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 5

miR-21 induction in liver regeneration decreases Rhob expression by direct targeting.

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miR-21 induction in liver regeneration decreases Rhob expression by dire...
(A and B) Inverse correlation of miR-21 and Rhob expression levels after 2/3 PH. miR-21 induction after 2/3 PH was associated with decreased Rhob mRNA (A) and Rhob protein (B) levels. Numbers indicate protein level relative to time point 0 hours after 2/3 PH. Gapdh was analyzed as a loading control. (C) High prediction score and favorable binding energy suggested that miR-21 targets the 3′ UTR of Rhob. The complementary sequence in the Rhob 3′ UTR and the seed region of miR-21 (red letters) is conserved among mammalian species. (D) Liver Rhob mRNA levels increased 6 hours after miR-21–ASO injection. Control mice were injected with carrier. At least 3 mice were analyzed per time point and treatment. (E–H) Direct inhibition of Rhob by miR-21. (E) Transfection of miR-21 mimic into Hepa1,6 cells decreased Rhob mRNA. (F) The activity of a luciferase reporter gene linked to the Rhob 3′ UTR was inhibited by miR-21 mimic in a dose-dependent fashion. Mutation of the Rhob 3′ UTR sequence complimentary to the miR-21 seed sequence prevented inhibition by miR-21 mimic. (G) Transfection of miR-21 inhibitor into Hepa1,6 cells increased Rhob mRNA. (H) miR-21 inhibitor effectively restored the activity of a luciferase reporter gene linked to the Rhob 3′ UTR in Hepa1,6 cells transfected with miR-21 mimic. Mutation of the Rhob 3′ UTR sequence complimentary to the miR-21 seed sequence prevented this effect. Data represent mean ± SEM. *P < 0.05.