Inhibition of Caspases Increases the Sensitivity of L929 Cells to Necrosis Mediated by Tumor Necrosis Factor

TLDR

Murine L929 fibrosarcoma cells undergo rapid TNF‑induced necrosis driven by excess reactive oxygen intermediates. The study examined whether caspases modulate this TNF‑mediated necrotic pathway. Stabilizing the caspase inhibitor CrmA or treating cells with caspase inhibitors (Ac‑YVAD‑cmk, zDEVD‑fmk, zVAD‑fmk, zD‑fmk) increased TNF sensitivity by ~1,000‑fold, lowered the half‑maximal dose, accelerated ROS production, and this sensitization was abrogated by the antioxidant butylated hydroxyanisole, indicating caspases protect against TNF‑induced ROS and necrosis.

Abstract

Murine L929 fibrosarcoma cells treated with tumor necrosis factor (TNF) rapidly die in a necrotic way, due to excessive formation of reactive oxygen intermediates. We investigated the role of caspases in the necrotic cell death pathway. When the cytokine response modifier A (CrmA), a serpin-like caspase inhibitor of viral origin, was stably overexpressed in L929 cells, the latter became 1,000-fold more sensitive to TNF-mediated cell death. In addition, TNF sensitization was also observed when the cells were pretreated with Ac-YVAD-cmk or zDEVD-fmk, which inhibits caspase-1– and caspase-3–like proteases, respectively. zVAD-fmk and zD-fmk, two broad-spectrum inhibitors of caspases, also rendered the cells more sensitive, since the half-maximal dose for TNF-mediated necrosis decreased by a factor of 1,000. The presence of zVAD-fmk also resulted in a more rapid increase of TNF-mediated production of oxygen radicals. zVAD-fmk–dependent sensitization of TNF cytotoxicity could be completely inhibited by the oxygen radical scavenger butylated hydroxyanisole. These results indicate an involvement of caspases in protection against TNF-induced formation of oxygen radicals and necrosis.