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Molecular determinants of response to TRAIL in killing of normal and cancer cells
1Howard Hughes Medical Institute, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia 19104, USA.
Abstract:
The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL or Apo2L) is a potent inducer of death of cancer but not normal cells, which suggests its potential use as a tumor-specific antineoplastic agent. TRAIL binds to the proapoptotic death receptors DR4 and the p53-regulated proapoptotic KILLER/DR5 as well as to the decoy receptors TRID and TRUNDD. In the present studies, we identified a subgroup of TRAIL-resistant cancer cell lines characterized by low or absent basal DR4 or high expression of the caspase activation inhibitor FLIP. Four of five TRAIL-sensitive cell lines expressed high levels of DR4 mRNA and protein, whereas six of six TRAIL-resistant cell lines expressed low or undetectable levels of DR4 (chi 2; P < 0.01). FLIP expression appeared elevated in five of six (83%) TRAIL-resistant cell lines and only one of five (20%) TRAIL-sensitive cells (chi 2; P < 0.05). Two TRAIL-resistant lines that expressed DR4 contained an A-to-G alteration in the death domain encoding arginine instead of lysine at codon 441. The K441R polymorphism is present in 20% of the normal population and can inhibit DR4-mediated cell killing in a dominant-negative fashion. The expression level of KILLER/DR5, TRID, TRUNDD or TRID, and TRUNDD did not correlate with TRAIL sensitivity (P > 0.05). These results suggest that the major determinants for TRAIL sensitivity may be the expression level of DR4 and FLIP. TRAIL-resistant cells became susceptible to TRAIL-mediated apoptosis in the presence of doxorubicin. In TRAIL-sensitive cells, caspases 8, 9, and 3 were activated after TRAIL treatment, but in TRAIL-resistant cells, they were activated only by the combination of TRAIL and doxorubicin. Our results suggest: (a) evaluation of tumor DR4 and FLIP expression and host DR4 codon 441 status could be potentially useful predictors of TRAIL sensitivity, and (b) doxorubicin, in combination with TRAIL, may effectively promote caspase activation in TRAIL-resistant tumors.
Insights
Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) effectively targets cancer cells. TRAIL resistance is linked to low DR4 or high FLIP expression, but can be overcome with doxorubicin.
Area of Science:
- Molecular Biology
- Cancer Research
- Apoptosis
Background:
- Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces cancer cell death but not normal cell death, showing potential as an antineoplastic agent.
- TRAIL interacts with proapoptotic death receptors (DR4, KILLER/DR5) and decoy receptors (TRID, TRUNDD).
Purpose of the Study:
- To identify mechanisms of TRAIL resistance in cancer cell lines.
- To explore strategies for overcoming TRAIL resistance.
Main Methods:
- Assessed TRAIL sensitivity in cancer cell lines.
- Quantified expression levels of DR4, FLIP, KILLER/DR5, TRID, and TRUNDD.
- Investigated the impact of doxorubicin in combination with TRAIL on TRAIL-resistant cells.
Main Results:
- TRAIL-resistant cell lines exhibited low/absent DR4 expression or high FLIP expression.
- A DR4 polymorphism (K441R) was identified in some TRAIL-resistant lines, inhibiting DR4-mediated killing.
- Doxorubicin sensitized TRAIL-resistant cells to TRAIL-induced apoptosis by promoting caspase activation.
Conclusions:
- DR4 expression levels, FLIP expression, and the DR4 K441R polymorphism are potential predictors of TRAIL sensitivity.
- Combining TRAIL with doxorubicin may be an effective strategy to treat TRAIL-resistant tumors.