Signal transduction pathway for l-ascorbic acid- and l-ascorbic acid 2-glucoside-induced DNA synthesis and cell proliferation in primary cultures of adult rat hepatocytes

摘要

We examined the effects of L-ascorbic acid and its analogues onDNA synthesis and cell proliferation. We also investigated the signaltransduction pathways involved in the induction of mitogenesis byL-ascorbic acid and its analogues using primary cultures of adult rathepatocytes. Following a 4-h serum-free cultivation, both L-ascorbic acidand its stable analogue, L-ascorbic acid 2-glucoside, time- anddose-dependently stimulated hepatocyte DNA synthesis and cellproliferation, with EC50 values of 6.46 ? 10-8 M and 3.34 ? 10-8 M,respectively. Dehydroascorbic acid (10-6 M - 10-5 M) weakly stimulatedhepatocyte mitogenesis, whereas isoascorbic acid (10-9 M ? 10-5 M) had noeffect. Hepatocyte mitogenesis induced by L-ascorbic acid or L-ascorbic acid2-glucoside was dose-dependently abolished by treatment with monoclonalantibodies against insulin-like growth factor (IGF)-I receptor, but not bytreatment with monoclonal antibodies against insulin receptor or IGF-IIreceptor. Western blot analysis showed that both L-ascorbic acid andL-ascorbic acid 2-glucoside significantly stimulated IFG-I receptor tyrosinekinase activity within 3 min, and mitogen-activated protein (MAP) kinaseactivity within 5 min. These results demonstrate that both L-ascorbic acidand L-ascorbic acid 2-glucoside induce DNA synthesis and cell proliferationin primary cultures of adult rat hepatocytes by interacting with the IGF-Ireceptor site and by activating the receptor tyrosine kinase/MAP kinasepathway.