Abstract 
Ion transport regulation in mammals is important because dysfunctions in this process may produce cardiovascular and neurodegenerative diseases. Mutations in the gene encoding the AMP-activated protein kinase (AMPK) have been associated with cardiovascular and neurodegenerative diseases, such as Wolf Parkinson White syndrome, which causes arrhythmias, and a type of progressive myoclonic epilepsy called Lafora Disease. The dysfunction of ion transporters is involved in the physiopathology of these diseases. Post-translational regulation controls membrane proteins strictly and dynamically in response to specific stimuli. Both ubiquitylation and phosphorylation are studied in this Thesis as examples of post-translational regulation. The phosphorylation of membrane proteins may regulate their activity either positively or negatively, while the ubiquitylation controls degradation and recycling that may occur after endocytosis, thereby determining the amount of each membrane transporter present at the plasma membrane. 
The starting point of this Thesis is the model which consists of AMPK as a sodium channel (ENaC) regulator via the phosphorylation of the E3 ubiquitin ligase Nedd4-2, a direct regulator of the channel. The interaction between AMPK and Nedd4-2 is characterized and its role in the interaction between Nedd4-2 and ENaC is studied. The model indicates that activated AMPK phosphorylates Nedd4-2, which favors its interaction with ENaC and therefore its ubiquitylation, reducing its presence in the membrane. During this work, we determined that the physical interaction between AMPK and Nedd4-2 is likely to be transient or indirect. However, we find that both are regulated in a reciprocal manner: Nedd4-2 ubiquitinates AMPK and AMPK phosphorylates Nedd4-2 on at least three serine residues. We show that one of these phosphorylation sites has a role in the in vitro interaction between Nedd4-2 and ENaC when AMPK is present and active. Although more experimental approaches are needed to define the physiological relevance of these post-translational modifications, this study adds a novel component and contributes to the molecular characterization of the regulation of the E3 ubiquitin ligase Nedd4-2 by the protein kinase AMPK