Deficient Tumor Necrosis Factor-related Apoptosis-inducing Ligand (TRAIL) Death Receptor Transport to the Cell Surface in Human Colon Cancer Cells Selected for Resistance to TRAIL-induced Apoptosis

Abstract

Many tumor cell types are sensitive to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. Incubation of TRAIL-sensitive cells with TRAIL invariably leads to resistant survivors even when high doses of TRAIL are used. Because the emergence of resistance to apoptosis is a major concern in successful treatment of cancer, and TRAIL survivors may contribute to therapeutic failure, we investigated potential resistance mechanisms. We selected TRAILresistant SW480 human colon adenocarcinoma cells by repeatedly treating them with high and/or low doses of TRAIL. The resulting TRAIL-resistant clones were not cross-resistant to Fas or paclitaxel. Expression of modulators of apoptosis was not changed in the resistant cells, including TRAIL receptors, cFLIP, Bax, Bid, or IAP proteins. Surprisingly, we found that DISC formation was deficient in multiple selected TRAIL-resistant clones. DR4 was not recruited to the DISC upon TRAIL treatment, and caspase-8 was not activated at the DISC. Although total cellular DR4 mRNA and protein were virtually identical in TRAIL-sensitive parental and TRAIL-resistant clones, DR4 protein expression on the cell surface was essentially undetectable in the TRAILresistant clones. Moreover, exogenous DR4 and KILLER/DR5 were not properly transported to the cell surface in the TRAIL-resistant cells. Interestingly, TRAIL-resistant cells were resensitized to TRAIL by tunicamycin pretreatment, which increased cell surface expression of DR4 and KILLER/DR5. Our data suggest that tumor cells may become resistant to TRAIL through regulation of the death receptor cell surface transport and that resistance to TRAIL may be overcome by the glycosylation inhibitor/endoplasmic reticulum stressinducing agent tunicamycin.

Differential susceptibility to TRAIL of normal versus malignant human urothelial cells

“…Although evolution of colon carcinoma cells with partially deficient TRAIL-R1 transport to the cell surface has recently been described, this only occurred after long-term culture and clonal selection. 39 By contrast, in our study, TRAIL-resistant cell populations arose rapidly, yet recovered receptor expression following removal of TRAIL. It is possible that high concentrations of TRAIL induce a negative-feedback loop which decreases receptor expression in surviving cells.…”

Sodium arsenite accelerates TRAIL-mediated apoptosis in melanoma cells through upregulation of TRAIL-R1/R2 surface levels and downregulation of cFLIP expression

“…Arsenite also affects cytoskeleton functions and promotes TRAIL-R1/R2 translocation from the intracellular pools to cell surface, as it was observed in the present study. The existence of intracellular pools of TRAIL-R1/R2 and a suppression of receptor translocation in some cancer cell lines have been previously described in several publications [66,67]. Surprisingly, many cell types (both normal and cancer) are relatively resistant to cytotoxic effects of low doses of sodium arsenite, thereby making it possible to use this agent as a regulator of cell signaling pathways in different types of combined treatment.…”

Increased sensitivity to TRAIL-induced apoptosis occurs during the adenoma to carcinoma transition of colorectal carcinogenesis

“…The importance of examining cell surface expression of TRAIL receptors has been highlighted recently by Jin et al (2004), who showed that TRAIL-resistant variants of the colon carcinoma cell line SW480 had reduced cell surface expression of TRAIL-R1 compared to the parental cell line, although total protein expression remained unchanged. However, it is interesting that in our study the cell surface expression of the four TRAIL receptors did not correlate with the increased sensitivity to TRAIL that is associated with malignancy.…”