Recombinant human TNF-α (rhTNF-α) potentiates paclitaxel-induced apoptosis.

(A) U937 cells were treated with paclitaxel (5 nM) with or without rhTNF (0 to 0.1 ng/mL) for 24 hours. (B) U937/neo (░) and U937/ΔBcl-2 (▪) were treated with paclitaxel (5 nM) with or without rhTNF (0.025 ng/mL) for 24 hours. Apoptotic cells were quantified by annexin V and PI positivity as described in “Materials and methods.” Data are shown in panels A and B as the means ± SE. *Significant difference compared with paclitaxel alone or TNF-α alone treatment in the corresponding cell lines (P < .025). (C) Cells were exposed to paclitaxel with or without rhTNF as in panel B, after which the degradation of native procaspase-8 and expression of cytosolic cytochrome c were monitored by Western analysis as described in “Materials and methods.” Blots were reprobed for actin to ensure equal protein loading and transfer. Two additional experiments yielded similar results.