Identification of ATF-7 and the insulin signaling pathway in the regulation of metallothionein in C. elegans suggests roles in aging and reactive oxygen species

It has been proposed that aging results from the lifelong accumulation of intracellular damage via reactions with reactive oxygen species (ROS). Metallothioneins are conserved cysteine- rich proteins that function as efficient ROS scavengers and may affect longevity. To better understand mechanisms controlling metallothionein expression, the regulatory factors and pathways that controlled cadmium-inducible transcription of the C. elegans metallothionein gene, mtl-1, were identified. The transcription factor ATF-7 was identified in both ethylmethanesulfonate mutagenesis and candidate gene screens. PMK-1 and members of the insulin signaling pathway, PDK-1 and AKT-1/2, were also identified as mtl-1 regulators. Genetic and previous results support a model for the regulation of cadmium-inducible mtl-1 transcription based on the derepression of the constitutively active transcription factor ELT2. In addition, knockdown of the mammalian homologs of PDK1 and ATF7 in HEK293 cells resulted in changes in metallothionein expression, suggesting that this pathway was evolutionarily conserved. The insulin signaling pathway is known to influence the aging process; however, various factors responsible for affecting the aging phenotype are unknown. Identification of portions of the insulin signaling pathway as regulators of metallothionein expression supports the hypothesis that longevity is affected by the expression of this efficient ROS scavenger.