Demonstration of membrane receptors for human natural and recombinant 125I‐labeled tumor necrosis factor on HeLa cell clones and their role in tumor cell sensitivity

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Abstract
Samples of natural and recombinant tumor necrosis factor (TNF) were labelled with 125I by use of Iodobeads and were used to study TNF receptor expression on different HeLa clones. Both labeled preparations retained cytotoxic activity after 125I‐labelling and were indistinguishable from their unlabeled counterparts on sodium dodecylsulfate/polyacrylamide gel electrophoresis. They bound specifically to TNF‐sensitive cells but not to HeLa clones that were resistant to TNF. The binding of 125I‐TNF was competed up to 90% by the addition of non‐radiolabeled TNF. The binding reached a half‐maximal level at 10 pM and saturation at 100 pM. These concentrations approximated those required for cell destruction. Scatchard analysis of the binding data yielded linear plots suggesting that TNF binds to homogeneous TNF receptor sites. The number of receptor sites ranged between 770 and 2200 sites on TNF‐sensitive cells. The surface expression of these TNF receptors appeared to be necessary but not sufficient for the cells to become sensitive against the cytotoxic action of TNF. One of the HeLa clones was found to express the same number of TNF receptors as the most sensitive clone, but was nevertheless resistant to the toxic effect of TNF.