Hsp90 Enhances Degradation of Oxidized Calmodulin by the 20 S Proteasome

Abstract

The 20 S proteasome has been suggested to play a critical role in mediating the degradation of abnormal proteins under conditions of oxidative stress and has been found in tight association with the molecular chaperone Hsp90. To elucidate the role of Hsp90 in promoting the degradation of oxidized calmodulin (CaM ox ), we have purified red blood cell 20 S proteasomes free of Hsp90 and assessed their ability to degrade CaM ox in the absence or presence of Hsp90. Purified 20 S proteasome does not degrade CaM ox unless Hsp90 is added. CaM ox degradation is sensitive to both proteasome and Hsp90-specific inhibitors and is further enhanced in the presence of 2 mM ATP. Irrespective of the presence of Hsp90, we find that unoxidized CaM is not significantly degraded. Direct binding measurements demonstrate that Hsp90 selectively associates with CaM ox ; essentially no binding is observed between Hsp90 and unoxidized CaM. These results indicate that Hsp90 in association with the 20 S proteasome can selectively associate with oxidized and partially unfolded CaM to promote degradation by the proteasome.

Oxidative Stress-Mediated Regulation of Proteasome Complexes

“…Interestingly, under non-stressed conditions Hsp90 and ␣-crystalline inhibit 20S proteasome activity (108,110,111), but upon oxidative stress, these chaperones protect activated 20S proteasomes from oxidative inactivation (106 -108). Hsp90 also appears to selectively promote the degradation of oxidized substrates by the 20S proteasome in vitro (112). Taken together, these results suggest that molecular chaperones may play a role in regulating proteasome activity in response to oxidative stress by both stabilizing specific proteolytic activities and by aiding the recognition and degradation of oxidized substrates.…”

Protein Oxidation in Aging: Does It Play a Role in Aging Progression?

“…For example, Conconi et al showed that Hsp90 leads to an enhanced activity of the 20 proteasome after FeCl 3 -induced ROS formation in vitro (25). Whittier et al showed that Hsp90 is selectively involved in 20S proteasome-related degradation of oxidized calmodulin, but not in degradation of native calmodulin (159). In addition, a direct participation of HSPs (Hsp70 and Hsp90) in the degradation by the 26S proteasome is postulated (Fig.…”

Age-dependent inhibition of proteasome chymotrypsin-like activity in the retina

“…Recent evidence has shown that the presence of HSP90 is essential for the degradation of oxidized protein substrates by the 20S proteasome (Whittier et al, 2004). To determine if lower HSP90 content could help explain the slower degradation of HNE-modified casein, we measured HSP90 content by Western immunoblotting.…”