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Abstract
Promoter of the Drosophila proliferating cell nuclear antigen (PCNA) gene contains DRE (Drosophila DNA replication‐related element) required for the high level expression of replication‐related genes. Recently, we found that promoter region of the D‐raf (a Drosophila homolog of the human c‐raf‐1) contains two sequences homologous to the ORE and demonstrated the DRE/DREF (DRE‐binding factor) involvement in regulation of the D‐raf gene. In this study, using ursolic acid (UA), a pentacyclic triterpene acid reported to possess antitumor activities, we examined effects of UA on proliferation of the Drosophila cultured Kc cells and on expression of the PCNA and D‐raf genes. UA showed an inhibitory effect on proliferation of the Kc cells in a concentration‐dependent manner in DNA content assays and [3H]thymidine incorporation assays. The IC50 value of anti‐proliferative effects of UA in DNA content assays was about 7.5 μM. UA showed inhibitory effects on expression of the PCNA as well as on that of the D‐raf, which were examined with the reporter plasmid p5'‐168DPCNACAT or p5'‐878DrafCAT, respectively. The results obtained in the present study suggest that expression of the PCNA and D‐raf genes is coordinately regulated in at least UA‐treated Kc cells and that down‐regulation of expression of the PCNA and D‐raf genes might be related with the anti‐tumor activities of UA.
Notes
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