH. (...
(A and B) Quantification of Ki67 and PCNA immunostainings (both brown) showed that many hepatocytes had entered S phase at 36 hours after 2/3 PH in control mice. Significantly fewer hepatocytes stained positive for these markers or cyclin D1 (all brown) in mice injected with miR-21–ASO. For each immunostaining, approximately 1,500 hepatocytes (250 per frame) were analyzed per time point and treatment. Original magnification, ×200. (C) Immunoblotting showed lower cyclin D1 protein levels at 36 hours after 2/3 PH in livers of mice injected with miR-21–ASO compared with controls. Numbers indicate protein levels relative to time point 0 hours after 2/3 PH. Gapdh was analyzed as a loading control. (D) qRT-PCR showed that miR-21–ASO injection did not interfere with induction of liver Ccnd1 transcription at 36 hours after 2/3 PH. At least 3 mice were analyzed for each time point and treatment. miR-21–ASO was injected at 6 hours after 2/3 PH. Control mice were injected with carrier at 6 hours after 2/3 PH. Data represent mean ± SEM. *P < 0.05, **P < 0.01.