Camptothecin Fails to Induce Apoptosis in Tumor Necrosis Factor-Alpha-Treated HaCaT Cells

Abstract

Camptothecin (CPT), a DNA topoisomerase I inhibitor, was originally isolated from the fruits of the Chinese Camptotheca acuminata tree. CPT and its derivatives have been used in the treatment of psoriasis and cancer in China for decades. It is well known that tumor necrosis factor-α (TNF-α) is a key proinflammatory cytokine in the pathogenesis of psoriasis. In this study, we investigated the effect of CPT on TNF-α-treated HaCaT cells. The results indicated that CPT in the concentration range of 0.5–2.0 µg·ml^–1 failed to show any proapoptotic effect in HaCaT cells. It was found that both CPT and TNF-α up-regulated the expression of TRAIL receptor 1/2 but not TRAIL in HaCaT cells. Furthermore, the expression of antiapoptotic proteins (IAP1, IAP2, and Bcl-X_L) was up-regulated by TNF-α and suppressed by CPT in HaCaT cells. Because these gene products are known to be regulated by nuclear factor-kappa B (NF-ĸB), we examined the role of CPT on NF-ĸB activation. It was found that CPT not only failed to inhibit TNF-α-induced NF-ĸB activation but also contributed to NF-ĸB activation. In addition to these effects, CPT also promoted the production of interleukin-6, similar to TNF-α, in HaCaT cells. In conclusion, despite ample evidence supporting CPT-induced carcinoma cell apoptosis, our study clearly shows that CPT fails to show any proapoptotic effects in HaCaT cells, even though it enhanced TRAIL receptor 1/2 expression and inhibited the expression of TNF-α-induced antiapoptotic proteins. Taken together, this study demonstrates that CPT fails to block the activity of TNF-α. With respect to the NF-ĸB-activating role of CPT, we suggest that the benefit of CPT in the treatment of psoriasis should be reevaluated.