Résumé
The Burkitt‐derived line, Daudi, whose proliferation is inhibited by human α‐interferon (IFN‐α), was treated with 125 I‐labelled recombinant human IFN‐αA. After separation from unbound ligand, cell‐bound IFN was extracted with the detergent digitonin yielding soluble and insoluble complexes of IFN and receptor, together with a certain amount of uncomplexed IFN. Soluble complexes were stable enough to be separated from uncomplexed IFN by permeation chromatography. Treatment of soluble complexes with the bifunctional reagent, disuccinimidyl suberate, yielded a radioactive product separating with an M r , of 130000 on electrophoresis in sodium dodecyl sulphate. Similar complexes could be recovered with sodium dodecyl sulphate from the digitonin‐insoluble residue, treated with the bi‐functional reagent. The total (soluble and insoluble) of complexed IFN obtained after digitonin extraction was a constant fraction (0.62) of the total cell‐bound radioactivity, being independent of the concentration of IFN added to the cells (> pM to > nM), and of the time of incubation (1 min to 20 h). However, between 30 min and 3 h of incubation, the insoluble complex increased, at the expense of the soluble complex, and there appeared a cellular pool of degraded ligand. From 3 h to 20 h the distribution of ligand‐derived radioactivity remained constant while the total amount decreased to less than 10% of its value at 30 min. This decrease in binding was matched by the appearance of an equivalent quantity of radiolabelled fragments in the culture medium. The inhibition of cellular division due to IFN was shown to be coincident with the disappearance of cellular binding and with the cell‐mediated degradation of receptor‐complexed IFN. We propose that IFN removes its own receptor and, in doing so, blocks a linked function necessary for the stimulated growth of Daudi cells.