Apoptosis/physiology; Proteins/physiology; Tumor Necrosis Factor-alpha/physiology; Amino Acid Chloromethyl Ketones/pharmacology; Animals; Antigens, CD/drug effects; Apoptosis/drug effects; Caspases/metabolism; Cell Line, Transformed; Cells, Cultured/drug effects; Ceramides/biosynthesis; Ceramides/pharmacology; Cysteine Proteinase Inhibitors/pharmacology; Daunorubicin/pharmacology; Enzyme Activation/drug effects; Fibroblasts/cytology; Fibroblasts/drug effects; Genes, Dominant; Humans; Hydrolysis; Intercellular Adhesion Molecule-1/biosynthesis; Intercellular Adhesion Molecule-1/genetics; Intracellular Signaling Peptides and Proteins; MAP Kinase Signaling System/drug effects; Mice; Mice, Knockout; Mitogen-Activated Protein Kinase 1/antagonists & inhibitors; Mitogen-Activated Protein Kinase 1/metabolism; Protein Structure, Tertiary; Proteins/genetics; Receptors, Tumor Necrosis Factor/drug effects; Receptors, Tumor Necrosis Factor, Type I; Recombinant Fusion Proteins/physiology; Second Messenger Systems; Sphingomyelin Phosphodiesterase/metabolism; Sphingomyelins/metabolism; Tumor Necrosis Factor-alpha/pharmacology; Tumor Necrosis Factor-alpha/toxicity; U937 Cells