Proteasome-dependent degradation of cytosolic chaperonin CCT

The chaperonin containing t-complex polypeptide 1 (CCT) is a heterooligomer ic molecular chaperone that assists in the folding of actin, tubulin, and o ther cytosolic proteins. We show here that degradation of CCT in mammalian cells is inhibited by a proteasome-specific inhibitor, lactacystin. When CC T synthesis was inhibited by growth arrest of cells, the decrease in CCT le vels was much slower in the presence of lactacystin than in its absence. Pu lse-chase experiments indicated that degradation of CCT is inhibited 2- to 2.5-fold by addition of lactacystin. In addition, CCT degradation rate in t s85 cells that produce thermolabile ubiquitin-activating enzyme E1 was redu ced 3-fold at the nonpermissive temperature compared to the degradation at the permissive temperature. These results indicate that the ubiquitin-prote asome system is involved in CCT degradation. (C) 2000 Academic Press.