ATP- and ATP+ ubiquitin-stimulated proteolysis in rat liver and Yoshida ascites hepatoma

Calorie restriction, stress and the ubiquitin-dependent pathway in mouse livers

Calorie restriction (R) is the only known method to delay the aging process and extend mean and maximal lifespan in rodents. R has been shown to delay the age-related accumulation of damaged proteins and to protect organisms from various stresses which can produce damaged proteins. Such stresses include irradiation, heat shock, and oxidative stress. The ubiquitin- and ATP-dependent proteolytic pathway (UPP) has been associated with the degradation of abnormal and/or damaged proteins. We examined the effect of diet and oxidative stress on activities of the UPP in supernatants from livers taken from 23-month-old Emory mice which had been exposed to an in-vivo injection of paraquat. Paraquat induces oxidative stress by generating superoxide radicals. In livers from non-stressed animals, steady-state levels of endogenous ubiquitin conjugates, de novo conjugate formation, and E1 and E2 activities were significantly lower in R animals than in control (C) animals. However, after exposure to paraquat, levels of endogenous ubiquitin conjugates were significantly higher in R versus C animals, and de novo conjugate formation and E1 and E2 activities in R animals rose to levels which were indistinguishable from levels of these activities noted in C animals. R was associated with an increased ability to degrade beta-lactoglobulin by the UPP after an oxidative stress was imposed. Ability to degrade beta-lactoglobulin by the C or R livers in non-stressed animals was not significantly different. Taken together, these data indicate that oxidative stress in R animals is associated with enhanced levels of ubiquitin conjugates and that this enhancement may be due to an increase in UPP activity. These data also indicate that the ability to form ubiquitin conjugates and the UPP system does not change with oxidative stress in C animals. The latter is consistent with prior reports that suggests that older C animals may already be in a state of enhanced oxidative stress and that activities of the UPP provide a sensitive indicator of levels of cellular redox status.

Aging, calorie restriction and ubiquitin-dependent proteolysis in the livers of Emory mice

Calorie restriction (R), the only known method to delay the aging process and extend mean and maximal lifespan, has been shown to delay the age-related decline in protein degradation. There are several proteolytic pathways. The ubiquitin- and ATP-dependent proteolytic pathway (UPP) is frequently associated with degradation of damaged abnormal and/or regulatory proteins. We examined the effect of aging and R on supernatants of livers taken from young (4.5 months) and old (23 months) Emory mice. Aging was associated with increased levels of endogenous ubiquitin conjugates, enhanced ability to form high molecular weight conjugates and ubiquitin activating (E1) and ubiquitin conjugating (E2) activity in the control (C) liver supernatants. The age-related increase in levels of endogenous ubiquitin conjugates in liver appears to be primarily due to increased E1 and E2 activities. R prevented the age-related increase in E1 and E2 activity, and thus prevented the age-related increase in levels of ubiquitin conjugates. In spite of the age-related increase in ubiquitin conjugates, no age-related changes in ubiquitin-dependent proteolytic pathway were observed in the C animals. R was associated with an enhanced ability (130%) to degrade beta-lactoglobulin by the ubiquitin-dependent proteolytic pathway in livers from 4.5-month-old animals relative to age-matched C livers. However, rates of the ubiquitin-dependent degradation of beta-lactoglobulin in the 23-month-old C and R animals were indistinguishable. There were no age- or diet-related differences in the ability to degrade another substrate, oxidized ribonuclease (RNase).