Huntingtin N17 Domain is a Reactive Oxygen Species Sensor Regulating Huntingtin Phosphorylation and Localization

Abstract

The huntingtin N17 domain is the master regulator of huntingtin intracellular localization. N17 is post-translationally modified, and phosphorylation of N17 serines 13 and 16 facilitate the stress dependent nuclear translocation of huntingtin by inhibiting CRM1 binding and nuclear export. In Huntington’s disease (HD), mutant huntingtin is hypo-phosphorylated and increasing N17 phosphorylation has been shown to be protective in HD mouse models. N17 phosphorylation is therefore a valid therapeutic sub-target of huntingtin. The ER stresses that have been previously characterized to affect huntingtin phosphorylation are broad, likely activating a plethora of response pathways. Thus, in this study, we sought to define a specific stress that could affect huntingtin phosphorylation and nuclear localization. Here we show that huntingtin localization and phosphorylation can be specifically affected by reactive oxygen species (ROS). We identify a highly conserved methionine at position 8 (M8) as the specific sensor of oxidative species within N17 and show the capacity of oxido-mimetic M8 point mutations to affect N17 structure, localization and phosphorylation. We also define a specific molecular mechanism whereby N17 oxidation promotes membrane dissociation, thus increasing kinase accessibility and subsequent phosphorylation. These results define a precise molecular mechanism for the normal biological regulation of huntingtin phosphorylation by oxidative signalling. This ability of huntingtin to sense ROS levels at the ER provides a link between age-associated stress and altered huntingtin function. It suggests that ROS stress due to aging may be a critical molecular trigger of HD that could explain the age-onset nature of disease.