Kang, Su JinLee, Young JoonKang, Sung GuCho, SoyoungYoon, WonsuckLim, Ji HongMin, Sang-HyunLee, Tae HoKim, Byeong Mo2018-01-182017Kang, Su Jin, Young Joon Lee, Sung Gu Kang, Soyoung Cho, Wonsuck Yoon, Ji Hong Lim, Sang-Hyun Min, Tae Ho Lee, and Byeong Mo Kim. 2017. “Caspase-4 is essential for saikosaponin a-induced apoptosis acting upstream of caspase-2 and γ-H2AX in colon cancer cells.” Oncotarget 8 (59): 100433-100448. doi:10.18632/oncotarget.22247. http://dx.doi.org/10.18632/oncotarget.22247.http://nrs.harvard.edu/urn-3:HUL.InstRepos:34651776Saikosaponin a (SSa), a bioactive phytochemical from Bupleurum, triggers sequential caspase-2 and caspase-8 activation, and thereby induces caspase-mediated apoptosis in human colon carcinoma (HCC) cells. However, the upstream mechanism of caspase-2 activation remains unknown. Therefore, we investigated the signaling mechanisms underlying SSa-induced caspase activation and apoptosis in HCC cells. SSa treatment triggered marked antitumor effects, especially in HCC cells, in a cell culture model and a mouse xenograft model. SSa also induced the activation of several endoplasmic reticulum (ER) stress signals. Specifically, caspase-4, a critical regulator of ER stress-induced apoptosis, was activated significantly after SSa treatment. Mechanistically, selective inhibition of caspase-4 suppressed SSa-induced apoptosis, colony inhibition, and the activation of caspase-3, -8, and -2, but not vice versa. Consistent with the important role of caspase-2 in the DNA damage response, SSa induced DNA damage, as evidenced by a cytokinesis-block micronucleus assay, single-cell gel electrophoresis, and an increase in the levels of γ-H2AX, a DNA damage marker. Moreover, inhibition of caspase-4 activation inhibited SSa-induced histone H2AX phosphorylation. Taken together, these results suggest that caspase-4 is an upstream regulator of SSa-induced DNA damage and caspase activation in HCC cells. Given that SSa-induced apoptosis appeared to be specific to certain cell types including HCC cells, SSa may be a promising cancer therapy agent in certain types of cancer.en-USsaikosaponin a (SSa)human colon carcinoma (HCC)endoplasmic reticulum (ER) stresscaspase-4DNA damageJournal Article2018-01-1810.18632/oncotarget.22247