Since differentiation-induction therapy represents an attractive strategy for treatment of a wide range of malignancies, universal efforts have been devoted to find new and potent differentiation inducers devoid of general toxicities. In that respect, 3-hydrogenkwadaphnin (3-HK), a novel daphnane-type diterpene ester from Dendrostellera lessertii (Thymelaeaceae), was found to be an effective inducer of megakaryocytic differentiation in chronic myelogenous leukemia (CML) K562 cells without any adverse effects on normal cells [Moosavi, M.A., Yazdanparast, R., Sanati, M.H., Nejad, A.S., 2005. 3-Hydrogenkwadaphnin targets inosine 5\\\\\\\'-monophosphate dehydrogenase and triggers post-G1 arrest apoptosis in human leukemia cell lines. International Journal of Biochemistry and Cell Biology 37, 2366-2379]. In this study, we found that inhibition of cellular replication and maturation, induced by the drug, are dependent upon ERK/MAPK activation. Inhibition of MEK activity by PD98059 reversed the growth arrest, decreased adhesive properties, induction of polyploidization and blocked the expression of GPIIb integrin, induced by 3-HK. Immunoblot analyses also showed that 3-HK-induced sustained activation of ERK1/2 from early exposure times, before the onset of differentiation, up to 96 h. Moreover, our results revealed that cyclin D1 and p21(Cip/WAF1) were increased during differentiation. Consequently, it is concluded that up-regulation of cyclin D1, accompanied by the persistent activation of ERK/MAPK, is involved in the megakaryocytic differentiation of K562 cells under the influence of 3-HK.

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