A microRNA-21 surge facilitates rapid cyclin D1 translation and cell cycle progression in mouse liver regeneration
Raymond Ng, Guisheng Song, Garrett R. Roll, Niels M. Frandsen, Holger Willenbring
Raymond Ng, Guisheng Song, Garrett R. Roll, Niels M. Frandsen, Holger Willenbring
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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.