Redox regulation of the proteasome in T lymphocytes during aging

Proteasome is a major cellular organelle responsible for the regulated turnover of both normal and misfolded proteins. Recent reports from our laboratory have implicated lowered proteasomal chymotryptic activity to be responsible for decreased induction of the transcription factor NFkappaB in T lymphocytes during aging. In this study, we have further analyzed the basis for this decline in proteasomal function, by focusing on the role of oxidative stress. On exposure to the prooxidant BSO, both ATP-stimulatable 26S and ATP-independent 20S proteasomal catalytic activity could be down-regulated in T cells from young donors, mimicking the decline observed in T cells from the elderly. Loss in these catalytic activities, following exposure to prooxidant stimulus, also resulted in a decline in both activation-induced proliferation and degradation of the inhibitor IkappaBalpha, with concomitant increase in the accumulation of carbonylated proteins, mimicking responses seen in T cells from the elderly. Pretreatment with an antioxidant, NAC, could override prooxidant-mediated, but not age-associated, decrease in both 20S and 26S proteasomal activities. These results suggest that the decrease in proteasomal activities observed during aging may be secondary to oxidative stress and underlie immune senescence.