OP2 - HSP90 impairment through oxidative cleavage leads to oxidized proteins accumulation

Abstract

Oxidative stress (OS), has been associated to a variety of phenomena as cancer progression, neurodegeneration, obesity and ageing itself. At the molecular level, OS leads to protein carbonylation, a non-enzymatic irreversible event and common feature of aged cells. Carbonylated proteins are dysfunctional and can accumulate in the form of insoluble protein aggregates that alter cellular functioning. To cope with carbonylated proteins, cells employ the proteasome, the main non-lysosomal structure for carbonylated proteins turnover. However, if the degrading rate is inferior to carbonylated proteins formation rate, protein aggregates form. In a previous study, in oxidative stress challenged cells we could verify that cytoplasmatic actin becomes heavily carbonylated and forms oxidized actin aggregates, which lead to proliferation impairment and proteasome activity diminishment, similar to senescence like states. Because under these oxidative conditions there is a proteostasis disturbance, such as oxidized proteins (especially actin) accumulation and proteasome activity impairment, Hsp90 involvement was studied. Hsp90, a molecular chaperone, assists oxidized proteins degradation and also protects the 20S proteasome from oxidative inactivation. We reasoned that the mechanism by which protein aggregates form, is mainly due to Hsp90 lesser functionality, which we attribute to cleavage. In our study, we verified cleaved Hsp90 in protein aggregates and that its fragmentation occurred before actin insolubilization. Adding to this, when Hsp90 cleavage was prevented employing a drug, no protein aggregates were found. Furthermore, preliminary results show that under stress, cells overexpressing cleaved Hsp90 exhibited an increase, comparing to non-transfected or full Hsp90 overexpressing cells, in carbonylated proteins levels content. We are convinced, that Hsp90 cleavage is an important event for oxidized protein accumulation and proteasome inactivation. However, further studies should follow to confirm our hypothesis.