Resistance to TRAIL in non-transformed cells is due to multiple redundant pathways

Abstract

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a cytokine and a selective inducer of apoptosis in a range of tumour cells, but not in normal, untransformed cells. A large number of chemotherapeutics as well as biological agents are being tested for their potential to sensitise resistant tumour cells to TRAIL as a means to broaden the range of tumours treatable with TRAIL. However, because of the incomplete understanding of the mechanism(s) underlying TRAIL resistance in non-malignant cells, it is unpredictable whether the effect of these sensitisers will be restricted to tumour cells or they would also sensitise non-transformed cells causing unwanted toxicity. In this study, we carried out a systematic analysis of the mechanisms driving TRAIL resistance in non-transformed cells. We found that cellular FLICE-like inhibitory protein, anti-apoptotic B-cell lymphoma 2 proteins, and X-linked inhibitor of apoptosis protein were independently able to provide resistance to TRAIL. Deficiency of only one of these proteins was not sufficient to elicit TRAIL sensitivity, demonstrating that in non-transformed cells multiple pathways control TRAIL resistance and they act in a redundant manner. This is contrary to the resistance mechanisms found in tumour cell types, many of them tend to rely on a single mechanism of resistance. Supporting this notion we found that 76% of TRAIL-resistant cell lines (13 out of 17) expressed only one of the above-identified anti-apoptotic proteins at a high level (≥1.2-fold higher than the mean expression across all cell lines). Furthermore, inhibition or knockdown of the single overexpressed protein in these tumour cells was sufficient to trigger TRAIL sensitivity. Therefore, the redundancy in resistance pathways in non-transformed cells may offer a safe therapeutic window for TRAIL-based combination therapies where selective sensitisation of the tumour to TRAIL can be achieved by targeting the single non-redundant resistance pathway.

The Deubiquitinase Inhibitor PR-619 Sensitizes Normal Human Fibroblasts to Tumor Necrosis Factor-related Apoptosis-inducing Ligand (TRAIL)-mediated Cell Death

“…However, the mechanism(s) that lead to normal cell TRAIL resistance have yet to be fully characterized. Van Dijk et al (37) have previously investigated TRAIL resistance in non-transformed primary dermal fibroblasts and umbilical artery smooth muscle cells. They found that multiple pathways control TRAIL resistance in normal cells.…”

“…They found that multiple pathways control TRAIL resistance in normal cells. c-FLIP, Bcl-2, and X-linked inhibitor of apoptosis protein have all been found to provide resistance to normal cells and act in a redundant manner (37).…”

Decoy receptors block TRAIL sensitivity at a supracellular level: the role of stromal cells in controlling tumour TRAIL sensitivity

“…[14][15][16] For example, DcR1 was found to be the strongest single predictor of overall survival in AML 17 and in vitro overexpression of DcRs protected tumour cells from TRAIL-induced apoptosis. On the contrary, DcR expression in the tumour does not correlate with TRAIL sensitivity 18,19 and non-transformed cells do not require DcRs to be protected from TRAIL-induced apoptosis, 20 suggesting that the in vivo role of the DcRs may be more complex than originally thought. In this study, we examined the hypothesis that DcRs exert a 'tissue-level control' of TRAIL sensitivity rather than simply regulating TRAIL resistance at a cell autonomous level.…”

G2/M Arrest Sensitises Erythroid Leukemia Cells to TRAIL-induced Apoptosis

“…Cells were harvested by centrifugation, lysed, denatured and proteins separated and blotted as described before [6]. Blots were incubated with rabbit polyclonal antibodies against caspase-3 (1:1 000; Cell Signaling Technologies, Danvers, MA, USA), Mcl-1 (1:1 000; Cell Signaling Technologies), Cyclin E (1:1 000, Sigma), Cyclin B1 (1:1 000, ThermoScientific),or actin (1:500; Sigma) and mouse monoclonal antibodies against caspase-8 1C12 ( …”

“…Recent studies however identified drug combination strategies that could potently sensitize TRAIL-resistant tumours [6]. Additionally, a recent study on acute lymphocytic leukemia has shown that the undifferentiated leukemiainitiating cell (LIC) population is sensitive to TRAIL and tumour extracts from TRAIL-treated xenografts fail to re-establish the tumour when transplanted into a new animal [7] highlighting the possible potential of TRAIL for targeting the undifferentiated cells driving erythroid leukemia.…”