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

Abstract

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-d inhibits proliferation of DU145 human prostate cancer cells by inducing apoptosis and arresting the cell cycle at G0/G1 phase

“…A previous study showed that SS induced apoptosis via mitochondria-dependent and -independent pathways (11). As involvement of a mitochondria-mediated pathway in apoptosis is of notable value in the treatment of cancer (29), the effect of SSd on the mitochondrial apoptotic pathway was investigated in the present study.…”

“…Previous studies have reported that SSd inhibited proliferation of several cancer cell lines (8)(9)(10)(11), while its effect on human prostate cancer cells remained under investigation. The present study revealed, for the first time to the best of our knowledge, that SSd induced apoptosis in the DU145 human prostate cancer cell line.…”

“…Thus far, at least 10 types of SS have been identified, and among which saikosaponin-d (SSd) is considered to be the most active component (1,7). Studies have reported that SS may potently inhibit the proliferation of hepatocellular carcinoma (8), cervical cancer (9), lung adenocarcinoma (10), colon carcinoma (11), breast cancer (12) and melanoma (13) cells. However, the effect of SS on human prostate cancer cell lines remains to be elucidated.…”

Jolkinolide B from Euphorbia fischeriana Steud Induces Apoptosis in Human Leukemic U937 Cells through PI3K/Akt and XIAP Pathways

“…Apoptosis is an important defense mechanism that plays a key role in cancer prevention and treatment (Kim and Hong, 2011). Apoptosis signaling is regulated by various pro-and antiapoptotic proteins (Ahn et al, 2010).…”

Metabolism of Saikosaponin a in Rats: Diverse Oxidations on the Aglycone Moiety in Liver and Intestine in Addition to Hydrolysis of Glycosidic Bonds

“…Saikosaponins, the major bioactive ingredients of the genus Bupleurum with a long history of medicinal use, exert significant pharmacological activities, including antitumor (targeting various cancer cells) (Motoo and Sawabu, 1994;Ahn et al, 1998;Hsu et al, 2000;Tsai et al, 2002;Wen-Sheng, 2003;Hsu et al, 2004;Kim and Hong, 2011), chemosensitizing (Wang et al, 2010a), anti-inflammatory (Yokoyama et al, 1981;Nose et al, 1989a;Bermejo Benito et al, 1998), immunomodulatory (Kumazawa et al, 1989;Leung et al, 2005;Sun et al, 2009), hepatoprotective (Abe et al, 1980;Fan et al, 2007;Wu et al, 2008), antinephritic Chen et al, 2008;Hattori et al, 2008), antibacterial and antiviral (Kumazawa et al, 1990;Chiang et al, 2003;Cheng et al, 2006), estrogenic (Wang et al, 2010b), and promoting amylase secretion in rat pancreatic acini (Yu et al, 2002). On the other hand, saikosaponins have also been reported to be responsible for toxicity induced by their hemolytic action (Abe et al, 1978a, b;Nose et al, 1989b).…”