Judit M. Perez Ortiz

    
     E-mail:
perez211@umn.edu

     Year Entered: 2009

     Degrees Received:
     University of Puerto Rico, Rio Piedras
     Biology major
     B.S., 2009

     Thesis Advisor: Harry Orr, Ph.D.

     Thesis Research: AKAPs involved in the PKA pathway leading to
     abnormal phosphorylation of mutant Ataxin-1

     Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant
     trinucleotide-repeat neurodegenerative disorder. Typically manifesting in
     adulthood, it is characterized by a progressive loss of balance and
     coordination of movement. The mutant protein, Ataxin-1, aggregates in the nucleus and promotes cell death of Purkinje cells in the cerebellar cortex.

Our lab has shown that phosphorylation of Ataxin-1 at serine 776 is critical for disease (Emamian et al., 2004; Duvick et al., 2010) and further experiments suggest that the kinase involved in this phosphorylation is PKA, cAMP protein kinase. Additionally, recent experiments have shown that Ataxin-1 is heavily phosphorylated in Purkinje cells (Lagalwar, unpublished). What modulates PKA-mediated phosphorylation of Ser-776 in Ataxin-1 in Purkinje cells? While membrane receptors initiate signaling that leads to downstream activation of PKA, it is the A-kinase anchor proteins (AKAPs) that control the localization and stability of this signal.

The hypothesis being tested is that an AKAP is involved in the regulation of ataxin-1 phosphorylation by PKA in the cerebellar cortex. Two candidate AKAPs were selected for this study based on their abundance in the cerebellar cortex. The first, AKAP150, results in ataxic phenotype in a knockout mouse model (Tunquist et al., 2008). In addition to being an anchoring protein, the other candidate AKAP, Praja2, is a ubiquitin ligase that promotes persistent PKA activity (Lignitto et al., 2011). Considering that the loss of function of either AKAP disrupts downstream PKA signaling, it is conceivable that AKAP function is significant for PKA-dependent Ataxin-1 phosphorylation. As a first step towards characterizing whether either AKAP is involved in regulating ataxin-1 phosphorylation at Ser-776, I have been using a murine striatal cell line that express phosho-Ser776-ataxin-1. Using siRNA, shRNA, qPCR, and western blot techniques, the initial experimental paradigm consists of knocking down endogenous AKAP protein in this cell model and testing how it impacts Ataxin-1 phosphorylation.

Most of my time in this project has been spent troubleshooting the protocols to obtain reliable results, which are in progress. I am also in the process of rationally exploring other AKAPs that may be relevant in the regulation of Ataxin-1 phoshorylation to expand the list of candidate AKAPs and increase the likelihood of answering the hypothesis more accurately and promptly. Once a candidate AKAP is identified, the next step will be to use viral delivery to selectively knockdown AKAP in Purkinje cells in vivo in a SCA1 disease mouse model and examine Ataxin-1 phosphorylation and cerebellar pathology. Deciphering the role of AKAPs in SCA1/PKA signaling may contribute to understanding of SCA1 disease and provide a potential target for drug therapy.