STRESS-ACTIVATED KINASES REGULATE PROTEIN STABILITY

Proteasome inhibitors have been used to demonstrate that many proteins of the signal transduction pathways are regulated by degradation via the ubiquitin-proteasome pathway. The key question is what events targ et specific proteins for ubiquitination at one time and prevent ubiqui tination at other times? In this review, we develop the notion that th ere is a direct relationship between the phosphorylation/dephosphoryla tion cascade of the signal transduction pathways and the targeting of the regulatory proteins for ubiquitination. We present examples where phosphorylation appears to alter the interaction between the targeting systems and the substrate by modifying the targeting system, the subs trate, or both. These interacting systems are seen in the response of p53, c-jun and ATF-2 in cells subjected to stress or DNA damage and to the normal regulated response in a variety of pathways including the I kappa B-NF kappa B and JAK-STAT pathways, The interweaving of the tw o post-translational networks, phosphorylation and ubiquitination, pro vides a powerful insight into global regulatory control pathways.