Trimeric structure of TNF alpha, produced by Mus musculus, based on PDB structure 2TNF (1.4 Å Resolution). Different colors represent different monomers. Baeyens, KJ et al. (1999). Figure rendered using FirstGlance Jmol.
Tumor necrosis factors (or the TNF family) refer to a group of cytokines that can cause cell death (apoptosis). The first two members of the family to be identified were:
Tumor necrosis factor (TNF), formerly known as TNFα or TNF alpha, is the best-known member of this class. TNF is a monocyte-derived cytotoxin that has been implicated in tumor regression, septic shock, and cachexia. The protein is synthesized as a prohormone with an unusually long and atypical signal sequence, which is absent from the mature secreted cytokine. A short hydrophobic stretch of amino acids serves to anchor the prohormone in lipid bilayers. Both the mature protein and a partially processed form of the hormone can be secreted after cleavage of the propeptide.
Nineteen proteins have been identified as part of the TNF family on the basis of sequence, functional, and structural similarities. They include:
Tumor Necrosis Factor (TNF) (also known as cachectin  or TNF alpha) is a cytokine that has a wide variety of functions. It can cause cytolysis of certain tumor cell lines; it is involved in the induction of cachexia; it is a potent pyrogen, causing fever by direct action or by stimulation of interleukin-1 secretion; it can stimulate cell proliferation and induce cell differentiation under certain conditions.
T cell antigen gp39 (CD40L), a cytokine that seems to be important in B-cell development and activation.
CD27L, a cytokine that plays a role in T-cell activation. It induces the proliferation of co-stimulated T cells and enhances the generation of cytolytic T cells.
CD30L, a cytokine that induces proliferation of T cells.
FASL, a cell surface protein involved in cell death.
4-1BBL, an inducible T cell surface molecule that contributes to T-cell stimulation.
OX40L, a cell surface protein that co-stimulates T cell proliferation and cytokine production.
TNF-related apoptosis inducing ligand (TRAIL), a cytokine that induces apoptosis.
All these cytokines seem to form homotrimeric (or heterotrimeric in the case of LT-alpha/beta) complexes that are recognized by their specific receptors. Strong hydrogen bonds between the monomers stabilize the tertiary structure. One such example is the Asn34-Arg82 hydrogen bond in the M. musculus TNF alpha. The PROSITE pattern for this family is located in a beta-strand in the central section of the protein that is conserved across all members.
All members of the TNF family, with the exception of the secreted lymphotoxin and a proliferation-inducing ligand (APRIL), are type II transmembrane proteins that protrude from immune cells. Such membrane-bound TNF ligands frequently signal back to the immune cells when they contact and bind their cognate receptors on other cells.
^ abcBaeyens KJ, De Bondt HL, Raeymaekers A, Fiers W, De Ranter CJ (April 1999). "The structure of mouse tumour-necrosis factor at 1.4 Å resolution: towards modulation of its selectivity and trimerization". Acta Crystallogr. D Biol. Crystallogr.55 (Pt 4): 772–8. doi:10.1107/s0907444998018435. PMID10089307.
^Kriegler M, Perez C, DeFay K, Albert I, Lu SD (April 1988). "A novel form of TNF/cachectin is a cell surface cytotoxic transmembrane protein: ramifications for the complex physiology of TNF". Cell53 (1): 45–53. doi:10.1016/0092-8674(88)90486-2. PMID3349526.
^Sherry B, Jue DM, Zentella A, Cerami A (December 1990). "Characterization of high molecular weight glycosylated forms of murine tumor necrosis factor". Biochem. Biophys. Res. Commun.173 (3): 1072–8. doi:10.1016/S0006-291X(05)80895-2. PMID2268312.
^ abCseh K, Beutler B (September 1989). "Alternative cleavage of the cachectin/tumor necrosis factor propeptide results in a larger, inactive form of secreted protein". J. Biol. Chem.264 (27): 16256–60. PMID2777790.
^Waltenbaugh C, Doan T, Melvold R, Viselli S (2008). Immunology. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins. p. 68. ISBN0-7817-9543-5.
^Peitsch MC, Jongeneel CV (February 1993). "A 3-D model for the CD40 ligand predicts that it is a compact trimer similar to the tumor necrosis factors". Int. Immunol.5 (2): 233–8. doi:10.1093/intimm/5.2.233. PMID8095800.
^D. CAPUT, et al., Identification of a common nucleotide sequence in the 3'-untranslated region of mRNA molecules specifying inflammatory mediators, Proc. Natl. Acad. Sci. USA 83:1670-1674 Biochemistry, 1986 and references cited)
^Vilcek J, Lee TH (April 1991). "Tumor necrosis factor. New insights into the molecular mechanisms of its multiple actions". J. Biol. Chem.266 (12): 7313–6. PMID1850405.
^Browning JL, Ngam-ek A, Lawton P, DeMarinis J, Tizard R, Chow EP, Hession C, O'Brine-Greco B, Foley SF, Ware CF (March 1993). "Lymphotoxin beta, a novel member of the TNF family that forms a heteromeric complex with lymphotoxin on the cell surface". Cell72 (6): 847–56. doi:10.1016/0092-8674(93)90574-A. PMID7916655.
^Suda T, Takahashi T, Golstein P, Nagata S (December 1993). "Molecular cloning and expression of the Fas ligand, a novel member of the tumor necrosis factor family". Cell75 (6): 1169–78. doi:10.1016/0092-8674(93)90326-L. PMID7505205.
^Wiley SR, Schooley K, Smolak PJ, Din WS, Huang CP, Nicholl JK, Sutherland GR, Smith TD, Rauch C, Smith CA (December 1995). "Identification and characterization of a new member of the TNF family that induces apoptosis". Immunity3 (6): 673–82. doi:10.1016/1074-7613(95)90057-8. PMID8777713.