ANISOMYCIN AND RAPAMYCIN DEFINE AN AREA UPSTREAM OF P70 85(S6K) CONTAINING A BIFURCATION TO HISTONE H3-HMG-LIKE PROTEIN-PHOSPHORYLATION ANDC-FOS C-JUN INDUCTION/

Anisomycin, a translational inhibitor, synergizes with growth factors and phorbol esters to superinduce c-fos and c-jun by a number mechanis ms, one of which is its ability to act as a potent signalling agonist, producing strong, prolonged activation of the same nuclear responses as epidermal growth factor or tetradecanoyl phorbol acetate. These res ponses include the phosphorylation of pp33, which exists in complexed and chromatin-associated forms, and of histone H3 and an HMG-like prot ein. By peptide mapping and microsequencing, we show here that pp33 is the phosphoprotein S6, present in ribosomes and in preribosomes in th e nucleolus. Ablation of epidermal growth factor-, tetradecanoyl phorb ol acetate-, or anisomycin-stimulated S6 phosphorylation by using the p70/85(S6k) inhibitor rapamycin has no effect on histone H3 and HMG-li ke protein phosphorylation or on the induction and superinduction of c -fos and c-jun. Further, [S-35]methionine-labelling and immunoprecipit ation studies show that the ablation of S6 phosphorylation has no disc ernible effect on translation in general or translation of newly induc ed c-fos transcripts. Finally, we show that anisomycin augments and pr olongs S6 phosphorylation not by blocking S6 phosphatases but by susta ined activation of p70/85(S6k). These results suggest the possible use of anisomycin and rapamycin to define upstream and downstream boundar ies of an area of signalling above p70/85(S6k) which contains a bifurc ation that produced histone H3-HMG-like protein phosphorylation and c- fos-c-jun induction in the nucleus.