S6 kinase 1 is required for rapamycin-sensitive liver proliferation after mouse hepatectomy
Catherine Espeillac, … , Chantal Desdouets, Mario Pende
Catherine Espeillac, … , Chantal Desdouets, Mario Pende
Published June 1, 2011
Citation Information: J Clin Invest. 2011;121(7):2821-2832. https://doi.org/10.1172/JCI44203.
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Research Article Hepatology

S6 kinase 1 is required for rapamycin-sensitive liver proliferation after mouse hepatectomy

Abstract

Rapamycin is an antibiotic inhibiting eukaryotic cell growth and proliferation by acting on target of rapamycin (TOR) kinase. Mammalian TOR (mTOR) is thought to work through 2 independent complexes to regulate cell size and cell replication, and these 2 complexes show differential sensitivity to rapamycin. Here we combine functional genetics and pharmacological treatments to analyze rapamycin-sensitive mTOR substrates that are involved in cell proliferation and tissue regeneration after partial hepatectomy in mice. After hepatectomy, hepatocytes proliferated rapidly, correlating with increased S6 kinase phosphorylation, while treatment with rapamycin derivatives impaired regeneration and blocked S6 kinase activation. In addition, genetic deletion of S6 kinase 1 (S6K1) caused a delay in S phase entry in hepatocytes after hepatectomy. The proliferative defect of S6K1-deficient hepatocytes was cell autonomous, as it was also observed in primary cultures and hepatic overexpression of S6K1-rescued proliferation. We found that S6K1 controlled steady-state levels of cyclin D1 (Ccnd1) mRNA in liver, and cyclin D1 expression was required to promote hepatocyte cell cycle. Notably, in vivo overexpression of cyclin D1 was sufficient to restore the proliferative capacity of S6K-null livers. The identification of an S6K1-dependent mechanism participating in cell proliferation in vivo may be relevant for cancer cells displaying high mTOR complex 1 activity and cyclin D1 accumulation.

Authors

Catherine Espeillac, Claudia Mitchell, Séverine Celton-Morizur, Céline Chauvin, Vonda Koka, Cynthia Gillet, Jeffrey H. Albrecht, Chantal Desdouets, Mario Pende

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Figure 1

mTORC1 regulation of liver regeneration after partial hepatectomy.

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mTORC1 regulation of liver regeneration after partial hepatectomy. (A) B...
(A) BrdU-positive hepatocytes of the indicated genotypes. Mice were injected intraperitoneally with 5 mg/kg of the rapamycin derivate temsirolimus or with placebo 2 hours before PH and then daily until sacrifice (42 hours after PH). Data are expressed as the percentage of BrdU-positive cells ± SEM for 4 mice per genotype. Representative images of BrdU and β-catenin coimmunostaining are shown. Scale bar: 50 μm. *P < 0.05 versus WT mice; #P < 0.05 versus placebo mice. (B and C) Immunoblot analysis of protein extracts from liver of the indicated genotype from sham-operated mice (sham) or at different times after PH. When indicated, mice were injected intraperitoneally with 5 mg/kg of the rapamycin derivate temsirolimus or with placebo 2 hours before PH and then daily until sacrifice (24 hours after PH). Proteins were revealed using the indicated antibodies. P-S6K 389, phosphorylated S6K1 (Thr 389); P-S6 235-236, phosphorylated rpS6 (Ser 235/236); P-S6 240-244, phosphorylated rpS6 (Ser 240/244); P-4EBP 65, phosphorylated 4EBP (Ser 65); P-Akt 473, phosphorylated Akt (Ser 473); P-PRAS40 246, phosphorylated PRAS40 (Thr 246); P-GSK3b 9, phosphorylated GSK3β (Ser 9).