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Cancer Lett. 2008 Jun 18;264(2):316-25. doi: 10.1016/j.canlet.2008.02.011. Epub 2008 Mar 14.

Bcl-2 overexpression attenuates SP600125-induced apoptosis in human leukemia U937 cells.

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  • 1Faculty of Applied Marine Science, Cheju National University, Jeju Special Self-Governing Province 690-756, South Korea.


SP600125 is a specific inhibitor of c-Jun N-terminal kinase (JNK) that is known to strongly induce apoptosis and block cell cycle progression in G2/M phase. In this study, we demonstrated that treatment of U937 cells with SP600125 resulted in significant G2/M cell cycle arrest that was due to decreased cyclin B1 and cdc25c protein levels. Moreover, SP600125 promoted LDH release and DNA fragmentation that was associated with caspase-3 activation and degradation of its substrates. In contrast, overexpression of the antiapoptotic protein Bcl-2 rendered leukemia cells resistant to SP600125-induced apoptosis, but more sensitive to G2/M phase arrest and endoreduplication (>4N DNA). Overexpression of Bcl-2 significantly inhibited SP600125-induced caspase-3 activation and degradation of its substrates, and sustained expression levels of the IAP-2 proteins following SP600125 treatment. The inhibitory effect of Bcl-2 on apoptosis was attenuated by treatment with the small molecule Bcl-2 inhibitor, HA14-1. These data provide important mechanistic insights related to Bcl-2-mediated resistance to SP600125-induced apoptosis, and induction of G2/M phase arrest and endoreduplication.

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