Proteasome Inhibition Results in TRAIL Sensitization of Primary Keratinocytes by Removing the Resistance-Mediating Block of Effector Caspase Maturation

Enhanced caspase-8 recruitment to and activation at the DISC is critical for sensitisation of human hepatocellular carcinoma cells to TRAIL-induced apoptosis by chemotherapeutic drugs

“…Three independent experiments with similar results have been performed directly activated at the DISC to discriminate caspase-8 activation secondary to a mitochondrial amplification loop. 30,61 Postmitochondrial changes as described by Leverkus et al 58 were not observed in these cell lines, as we found no change in the expression of IAPs after incubation with 5-FU (data not shown). However, the HCC cells sensitised with 5-FU recruited massive caspase-8 at the native DISC already after 15 min.…”

“…54 Recently, it has been shown that in a number of cell types TRAIL-induced apoptosis requires Bax-dependent release of Smac/DIABLO to achieve inactivation of the inhibitor of apoptosis proteins (IAPs). [57][58][59][60] To test whether sensitisation in HCC cells to TRAIL-induced apoptosis is a receptorproximal event or whether it is regulated further downstream in the apoptotic signalling cascade, we examined the kinetics of cleavage of the initiator caspase-8. In contrast to resistant cells, we found massive and early caspase-8 cleavage in the sensitised cells with a maximum detected in the lysates after 1-2 h. Next, we tested whether caspase-8 activation was Figure 7 Enhanced caspase-8 and constant levels of cFLIP recruitment revealed by native TRAIL DISC analysis after sensitisation with 5-FU.…”

Induction of apoptosis in experimental human B cell lymphomas by conditional TRAIL-expressing T cells

“…Furthermore, tumoricidal activity of TRAIL in vivo is enhanced when combined with chemotherapeutic agents, ionising radiation or Smac peptides (Nagane et al, 2001;Fulda et al, 2002;Munshi et al, 2002). Surprisingly, previous investigators have reported the toxic effects of TRAIL also on normal primary human cells, including hepatocytes (Jo et al, 2000), keratinocytes (Leverkus et al, 2003) and endothelial cells (Li et al, 2003). The basis of this difference is unclear, but could result from the methods used to assess cell death or problems in preparation of the respective recombinant TRAIL used in these particular studies (Lawrence et al, 2001).…”

“…The basis of this difference is unclear, but could result from the methods used to assess cell death or problems in preparation of the respective recombinant TRAIL used in these particular studies (Lawrence et al, 2001). Also, primary keratinocytes are relatively resistant and become first sensitive by inhibition of the proteasome (Leverkus et al, 2003). In this regard, the effects of TRAIL-induced injury in primary endothelial cells are not unique.…”

Modulation of tumor necrosis factor related apoptosis-inducing ligand (TRAIL) receptors in a human osteoclast model in vitro

“…XIAP, briefly discussed above, is highly expressed in primary cells but significantly reduced in transformed cells, allowing for its inhibition to result in caspase-3 cleavage, helping trigger apoptotic cascades (Leverkus et al, 2003). Other potential mechanisms by which proteasome inhibitors could sensitize cells to TRAIL include repression of c-FLIP and/or p53, or by inducing caspase and Bax expression .…”