The manganese superoxide dismutase Ala16Val dimorphism modulates both mitochondrial import and mRNA stability

Abstract

A genetic dimorphism incorporates either alanine (Ala) or valine (Val) in the mitochondrial targeting sequence (MTS) of manganese superoxide dismutase (MnSOD). The Ala-MTS confers a 40% higher MnSOD activity than the Val-MTS after import into isolated mitochondria in vitro. The present study aimed to characterize functional consequences in whole cells. HuH7 human hepatoma cells were transfected with vectors encoding for the human Ala- or Val-MnSOD variants fused to a Myc-His-tag. The Ala-variant resulted in four-fold higher levels of the mature exogenous protein and MnSOD activity than the Val-variant. Studies with a proteasome inhibitor indicated that precursor proteins are either imported into the mitochondria or degraded by the proteasome. Despite identical levels 8 h after transfection, mRNA levels at 36 h were two-fold higher for the Ala-encoding mRNA than the Val-mRNA. Decreasing the mitochondrial membrane potential decreased both MnSOD mitochondrial import and its mRNA levels. Much larger differences in the activity of the human Val- and Ala-MnSOD variants are observed in whole cells rather than after import experiments performed in vitro. First, the slowly imported Val-MnSOD is degraded by the proteasome in cells. Second, the slower mitochondrial import of the Val-variant may be associated with decreased mRNA stability, possibly due to impaired cotranslational import.

Functional Variant of Manganese Superoxide Dismutase (SOD2 V16A) Polymorphism Is Associated with Prostate Cancer Risk in the Prostate, Lung, Colorectal, and Ovarian Cancer Study

“…The Ala variant of SOD2 allows more efficient SOD2 import into the mitochondrial matrix and generates more active SOD2 compared with the Val variant (14)(15)(16). Thus, it is hypothesized that the higher activity (Ala) variant suppresses prostate carcinogenesis; however, our results and previous association studies on prostate cancer contradict this hypothesis (17,18).…”

“…The Ala variant at a mitochondrial targeting sequence of SOD2 allows more efficient SOD2 uptake into the mitochondrial matrix and generates more active SOD2 compared with the Val variant, suggesting that Ala/Ala homozygous subjects may have higher SOD2 activity (14)(15)(16). Contrary to this, two small epidemiologic studies on the association between SOD2 polymorphism and prostate cancer showed the Ala variant associated with increased risk of prostate cancer in poorly differentiated prostate cancer cases (17) or men with lower antioxidant intakes (18).…”

Protective effect of myricetin in dextran sulphate sodium-induced murine ulcerative colitis

“…MPO and NO are known sources of free radicals and are able to induce the reduction of ferritin (Fe 3+ ) to free Fe 2+ , contributing to oxidative damage (21,22). Moreover, increased MDA activity leads to lipid peroxidation, which causes the cross-linking of protein and nucleic acid molecules and cell toxicity.…”

Mitochondrial dysfunction and oxidative stress in the pathogenesis of alcohol- and obesity-induced fatty liver diseases

“…The alanine-SOD2 variant, whose pre-sequence is an α-helix, is readily imported and achieves high activity in mitochondria, whereas the valine-SOD2 variant, whose pre-sequence is a partial β-sheet, is poorly imported resulting in low SOD2 activity [127,128]. It is proposed that the presence of the high-activity, alanine-SOD2 variant will increase hydrogen peroxide production in mitochondria, which might have the effect to disrupt cellular redox signaling pathways and initiate oxidative damage [129].…”