The differentiation of K562 chronic myelogenous leukemia (CML) cells by smenospongine, which is a sesquiterpene aminoquinone isolated from a marine sponge, was examined. Smenospongine increased hemoglobin production in K562 cells at concentrations of 3–15 μM. In addition, flow cytometric analysis of smenospongine-treated K562 cells with FITC-labeled glycophorin A antibody showed an increase of glycophorin A expression, a marker for erythroid differentiation. Cell-cycle analysis showed G1 arrest in K562 cells after treatment with smenospongine for 24 h. The effect on expression of CIP/KIP family cyclin-dependent kinase inhibitors was investigated by Western blotting analysis and the result showed increased expression of p21, which is known to play an important role in differentiation. Furthermore, smenospongine was also found to inhibit the phosphorylation of Crkl, a substrate of Bcr–Abl tyrosine kinase, which is known as a causative protein of CML. In conclusion, our investigation indicated that smenospongine induced the differentiation of K562 cells into erythroblasts along with cell-cycle arrest at G1 phase and the mechanism might be attributed to the increased expression of p21.
aGraduate School of Pharmaceutical Sciences, Osaka University, Osaka, Japan
Sponsorship: This study was supported by The Takeda Science Foundation, The Houansha Foundation, The Tokyo Biochemical Research Foundation, The Uehara Memorial Foundation, and The Ministry of Education, Culture, Sports, Science and Technology of Japan.
Correspondence to M. Kobayashi, Graduate School of Pharmaceutical Sciences, Osaka University, Yamada-oka 1-6, Suita, Osaka 565-0871, Japan
Tel: +81 6 6879-8215; fax: +81 6 6879-8219;
Received 30 September 2003 Revised form accepted 6 January 2004