title: Characterization of receptors for recombinant human tumor necrosis factor-alpha from human placental membranes.
abstract: High affinity receptors for recombinant human tumor necrosis factor-alpha (rhTNF-alpha) were identified on membranes prepared from full term human placenta. Highly purified rhTNF-alpha iodinated by the iodogen method was found to bind placental membranes in a displaceable manner with an approximate dissociation constant (KD) of 1.9 nM. The membrane bound TNF-alpha receptor could be solubilized by several detergents with optimum extraction being obtained with 1% Triton X-100. The binding of 125I-rhTNF-alpha to the solubilized receptor was found to be time and temperature dependent, yielding maximum binding within 1 h, 24 h and 48 h at 37 degrees C, 24 degrees C and 4 degrees C, respectively. However, the maximum binding obtainable at 4 degrees C was only 40% of that at 37 degrees C. The binding 125I-rhTNF-alpha to solubilized placental membrane extracts was displaceable by unlabeled rhTNF-alpha, but not by a related protein recombinant human tumor necrosis factor-beta (rhTNF-beta; previously called lymphotoxin). This is similar to the behavior of TNF-alpha receptors derived from detergent-solubilized cell extracts, although on intact cells, both rhTNF-alpha and rhTNF-beta bind with equal affinity to TNF receptors. The Scatchard analysis of the binding data of the solubilized receptor revealed high affinity binding sites with a KD of approximately 0.5 nM and a receptor concentration of about 1 pmole/mg protein. Gel filtration of the solubilized receptor-ligand complexes on Sephacryl S-300 revealed two different peaks of radioactivity at approximate molecular masses of 50,000 Da and 400,000 Da. The 400,000 dalton peak corresponded to the receptor-ligand complex. Overall, our results suggest that high affinity receptors for TNF-alpha are present on human placental membranes and provide evidence that these receptors may be different from that of rhTNF-beta.
authors.affiliation: Department of Cardiovascular Research, Genentech, Inc., South San Francisco, CA.
authors.forename: R A
authors.initials: RA
authors.lastname: Aiyer
authors.forename: B B
authors.initials: BB
authors.lastname: Aggarwal
mesh_terms: D001665:Binding Sites; D001667:Binding, Competitive; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D007526:Isoelectric Point; D007700:Kinetics; D008566:Membranes / Q000378:metabolism; D008970:Molecular Weight; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011956:Receptors, Cell Surface / Q000302:isolation & purification / Q000378:metabolism*; D018124:Receptors, Tumor Necrosis Factor; D012995:Solubility; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
chemical_list: D007457:Iodine Radioisotopes; D011956:Receptors, Cell Surface; D018124:Receptors, Tumor Necrosis Factor; D014409:Tumor Necrosis Factor-alpha