Phosphorylation of ATXN1 at Ser776 in the cerebellum

Abstract

Spinocerebellar ataxia type 1 (SCA1) is one of nine inherited neurodegenerative disorders caused by a mutant protein with an expanded polyglutamine tract. Phosphorylation of ataxin‐1 (ATXN1) at serine 776 is implicated in SCA1 pathogenesis. Previous studies, utilizing transfected cell lines and a Drosophila photoreceptor model of SCA1, suggest that phosphorylating ATXN1 at S776 renders it less susceptible to degradation. This work also indicated that oncogene from AKR mouse thymoma (Akt) promotes the phosphorylation of ATXN1 at S776 and severity of neurodegeneration. Here, we examined the phosphorylation of ATXN1 at S776 in cerebellar Purkinje cells, a prominent site of pathology in SCA1. We found that while phosphorylation of S776 is associated with a stabilization of ATXN1 in Purkinje cells, inhibition of Akt either in vivo or in a cerebellar extract‐based phosphorylation assay did not decrease the phosphorylation of ATXN1‐S776. In contrast, immunodepletion and inhibition of cyclic AMP‐dependent protein kinase decreased phosphorylation of ATXN1‐S776. These results argue against Akt as the in vivo kinase that phosphorylates S776 of ATXN1 and suggest that cyclic AMP‐dependent protein kinase is the active ATXN1‐S776 kinase in the cerebellum.

14-3-3 Proteins and Spinocerebellar Ataxia Type 1: from Molecular Interaction to Human Neuropathology

“…1f). Recently, Jorgenson et al [34] reported that Akt is not the cerebellar ataxin-1-S776 kinase and proposed the cyclic AMP-dependent protein kinase as a candidate S776 kinase. However, it is still unclear which kinase is the "human" cerebellar ataxin-1-S776 kinase, and which isoform of 14-3-3 proteins is most effective in and responsible for stabilization of the phosphorylation of the "human" cerebellar ataxin-1-S776.…”

RAS–MAPK–MSK1 pathway modulates ataxin 1 protein levels and toxicity in SCA1

“…Building on our previous discovery that ATXN1 levels are highly sensitive to phosphorylation at residue S776 (mutation of serine to alanine decreases both ATXN1 stability and toxicity) 20,29 , we investigated whether the MAPK pathway kinases (MEK, ERK and MSK1) recovered in our screens phosphorylate ATXN1 at S776. This residue falls within the consensus phosphorylation sequence RXXS that is conserved in ATXN1 homologues (Fig.…”

Prediction and Experimental Detection of Structural and Functional Motifs in Intrinsically Unfolded Proteins

“…Further to polyQ expansion and nuclear localization, phosphorylation of S776 has been identified as a condition necessary for development of SCA1 (Emamian et al, 2003). Phosphorylation of S776 has been confirmed to occur in vivo (Emamian et al, 2003;Jorgensen et al, 2009) and is required for recognition of ataxin-1 by the protein 14-3-3, a molecular adaptor which modulates, in a phosphorylation-dependent manner, the function of different proteins in their specific context (Chen et al, 2003). Mutation of S776 to an alanine in expanded ataxin-1, despite not affecting nuclear localization, prevented the development of the SCA1 phenotype (Emamian et al, 2003).…”

“…Among all the predicted phosphorylation sites only the ones which have been confirmed in vivo and are supportive of the prediction of other phosphopeptide motifs have been included. a Phosphorylation site and kinase experimentally confirmed in cerebellum (Jorgensen et al, 2009). b Phosphorylation site confirmed, kinase not identified (Dephoure et al, 2008;Vierra-Green et al, 2005) putative phosphorylation-dependent protein-protein interaction motifs are predicted in the N-terminus of ataxin-1.…”

“…In the following sections we shall discuss a detailed analysis of the ataxin-1 primary sequence and how this study has suggested working hypotheses which could then be tested experimentally using structural and cellular approaches. We discuss the identification of two major potential IURs in ataxin-1 which contain short linear motifs important for phosphorylation, aggregation and protein-protein interactions that are directly related to pathogenesis (Chen et al, 2003;de Chiara et al, 2009;Emamian et al, 2003;Jorgensen et al, 2009;Klement et al, 1998). We pay particular attention to the prediction and characterization of the structural and functional features of the different protein regions and to the identification of key ELMs of crucial importance both for the normal and anomalous behaviour of the protein.…”