A new function in the nuclear compartment

Background. Recent evidences showed that, in PBMCs from sALS patients, there is an over-expression of SOD1 mRNA (Gagliardi et al. 2010), which is in contrast with the unchanged cytoplasmic level of the protein (Cova et al., 2006). This discrepancy could be explained considering a re-localization of the “missing” protein in the nucleus. Moreover, in PBMCs of sALS patients, SOD1 translocates from the cytoplasm to the nuclear compartment (Cereda et al., 2013). Together with this, Tsang and colleagues suggested that in yeast SOD1 has a new function in controlling the oxidative stress response (Tsang et al., 2014). Aim. The exact role of SOD1 in the nuclear compartment remains a critical issue to clarify. Thus, we aim to investigate whether and how nuclear SOD1 could act against oxidative stress both in neuroblastoma cell line SHSY5Y, a cellular model of ALS, and in PBMCs of sALS patients. Results. First, we confirmed that under oxidative stress SOD1 re-locates into the nucleus; SOD1 levels decreases after 30 min of 1mM H2O2 treatment, and rescues at T60; probably as a consequence of new protein synthesis. Mass spectrometry (MS) data highlight that SOD1 nuclear re-localization is prompted by phosphorylation of both serine and threonine at T60. Moreover, Chk2 seems to play a critical role in the regulation of SOD1 localization. Comet assay revealed that SOD1-NLS cells showed no comets, indicating that, when SOD1 is located into the nucleus, minor or none DNA fragmentation occurred. Finally, an increase in histone H3 acetylation at both T30 and T60, suggested us a possible role of nuclear SOD1 in gene transcription. Conclusion. In response to oxidative stress, we demonstrated that SOD1 re-locates at nuclear level, where it plays new functions. We reported an involvement of nuclear SOD1 in order to provide resistance against oxidative DNA damage, and a role in the regulation of gene transcription.