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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.〔 *Lymphotoxin-alpha, formerly known as Tumor necrosis factor-beta (TNF-β), is a cytokine that is inhibited by interleukin 10. ==Family members== 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 〔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)〕 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. * Lymphotoxin-alpha (LT-alpha) and lymphotoxin-beta (LT-beta), two related cytokines produced by lymphocytes that are cytotoxic for a wide range of tumor cells in vitro and in vivo. * 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.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tumor necrosis factors」の詳細全文を読む スポンサード リンク
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