Effect of Selective Serotonin (5-HT)2B Receptor Agonist BW723C86 on Epidermal Growth Factor/Transforming Growth Factor-α Receptor Tyrosine Kinase and Ribosomal p70 S6 Kinase Activities in Primary Cultures of Adult Rat Hepatocytes

• Published in: Biological & pharmaceutical bulletin Vol. 42; no. 4; pp. 631 - 637
• Main Authors: Naito, Kota, Kimura, Mitsutoshi, Natsume, Hideshi, Moteki, Hajime, Kurihara, Kazuki, Ogihara, Masahiko
• Format: Journal Article
• Language: English
• Published: Japan The Pharmaceutical Society of Japan 01.04.2019; Japan Science and Technology Agency
• Subjects: Agonists; Animals; Autocrine signalling; Calcium channels (L-type); Calcium permeability; Calcium signalling; Cell Proliferation - drug effects; Cells, Cultured; DNA biosynthesis; Epidermal growth factor; ErbB Receptors - metabolism; Extracellular signal-regulated kinase; Hepatocytes; Hepatocytes - drug effects; Hepatocytes - metabolism; Indoles - pharmacology; Kinases; Male; p70 S6 kinase; Phospholipase C; Phosphorylation; Primary Cell Culture; proliferation (cultured hepatocyte); Protein-tyrosine kinase receptors; Rapamycin; Rats, Wistar; Receptor, Serotonin, 5-HT2B - metabolism; ribosomal p70 S6 kinase (p70S6K); Ribosomal Protein S6 Kinases, 70-kDa - metabolism; Rodents; Secretion; serotonin; Serotonin 5-HT2 Receptor Agonists - pharmacology; Serotonin S2 receptors; Signal transduction; Somatostatin; Thiophenes - pharmacology; TOR protein; Transforming growth factor; transforming growth factor-α; Verapamil; Western blotting; serotonin; transforming growth factor-α; ribosomal p70 S6 kinase (p70S6K); signal transduction; proliferation (cultured hepatocyte)
• ISSN: 0918-6158; 1347-5215; 1347-5215
• DOI: 10.1248/bpb.b18-00831

Serotonin (5-hydroxytryptamine; 5-HT) can induce hepatocyte DNA synthesis and proliferation by autocrine secretion of transforming growth factor (TGF)-α through 5-HT2B receptor/phospholipase C (PLC)/Ca2+ and a signaling pathway involving epidermal growth factor (EGF)/TGF-α receptor tyrosine kinase (RTK)/extracellular signal-regulated kinase 2 (ERK2)/mammalian target of rapamycin (mTOR). In the present study, we investigated whether 5-HT or a selective 5-HT2B receptor agonist BW723C86, would stimulate phosphorylation of TGF-α RTK and ribosomal p70 S6 kinase (p70S6K) in primary cultures of adult rat hepatocytes. Western blotting analysis was used to detect 5-HT- or BW723C86 (10−6 M)-induced phosphorylation of EGF/TGF-α RTK and p70S6K. Our results showed that 5-HT- or BW723C86 (10−6 M)-induced phosphorylation of EGF/TGF-α RTK peaked at between 5 and 10 min. On the other hand, 5-HT- or BW723C86 (10−6 M)-induced phosphorylation of p70S6K peaked at about 30 min. Furthermore, a selective 5-HT2B receptor antagonist LY272015, a specific PLC inhibitor U-73122, a membrane-permeable Ca2+ chelator BAPTA/AM, an L-type Ca2+ channel blocker verapamil, somatostatin, and a specific p70S6K inhibitor LY2584702 completely abolished the phosphorylation of p70S6K induced by both 5-HT and BW723C86. These results indicate that phosphorylation of p70S6K is dependent on the 5-HT2B-receptor-mediated autocrine secretion of TGF-α. In addition, these results demonstrate that the hepatocyte proliferating action of 5-HT and BW723C86 are mediated by phosphorylation of p70S6K, a downstream element of the EGF/TGF-α RTK signaling pathway.