Fig. 4. The mTOR pathway is activated upon Hgf stimulation and is required for Met-triggered Mdm2 translation in embryonic hepatocytes. (A) Hgf activates mTOR-p70^s6k signaling. p70^s6k is phosphorylated on T₃₈₉ upon Hgf stimulation. Because this phosphorylation is abolished in the presence of LY 294002 (5 µM) or rapamycin (rapa: 1 µM), it must require intact PI3K and mTOR signaling. (B) Hgf stimulation induces phosphorylation of the following mTOR downstream signals: p70^s6k on residues T₄₂₁/S₄₂₄, S6 ribosomal protein on S_235/236 and 4EBP1 on S₆₅. (C) Rapamycin prevents the upregulation of Mdm2 by Hgf in embryonic hepatocyte cultures. (D) Newly synthesized Mdm2 and p53 proteins were analyzed by the immunoprecipitation of ³⁵S-methionine/cysteine-labeled protein extracts from embryonic hepatocytes treated or not with Hgf and/or rapamycin. Rapamycin inhibits the translation of Mdm2, but not of p53. The bottom panels show levels of Mdm2 on total lysates.