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Inducible Resistance of Tumor Cells to Tumor Necrosis Factor–Related Apoptosis-Inducing Ligand Receptor 2–Mediated Apoptosis by Generation of a Blockade at the Death Domain Function

¹ Department of Cell Biology and Divisions of ² Clinical Immunology and Rheumatology, ³ Gyn Oncology, ⁴ Radiation Biology, and ⁵ Hematology and Oncology, University of Alabama at Birmingham, Birmingham, Alabama

Requests for reprints: Tong Zhou, Department of Cell Biology and Divisions of Clinical Immunology and Rheumatology, University of Alabama at Birmingham, 465 LHRB, 701 South 19th Street, Birmingham, AL 35294. Phone: 205-975-7510; Fax: 205-975-6648; E-mail: tong.zhou{at}ccc.uab.edu.

Induction of tumor cell resistance to therapeutics has been a major obstacle in cancer therapy. Targeting of the death receptors by a natural ligand, tumor necrosis factor–related apoptosis-inducing ligand (TRAIL), or agonistic monoclonal antibodies against TRAIL receptor 1 (TRAIL-R1) or TRAIL receptor 2 (TRAIL-R2) has been thought to be a promising cancer therapy. To determine whether tumor cells are able to generate a resistance to apoptosis induced by an anti-TRAIL-R2 antibody, TRA-8, we examined the apoptotic response of human breast and ovarian cancer cell lines after treatment with TRA-8. Our results show that tumor cell resistance to TRA-8 can be induced by repeated treatment of tumor cells with low, non-apoptosis-inducing doses of TRA-8. Interestingly, the induced resistance to apoptosis was not due to a global apoptotic defect in tumor cells but rather a selective defect in the TRAIL-R2 signaling pathway. Whereas TRA-8-treated tumor cells developed a selective resistance to TRAIL-R2-mediated apoptosis, the apoptotic responses induced by TRAIL, an anti-TRAIL-R1 antibody (2E12), and other apoptotic stimuli were not impaired. The expression levels of cell surface TRAIL-R2 were not altered and mutations of TRAIL-R2 were not found in the resistant cells. The induced TRA-8 resistance was due to a selective blockade at the level of the death domain and could be reversed by a wide array of chemotherapeutic agents. Proteomic analysis of death-inducing signaling complex formation during TRA-8 treatment shows that the translocation of TRAIL-R2-associated apoptotic proteins was significantly altered. Our results suggest that the prevention of tumor cell resistance to therapeutic agents that target the death receptors must be taken into consideration. (Cancer Res 2006; 66(17): 8520-8)