Oncogenic Ras sensitizes normal human cells to tumor necrosis factor-alpha-related apoptosis-inducing ligand-induced apoptosis.
Tumor necrosis factor-alpha-related apoptosis-inducing ligand (TRAIL) is a cytotoxic cytokine that induces apoptosis in tumor cells but rarely kills normal ones. To determine how normal human cells acquire TRAIL-sensitive phenotype during the process of malignant transformation, we used an experimental system that allows for controlled conversion of human cells from normal to cancerous by introduction of several genes. Human embryonic kidney cells and foreskin fibroblasts were first immortalized by combination of the early region of simian virus 40 and telomerase and then were transformed with oncogenic Ras. Both normal and immortalized cells were resistant to TRAIL-induced apoptosis, whereas Ras-transformed cells were susceptible. Ras transformation enhanced TRAIL-induced activation of caspase 8 by increasing its recruitment to TRAIL receptors. The proapoptotic effects of Ras could be reversed by mutations in its effector loop or by inhibitors of either farnesyl transferase or mitogen-activated protein kinase kinase. The expression of constitutively activated mitogen-activated protein kinase kinase 1 enhanced caspase 8 recruitment and sensitized immortalized human embryonic kidney cells to TRAIL-induced death. These results indicate that in normal human cells the TRAIL-induced apoptotic signal is blocked at the level of caspase 8 recruitment and that this block can be eliminated by Ras transformation, involving activation of the mitogen-activated protein kinase pathway.
Nesterov
Alexandre
A
Division of Medical Oncology, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA.
Nikrad
Malti
M
Johnson
Thomas
T
Kraft
Andrew S
AS
D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D051017:Apoptosis Regulatory Proteins; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism; D002471:Cell Transformation, Neoplastic / Q000235:genetics* / Q000473:pathology; D002478:Cells, Cultured; D053418:Death Domain Receptor Signaling Adaptor Proteins; D004789:Enzyme Activation / Q000187:drug effects; D011905:Genes, ras / Q000502:physiology*; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008562:Membrane Glycoproteins / Q000378:metabolism / Q000494:pharmacology*; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism; D053221:TNF-Related Apoptosis-Inducing Ligand; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism / Q000494:pharmacology*
D051017:Apoptosis Regulatory Proteins; D053418:Death Domain Receptor Signaling Adaptor Proteins; D008562:Membrane Glycoproteins; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D018124:Receptors, Tumor Necrosis Factor; D053221:TNF-Related Apoptosis-Inducing Ligand; C105190:TNFRSF10A protein, human; C505639:TNFRSF10B protein, human; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha; C505530:CASP8 protein, human; D053181:Caspase 8; D020169:Caspases