Impaired activation of caspases and prevention of mitochondrial dysfunction in the metastatic colon carcinoma CC531s-m2 cell line

In a previous paper we described the properties of a rapidly metastasizing cell line CC531s-m2 derived from the poorly metastasizing CC531s cell. The m2-cell line was relatively resistant to killing by NK cells. Both CD95L and TRAIL mediated apoptosis was decreased in the m2-cell line. Now, by flow cytometrical analysis of intra- and extra-cellular expressed receptors, we show that the localization of the receptors for CD95L and TRAIL was not altered in the CC531s-m2 cells as compared to the parental cell line. Subsequently caspase-activation and mitochondrial function were studied by enzymatic cleavage of fluorescent caspase-substrates and retention of the mitochondrial dye rhodamine-123, respectively. The activation of caspases as well as the loss of the mitochondrial membrane potential (MMP) was less in the CC531s-m2 cell line upon CD95L- and TRAIL-signalling. Furthermore, the sensitivity of the CC531-m2 towards cisplatin-induced apoptosis was strongly decreased. This was consistent with less mitochondrial damage, delayed caspase cleavage and decreased caspase activity. Altogether, we conclude that an Natural Killer-cell insensitive cell is less sensitive to CD95L- and TRAIL-induced apoptosis as well as anti-cancer drug induced apoptosis by prevention of mitochondrial damage and activation of caspases.