Internalization and degradation of human alpha-A interferon bound to bovine MDBK cells: regulation of the decay and resynthesis of receptors.

The binding of 125I-labeled human interferon alpha-A (HuIFN-alpha A) to receptors of bovine MDBK cells was investigated. About 4-fold more 125I-interferon was bound at 37 degrees C than at 0 degrees C. To establish whether the cell-bound IFN was internalized, the cells were treated with diluted acetic acid, a procedure known to remove polypeptides bound to the cell surface. About 80% of the IFN bound at 0 degrees C was dissociated from the cells by this treatment, whereas only 45% of that bound after a 2 h incubation at 37 degrees C was dissociated. Release of cell-bound 125I-interferon by cells washed and incubated in fresh medium was next examined at the two temperatures. At 0 degrees C, up to 50% of cell-bound IFN was released into the medium over a 2 h period, whereas at 37 degrees C the cell-bound radioactivity was slowly released over several hours as acid-soluble degradation products. Interferon was therefore internalized and degraded by MDBK cells incubated at 37 degrees C, but not by cells incubated at 0 degrees C. The increased binding at 37 degrees C could possibly be explained by the internalization of IFN/receptor complexes and by the recycling of the receptors to the cell surface. This recycling was limited, however, since incubation of MDBK cells with unlabeled IFN led to a rapid decrease or down regulation of available receptors. Recovery of binding activity was prevented by the addition of inhibitors of protein and RNA synthesis, suggesting that de novo synthesis of receptors was required. The half-life of the IFN receptor in the presence of cycloheximide was about 3 h.(ABSTRACT TRUNCATED AT 250 WORDS)