Extension of the Drosophila lifespan by overexpression of a protein repair methyltransferase

Atypical protein isoaspartyl residues arise spontaneously during the aging process from the deamidation of protein asparaginyl residues and the isomerization of protein aspartyl residues. These abnormal residues are modified in cells by a strongly conserved protein carboxyl methyltransferase (PCMT) as a first step in a repair pathway. Because a decline in cellular repair mechanisms is hypothesized to contribute to senescence, we determined whether increased PCMT activity was correlated with enhanced longevity. Two ubiquitous promoters were used with the binary GAL4-UAS system to drive PCMT overexpression in Drosophila melanogaster. Flies expressing PCMT activity under the regulation of either the hsp70 or actin5C promoter had enzyme activities that were 3- or 7-fold higher, respectively, than control flies at 29 degreesC. Correlated with the observed increases in PCMT activities, such flies lived on average 32-39% longer than control flies. Lifespan extension was not observed at 25 degreesC with either hsp70- or actin5C-driven expression, indicating a temperature-dependent effect on longevity. We conclude that protein repair is an important factor in the determination of lifespan under certain environmental conditions. PCMT activity may become limiting under mild stress conditions that accelerate rates of protein damage.