Inhibition of polypeptide chain initiation in Daudi cells by interferons. Evidence that activity of initiation factor eIF-2 and availability of mRNA are unimpaired

Abstract

The accompanying paper [McNurlan & Clemens (1986) Biochem. J. 237, 871-876] shows that the inhibition of proliferation of Daudi cells by human interferons is associated with impairment of the overall rate of protein synthesis. We have examined whether two of the mechanisms which are believed to control translation in interferon-treated virus-infected cells may be responsible for the inhibition of protein synthesis during the antiproliferative response in these uninfected cells. Although the rate of polypeptide chain initiation is lower in interferon-treated Daudi cells, as indicated by the disaggregation of polysomes, there is no significant inhibition of activity of initiation factor eIF-2 or of [40 S . Met-tRNAf] initiation complex formation in cell extracts. The phosphorylation state of the alpha subunit of eIF-2 remains unaltered. There is no major decrease in mRNA content as a proportion of total RNA up to 4 days of interferon treatment, as judged by poly(A) content, although the amount of total mRNA/10(6) cells eventually declines. The mRNA present in extracts from interferon-treated cells remains translatable when added to an mRNA-dependent reticulocyte lysate system. We conclude that neither the interferon-inducible eIF-2 protein kinase pathway nor the 2',5'-oligo(adenylate)-ribonuclease L pathway are responsible for the inhibition of polypeptide chain initiation. Rather, the data suggest impairment at the level of formation of [80 S ribosome X mRNA] initiation complexes.