Apoptosis is a cell suicide mechanism that enables metazoans to control cell number in tissues and to eliminate individual cells that threaten the animal's survival. Certain cells have unique sensors, termed death receptors, on their surface. Death receptors detect the presence of extracellular death signals and, in response, they rapidly ignite the cell's intrinsic apoptosis machinery.

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Death receptors: signaling and modulation

Osteoprotegerin Ligand Is a Cytokine that Regulates Osteoclast Differentiation and Activation

Sixteen years have passed since the description of the nuclear factor-кB (NF-кB) as a regulator of к light-chain gene expression in murine B lymphocytes (Sen & Baltimore, 1986a) During that time, over 4,000 publications have appeared, characterizing the family of Rel/NF-кB transcription factors involved in the control of a large number of normal and pathological cellular processes The physiological functions of NF-кB proteins include immunological and inflammatory responses, developmental processes, cellular growth and modulating effects on apoptosis In addition, these factors are activated in a number of diseases, including cancer, arthritis, acute and chronic inflammatory states, asthma, as well as neurodegenerative and heart diseases

Activators and target genes of Rel/NF-kappaB transcription factors.

Two different tumour-necrosis factors (TNFs), first isolated in 1984, were found to be cytotoxic to tumour cells and to induce tumour regression in mice. Research during the past two decades has shown the existence of a superfamily of TNF proteins consisting of 19 members that signal through 29 receptors. These ligands, while regulating normal functions such as immune responses, haematopoiesis and morphogenesis, have also been implicated in tumorigenesis, transplant rejection, septic shock, viral replication, bone resorption, rheumatoid arthritis and diabetes; so indicating their role as 'double-edged swords'. These cytokines either induce cellular proliferation, survival, differentiation or apoptosis. Blockers of TNF have been approved for human use in treating TNF-linked autoimmune diseases in the United States and other countries.

/pdf/signalling-pathways-of-the-tnf-superfamily-a-double-edged-aixlu7oo9e.pdf

Signalling pathways of the TNF superfamily: a double-edged sword.

To evaluate the utility of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) as a cancer therapeutic, we created leucine zipper (LZ) forms of human (hu) and murine (mu) TRAIL to promote and stabilize the formation of trimers. Both were biologically active, inducing apoptosis of both human and murine target cells in vitro with similar specific activities. In contrast to the fulminant hepatotoxicity of LZ-huCD95L in vivo, administration of either LZ-huTRAIL or LZ-muTRAIL did not seem toxic to normal tissues of mice. Finally, repeated treatments with LZ-huTRAIL actively suppressed growth of the TRAIL-sensitive human mammary adenocarcinoma cell line MDA-231 in CB.17 (SCID) mice, and histologic examination of tumors from SCID mice treated with LZ-huTRAIL demonstrated clear areas of apoptotic necrosis within 9-12 hours of injection.

Tumoricidal activity of tumor necrosis factor-related apoptosis-inducing ligand in vivo

Identification and characterization of a new member of the TNF family that induces apoptosis

The Novel Receptor TRAIL-R4 Induces NF-κB and Protects against TRAIL-Mediated Apoptosis, yet Retains an Incomplete Death Domain

TRAIL-R3, a new member of the TRAIL receptor family, has been cloned and characterized. TRAIL-R3 encodes a 299 amino acid protein with 58 and 54% overall identity to TRAIL-R1 and -R2, respectively. Transient expression and quantitative binding studies show TRAIL-R3 to be a plasma membrane–bound protein capable of high affinity interaction with the TRAIL ligand. The TRAIL-R3 gene maps to human chromosome 8p22-21, clustered with the genes encoding two other TRAIL receptors. In contrast to TRAIL-R1 and -R2, this receptor shows restricted expression, with transcripts detectable only in peripheral blood lymphocytes and spleen. The structure of TRAIL-R3 is unique when compared to the other TRAIL receptors in that it lacks a cytoplasmic domain and appears to be glycosyl-phosphatidylinositol–linked. Moreover, unlike TRAIL-R1 and -R2, in a transient overexpression system TRAIL-R3 does not induce apoptosis.

https://rupress.org/jem/article-pdf/186/7/1165/1114254/97-1274.pdf

Cloning and characterization of TRAIL-R3, a novel member of the emerging TRAIL receptor family.

Poxvirus Genomes Encode a Secreted, Soluble Protein That Preferentially Inhibits β Chemokine Activity yet Lacks Sequence Homology to Known Chemokine Receptors☆

Pamela J. Smolak

Papers

Identification and characterization of a new member of the TNF family that induces apoptosis

The Novel Receptor TRAIL-R4 Induces NF-κB and Protects against TRAIL-Mediated Apoptosis, yet Retains an Incomplete Death Domain

Cloning and characterization of TRAIL-R3, a novel member of the emerging TRAIL receptor family.

Poxvirus Genomes Encode a Secreted, Soluble Protein That Preferentially Inhibits β Chemokine Activity yet Lacks Sequence Homology to Known Chemokine Receptors☆

Cowpox Virus Genome Encodes a Second Soluble Homologue of Cellular TNF Receptors, Distinct from CrmB, That Binds TNF but Not LTα