Caspase-4 is essential for saikosaponin a-induced apoptosis acting upstream of caspase-2 and γ-H2AX in colon cancer cells

Abstract

Saikosaponin 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.

Localization of malonyl and acetyl on substituted saikosaponins according to the full‐scan mass spectra and the fragmentation of sodium‐adduct ions in the positive mode

“…Saikosaponins exert significant pharmacological activities, including antitumor, chemosensitizing, radiosensitizing, anti‐inflammatory, hepatoprotective, nephroprotective, anti‐Alzheimer, neuroprotective, immune‐modulatory, anti‐virus, and so on. Saikosaponins are considered to be the major bioactive ingredients and the key markers for quality control of Radix Bupleuri , which is a famous traditional Chinese medicine (TCM) that has been used for more than 1000 years.…”

Identification of lncRNA prognostic signature and analysis of their functions for HCV-related hepatocellular carcinoma

“…Excessive DNA damage may induce γ-H2AX-positive cells to undergo apoptosis and exert protective roles [40]. Also, Saikosaponin a (SSa) was reported to induce caspase-mediated apoptosis in human colon carcinoma cells by triggering DNA damage, as evidenced by an increase in the levels of γ-H2AX [41]. Thus, TSSK6 may inhibit HCV-HCC progression by [45].…”

A comprehensive review and perspectives on pharmacology and toxicology of saikosaponins

“…SSa, SSd, 6″-O-acetylsaikosaponin-d and 23-hydroxy-13β, 28β-epoxy-olean-11-ene-16-one-3-O-β-d-glu-copyranosyl-(1→3)-β-d-fucopyranoside exhibit more potent cytotoxicity than other SS derivatives, and are even more cytotoxic against human hepatoma HepG2 cells and human lung cancer A549 cells than the positive control, 5-fluorouracil . A recent study suggested that human colon cancer cells, but not lung cancer, breast cancer and leukemia cells, are sensitive to SSa-induced apoptosis (Kang et al, 2017). Caspase-4 and downstream sequential caspase-2/caspase-8 activation is suggested to be essential for anticancer effects of SSa on human colon cancer cell lines (Kang et al, 2017;Kim and Hong, 2011).…”

“…A recent study suggested that human colon cancer cells, but not lung cancer, breast cancer and leukemia cells, are sensitive to SSa-induced apoptosis (Kang et al, 2017). Caspase-4 and downstream sequential caspase-2/caspase-8 activation is suggested to be essential for anticancer effects of SSa on human colon cancer cell lines (Kang et al, 2017;Kim and Hong, 2011). Several studies further suggested that SSa induces apoptosis in human breast MDA-MB-231 and MCF-7 cells via p53/p21 independent and dependent mechanisms respectively and inhibits the growth of HepG2 by induction of CDK inhibitors Wu and Hsu, 2001).…”