S6 kinase 1 is required for rapamycin-sensitive liver proliferation after mouse hepatectomy
Catherine Espeillac, Claudia Mitchell, Séverine Celton-Morizur, Céline Chauvin, Vonda Koka, Cynthia Gillet, Jeffrey H. Albrecht, Chantal Desdouets, Mario Pende
Catherine Espeillac, Claudia Mitchell, Séverine Celton-Morizur, Céline Chauvin, Vonda Koka, Cynthia Gillet, Jeffrey H. Albrecht, Chantal Desdouets, Mario Pende
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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 4

Expression of S6K1 in liver rescues the proliferation defect.

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Expression of S6K1 in liver rescues the proliferation defect. (A) Immuno...
(A) Immunoblot analysis of protein extracts from liver, spleen, kidney, and lung of the WT genotype using anti-S6K1 and anti-tubulin antibodies. Mice were treated or not with adenovirus S6K1 1 week before PH and sacrificed 42 hours after PH. S6K1 tot, S6K1 total. (B) BrdU-positive hepatocytes of the indicated genotypes were treated with adenovirus expressing GFP or S6K1 1 week before PH and sacrificed 42 hours after PH. Data are expressed as the percentage of BrdU-positive cells ± SEM for at least 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 mice treated with GFP adenovirus. (C) BrdU-positive cultured hepatocytes of the indicated genotype at different times after plating. Data are expressed as the percentage of BrdU-positive cells ± SEM for duplicate plates per genotype. A representative experiment is shown. Data were reproduced in 3 independent cultures.