Effects of branched-chain amino acids on DNA synthesis and proliferation in primary cultures of adult rat hepatocytes.
We investigated the effects of branched-chain amino acids on DNA synthesis and proliferation in primary cultures of adult rat hepatocytes. Of the branched-chain amino acids, only leucine (10(-5)-10(-3) M) induced hepatocyte DNA synthesis and proliferation in a time- and dose-dependent manner. The addition of valine or isoleucine on its own had no significant effects on the hepatocyte DNA synthesis and proliferation. When combined, isoleucine competitively antagonized leucine-stimulated hepatocyte mitogenesis. U73122 (10(-6) M), AG1478 (10(-7) M), wortmannin (10(-7) M), PD98059 (10(-6) M) and rapamycin (10 ng/ml) inhibited the ability of leucine to stimulate the hepatocyte DNA synthesis and proliferation, suggesting that phospholipase C, tyrosine kinase, phosphatidylinositol 3-kinase, mitogen-activated protein (MAP) kinase, and p70 S6 kinase are involved in leucine signaling. The mitogenic effects of leucine are completely abolished by the addition of anti-transforming growth factor-alpha (TGF-alpha) antibody to the culture medium. Furthermore, leucine stimulated TGF-alpha secretion into the culture medium and the leucine effect was inhibited by U73122. Isoleucine alone had no significant effect on TGF-alpha secretion but this agent blocked leucine-induced TGF-alpha secretion. The results suggest that leucine triggers TGF-alpha secretion through a putative leucine receptor. The secreted TGF-alpha then stimulates hepatocyte DNA synthesis and proliferation through activation of TGF-alpha receptor to induce tyrosine kinase/MAP kinase activity and other downstream growth-related signal transducers.
Kimura
Mitsutoshi
M
Department of Clinical Pharmacology, Faculty of Pharmaceutical Sciences, Josai University, 1-1, Keyakidai, Sakado City, Saitama 350-0295, Japan.
Ogihara
Masahiko
M
D000597:Amino Acids, Branched-Chain / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D049109:Cell Proliferation / Q000187:drug effects*; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D007532:Isoleucine / Q000008:administration & dosage / Q000494:pharmacology; D007930:Leucine / Q000008:administration & dosage / Q000494:pharmacology; D020935:MAP Kinase Signaling System / Q000187:drug effects; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D008954:Models, Biological; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D051381:Rats; D017526:Receptor, IGF Type 1 / Q000037:antagonists & inhibitors; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000037:antagonists & inhibitors; D015398:Signal Transduction / Q000187:drug effects; D016211:Transforming Growth Factor alpha / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors; D014633:Valine / Q000008:administration & dosage / Q000494:pharmacology
D000597:Amino Acids, Branched-Chain; D000911:Antibodies, Monoclonal; D004791:Enzyme Inhibitors; D005419:Flavonoids; D000081082:Phosphoinositide-3 Kinase Inhibitors; D016211:Transforming Growth Factor alpha; D007532:Isoleucine; D004247:DNA; D011505:Protein-Tyrosine Kinases; D017526:Receptor, IGF Type 1; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D019950:Mitogen-Activated Protein Kinase 1; D010738:Type C Phospholipases; D007930:Leucine; D014633:Valine; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one