, Volume 16, Issue 2, pp 184–197 | Cite as

Sequential caspase-2 and caspase-8 activation is essential for saikosaponin a-induced apoptosis of human colon carcinoma cell lines

  • Byeong Mo Kim
  • Sung Hee Hong
Original Paper


In this study, we investigated the signaling pathways implicated in SSa-induced apoptosis of human colon carcinoma (HCC) cell lines. SSa-induced apoptosis of HCC cells was associated with proteolytic activation of caspase-9, caspase-3, and PARP cleavages and decreased levels of IAP family members, such as XIAP and c-IAP-2, but not of survivin. The fluorescence intensity of DiOC6 was significantly reduced after SSa treatment. CsA significantly inhibited SSa-induced loss of mitochondrial transmembrane potential and moderately inhibited SSa-induced cell death. SSa treatment also enhanced the activities of caspase-2 and caspase-8, Bid cleavage, and the conformational activation of Bax. Additionally, SSa-induced apoptosis was inhibited by both the selective caspase-2 inhibitor z-VDVAD-fmk and the selective caspase-8 inhibitor z-IETD-fmk and also by si-RNAs against caspase-2 and caspase-8. The selective caspase-9 inhibitor, z-LEHD-fmk, also inhibited SSa-induced apoptosis, albeit to a lesser extent compared to z-VDVAD-fmk and z-IETD-fmk, indicating that both mitochondria-dependent and mitochondria-independent pathways are associated with SSa-induced apoptosis. Both z-VDVAD-fmk and z-IETD-fmk significantly attenuated the colony-inhibiting effect of SSa. Moreover, inhibition of caspase-2 activation by the pharmacological inhibitor z-VDVAD-fmk, or by knockdown of protein levels using a si-RNA, suppressed SSa-induced caspase-8 activation, Bid cleavage, and the conformational activation of Bax. Although caspase-8 is an initiator caspase like caspase-2, the inhibition of caspase-8 activation by knockdown using a si-RNA did not suppress SSa-induced caspase-2 activation. Altogether, our results suggest that sequential activation of caspase-2 and caspase-8 is a critical step in SSa-induced apoptosis.


Saikosaponin a (SSa) Human colon carcinoma (HCC) Apoptosis Caspase-2 Caspase-8 Cell death mechanisms 



Saikosaponin a


Human colon carcinoma










Propidium iodide


Fluorescence-activated cell sorter






Mitochondrial membrane potential


Cyclosporine A


Mitochondrial permeability transition


Inhibitors of apoptosis proteins


Analysis of variance



This work was supported by the National Nuclear R&D Program of the Ministry of Education, Science and Technology (MEST) of the Republic of Korea.


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Copyright information

© Springer Science+Business Media, LLC 2010

Authors and Affiliations

  1. 1.Division of Radiation Cancer ResearchKorea Institute of Radiological and Medical SciencesSeoulKorea

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