Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL/Apo2L) is a potent inducer of apoptosis in various cancer cells, whereas normal cells are not sensitive to TRAILmediated apoptosis. Four TRAIL/Apo2L receptors (DR4, DR5, DcR1, and DcR2) have been identified. DR4 and DR5 have a death domain, whereas DcR1 and DcR2 are called decoy receptors because of their incomplete or lack of a death domain. Malignant rhabdoid tumor (MRT) is an aggressive neoplasm showing a poor prognosis because of its resistance to chemotherapeutic agents. In this study, we examined whether TRAIL could induce apoptotic cell death in MRT cell lines. We found that although half of the MRT cell lines examined were sensitive to TRAIL/Apo2L, Western blot analysis revealed that the expression of DcR2 was low in TRAIL-sensitive MRT cells. We examined the effect of doxorubicin on the expression levels of TRAIL receptors and its enhancement on the susceptibility of MRT cell lines to TRAIL. Western blot and flow cytometric analyses revealed that doxorubicin significantly increased the expression of DR5, and somewhat up-regulated the expression of Abbreviations MRT, malignant rhabdoid tumor TNF, tumor necrosis factor TRAIL/Apo2L, tumor necrosis factor-related apoptosis-inducing ligand or Apo2 ligand NF-B, nuclear factor-B PI3-kinase, phosphatidylinositol 3-kinase PI, propidium iodide MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide MRTs were first described in the kidney as a rare variant of Wilms' tumor with a rhabdomyosarcomatoid pattern. Unfortunately, there is no effective treatment for this disease because it is largely resistant to both chemotherapy and radiotherapy. MRT also has an extremely poor prognosis because of its high potential for metastasis (1). Primary MRT has been described in the CNS, pelvis, and paravertebral regions (2-7). A characteristic feature of MRT cells is the presence of a large eosinophilic inclusion in the cytoplasm (8, 9). In the brain, the tumors may present as a mixture of rhabdoid tumor with primitive neuroectodermal tumors, mesenchymal, or epithelial element, an entity referred to as atypical teratoid/rhabdoid tumors (10, 11). Most atypical teratoid/rhabdoid tumors demonstrate monosomy 22 or deletions of chromosome band 22q11 with alterations of the hSNF5/INI1 gene (12). Recently study revealed that MRT has truncated mutations and homozygous deletions of hSNF5/INI1 gene, suggesting a tumor suppressor gene (13).TNF-related apoptosis-inducing ligand or Apo2 ligand (TRAIL/Apo2L) was recently identified as a member of the TNF superfamily of cell death-inducing ligands. This ligand is a type II transmembrane protein that triggers apoptosis mainly in tumor cells (14,15). TRAIL induces apoptotic cell death in many cancer or transformed cells both in vitro and in various in vivo tumor models (16 -20). However, its proapoptotic effects are minimal in normal human cells in vitro and in TRAIL-treated animals (14,(21)(22)(23)(24)(25). TRAIL mRNA is constitutively present in many tissues, unlike the r...