Interaction of the ubiquitin carboxyl terminal esterase L1 with α2-adrenergic receptors inhibits agonist-mediated p44/42 MAP kinase activation

Neuroprotective effects of α2-adrenergic receptor (AR) agonists are mediated via the α2AAR subtype, but the molecular mechanisms underlying these actions are still not elucidated. A two-hybrid screen was performed to identify new proteins that may control α2AR receptor function and trafficking. This screen identified the ubiquitin carboxyl-terminal hydrolase-L1 (Uch-L1), a protein associated with Parkinson's disease, as α2AR interacting protein. This interaction was confirmed and evaluated by GST pull down assays demonstrating that Uch-L1 binds preferentially to the α2AAR subtype and only with less affinity to α2BAR and α2CAR. Co-immunoprecipitation of epitope-tagged proteins confirmed the specificity of this interaction in vivo. Moreover, co-transfection of a truncated G-protein coupled receptor kinase-DNA preventing α2AR phosphorylation led to an increased signal-strength of coimmunoprecipitated Uch-L1. Confocal laser microscopy showed that interaction of α2AAR and Uch-L1 occurred in the cytoplasm. α2AR agonist mediated activation of p44/42 MAP Kinase was drastically decreased in the presence of Uch-L1 indicating a functional relevance of this interaction. These findings may present a mechanism contributing to subtype-specific α2AR trafficking and a potential pathway for the neuroprotective effects of α2AR agonists.