Abstract
We investigated the effects of transforming growth factor α (TGF-α) on DNA synthesis and proliferation in primary cultures of adult rat hepatocytes and examined the influence of α and β adrenoceptor agonists on the TGF-α-induced responses. TGF-α (1.0 ng/ml) produced a 4.1-fold elevation of DNA synthesis during 3 h of culture and a 1.2-fold increase in the nucleus number (proliferation) during 4 h of culture at a cell density of 3.3 × 104 cells/cm2. The TGF-α-induced hepatocyte DNA synthesis and proliferation were dose-dependent at EC50 values of 0.36 ng/ml and 0.45 ng/ml, respectively. Hepatocyte DNA synthesis and proliferation induced by 1.0 ng/ml TGF-α did not reduce even at higher initial plating densities (5.0 × 104 and 1.0 × 105 cells/cm2). Increasing concentrations of the β2 adrenoceptor agonist metaproterenol (10−7–10−6 M) markedly reduced the proliferative effects of TGF-α, whereas those of the α2 adrenoceptor agonist 5-bromo-6-[2-imidazolin-2-yl-amino]-quinoxaline (UK-14304; 10−6–10−5 M) and the α1adrenoceptor agonist phenylephrine (10−7–10−6 M) significantly potentiated the TGF-α action. The proliferative effects of TGF-α (1.0 ng/ml) were not affected significantly by a monoclonal antiepidermal growth factor receptor antibody (1–100 ng/ml) and were almost completely blocked by specific inhibitors of signal transducers such as genistein (10−5 M), 1–6[[17β-3methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrol2,5-dione (U-73122; 0−5 M), wortmannin (5 × 10−7M), sphingosine (5 × 10−6 M), 2′-amino-3′-methoxyflavone (PD98059; 5 × 10−5 M), and rapamycin (10 ng/ml). These results suggest that among the elements that link signals of cell surface receptor to the nucleus, the proliferative action of TGF-α is mediated, at least, by tyrosine kinase, phospholipase C, phosphatidylinositol 3-kinase, protein kinase C, mitogen-activated protein kinase kinase, and ribosomal protein p70 S6 kinase.
Footnotes
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Send reprint requests to: Masahiko Ogihara, 1-1, Keyakidai, Sakado City, Saitama 350-0290, Japan. E-mail:ogiharam{at}josai.ac.jp
- Abbreviations:
- EGF
- epidermal growth factor
- HGF
- hepatocyte growth factor
- PDGF
- platelet-derived growth factor
- TGF-α
- transforming growth factor-α
- PI3K
- phosphatidylinositol 3′ kinase
- MAP
- mitogen-activated protein
- PMA
- phorbol 12-myristate 13-acetate
- 8-br-cAMP
- 8-bromo cAMP
- Received February 11, 1999.
- Accepted June 14, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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