Control of mRNA decay by heat shock ubiquitin proteasome pathway

Cytokine and proto-oncogene messenger RNAs (mRNAs) are rapidly degraded thr ough AU-rich elements in the 3' untranslated region. Rapid decay involves A U-rich binding protein AUF1, which complexes with heat shock proteins hsc70 -hsp70, translation initiation factor elF4G, and poly(A) binding protein. A U-rich mRNA decay is associated with displacement of elF4G from AUF1, ubiqu itination of AUF1, and 'degradation of AUF1 by proteasomes. Induction of hs p70 by heat shock, down-regulation of the ubiquitin-proteasome network, or inactivation of ubiquitinating enzyme E1 all result in hsp70 sequestration of AUF1 in the perinucleus-nucleus, and all three processes block decay of AU-rich mRNAs and AUF1 protein. These results link the rapid degradation of cytokine mRNAs to the ubiquitin-proteasome pathway.