Human Molecular Genetics Advance Access originally published online on October 17, 2008
Human Molecular Genetics 2009 18(1):164-177; doi:10.1093/hmg/ddn326
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Dissociation of tau toxicity and phosphorylation: role of GSK-3β, MARK and Cdk5 in a Drosophila model
1 Department of Neurology, Neurogenetics and Movement Disorders Programs, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095, USA 2 Institute of Biotechnology 3 Department of Life Science, National Tsing Hua University, Taiwan, Republic of China 4 Brain Research Institute 5 Center for Neurobehavioral Genetics, Semel Institute for Neuroscience and Human Behavior, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095, USA 6 Department of Neurology 7 Department of Neuroscience and Cell Biology 8 Department of Biochemistry and Molecular Biology 9 Mitchell Center for Neurodegenerative Diseases, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA
* To whom correspondence should be addressed at: University of Texas Medical Branch at Galveston, 10.138 Medical Research Building, 301 University Boulevard, Galveston, TX 77555, USA. Tel: +1 4097470009; Fax: +1 4097470015; Email: grjackso{at}utmb.edu
Received May 11, 2008; Accepted October 9, 2008
Hyperphosphorylation of tau at multiple sites has been implicated in the formation of neurofibrillary tangles in Alzheimer’s disease; however, the relationship between toxicity and phosphorylation of tau has not been clearly elucidated. Putative tau kinases that play a role in such phosphorylation events include the proline-directed kinases glycogen synthase kinase-3β (GSK-3β) and cyclin-dependent kinase 5 (Cdk5), as well as nonproline-directed kinases such as microtubule affinity-regulating kinase (MARK)/PAR-1; however, whether the cascade of events linking tau phosphorylation and neurodegeneration involves sequential action of kinases as opposed to parallel pathways is still a matter of controversy. Here, we employed a well-characterized Drosophila model of tauopathy to investigate the interdependence of tau kinases in regulating the phosphorylation and toxicity of tau in vivo. We found that tau mutants resistant to phosphorylation by MARK/PAR-1 were indeed less toxic than wild-type tau; however, this was not due to their resistance to phosphorylation by GSK-3β/Shaggy. On the contrary, a tau mutant resistant to phosphorylation by GSK-3β/Shaggy retained substantial toxicity and was found to have increased affinity for microtubules compared with wild-type tau. The fly homologs of Cdk5/p35 did not have major effects on tau toxicity or phosphorylation in this model. These data suggest that, in addition to tau phosphorylation, microtubule binding plays a crucial role in the regulation of tau toxicity when misexpressed. These data have important implications for the understanding and interpretation of animal models of tauopathy.