Signal Transduction Mechanism for Serotonin 5-HT2B Receptor-Mediated DNA Synthesis and Proliferation in Primary Cultures of Adult Rat Hepatocytes

摘要

The involvement of serotonin (5-hydroxytryptamine; 5-HT) and the 5-HT2 receptor subtypes in theinduction of DNA synthesis and proliferation was investigated in primary cultures of adult rat hepatocytesto elucidate the intracellular signal transduction mechanisms. Hepatocyte parenchymal cells maintainedin a serum-free, defined medium, synthesized DNA and proliferated in the presence of 5-HT or a selective5-HT2B receptor agonist, BW723C86, but not in the presence of 5-HT2A, or 5-HT2C receptor agonists (TCB-2and CP809101, respectively), in a time- and dose-dependent manner. A selective 5-HT2B receptor antagonist,LY272015 (10 7 M), and a specific phospholipase C (PLC) inhibitor, U-73122 (10 6 M), as well as specific inhibitorsof growth-related signal transducers?including AG1478, LY294002, PD98059, and rapamycin?completelyinhibited 5-HT (10 6 M)- or BW723C86 (10 6 M)-induced hepatocyte DNA synthesis and proliferation.Both 5-HT and BW723C86 were shown to significantly stimulate the phosphorylation of epidermal growthfactor (EGF)/transforming growth factor (TGF)-α receptor tyrosine kinase (p175 kDa) and extracellularsignal-regulated kinase (ERK) 2 on Western blot analysis. These results suggest that the proliferative mechanismof activating 5-HT is mediated mainly through 5-HT2B receptor-stimulated Gq/PLC and EGF/TGF-α-receptor/phosphatidylinositol 3-kinase (PI3K)/ERK2/mammalian target of rapamycin (mTOR) signalingpathways in primary cultured hepatocytes.