title: Bone marrow stroma confers resistance to Apo2 ligand/TRAIL in multiple myeloma in part by regulating c-FLIP.
abstract: Apo2 ligand (Apo2L)/TRAIL induces apoptosis of cancer cells that express the specific receptors while sparing normal cells. Because the tumor microenvironment protects myeloma from chemotherapy, we investigated whether hemopoietic stroma induces resistance to Apo2L/TRAIL apoptosis in this disease. Apo2L/TRAIL-induced death was diminished in myeloma cell lines (RPMI 8226, U266, and MM1s) directly adhered to a human immortalized HS5 stroma cell line but not adhered to fibronectin. In a Transwell assay, with myeloma in the upper well and HS5 cells in the lower well, Apo2L/TRAIL apoptosis was reduced when compared with cells exposed to medium in the lower well. Using HS5 and myeloma patients' stroma-conditioned medium, we determined that soluble factor(s) produced by stroma-myeloma interactions are responsible for a reversible Apo2/TRAIL apoptosis resistance. Soluble factor(s) attenuated procaspase-8, procaspase-3, and poly(ADP-ribose) polymerase cleavage and diminished mitochondrial membrane potential changes without affecting Bcl-2 family proteins and/or Apo2L/TRAIL receptors. Soluble factor(s) increased the baseline levels of the anti-apoptotic protein c-FLIP in all cell lines tested. Inhibition of c-FLIP by means of RNA interference increased Apo2/TRAIL sensitivity in RPMI 8226 cells. Unlike direct adhesion to fibronectin, soluble factor(s) have no impact on c-FLIP redistribution within cellular compartments. Cyclohexamide restored Apo2L/TRAIL sensitivity in association with down-regulation of c-FLIP, suggesting that c-FLIP synthesis, not intracellular traffic, is essential for soluble factor(s) to regulate c-FLIP. Additionally, IL-6 conferred resistance to Apo2L/TRAIL-mediated apoptosis in association with increased c-FLIP levels. In conclusion, the immune cytotoxic effect of Apo2L/TRAIL can be restored at least in part by c-FLIP pathway inhibitors.
authors.affiliation: Blood and Marrow Transplantation Program, H. Lee Moffitt Cancer Center and Research Institute, 12902 Magnolia Drive, Tampa, FL 33612, USA. lia.perez@moffitt.org
authors.forename: Lia Elena
authors.initials: LE
authors.lastname: Perez
authors.forename: Nancy
authors.initials: N
authors.lastname: Parquet
authors.forename: Kenneth
authors.initials: K
authors.lastname: Shain
authors.forename: Ramadevi
authors.initials: R
authors.lastname: Nimmanapalli
authors.forename: Melissa
authors.initials: M
authors.lastname: Alsina
authors.forename: Claudio
authors.initials: C
authors.lastname: Anasetti
authors.forename: William
authors.initials: W
authors.lastname: Dalton
mesh_terms: D017209:Apoptosis; D001853:Bone Marrow / Q000276:immunology*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002448:Cell Adhesion; D045744:Cell Line, Tumor; D003602:Cytotoxicity, Immunologic; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism / Q000494:pharmacology; D009101:Multiple Myeloma / Q000276:immunology*; D034622:RNA Interference; D017154:Stromal Cells / Q000276:immunology; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology*; D000093242:Interleukin-6 Inhibitors
chemical_list: D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D015850:Interleukin-6; D053221:TNF-Related Apoptosis-Inducing Ligand; D000093242:Interleukin-6 Inhibitors; C506386:CFLAR protein, human