Background Huntington9s disease (HD) is an inherited neurodegenerative disorder characterised by the accumulation of N-terminal polyglutamine (polyQ)-containing mutant huntingtin (mHtt) fragments in affected neurons. Several lines of evidence indicate that the process of mHtt misfolding and aggregation is associated with cytotoxicity in HD. Aims The identification and characterisation of proteins that can modulate this process is critical for understanding HD pathogenesis and the development of novel therapies. The collapsin response mediator protein (CRMP) family mediates many aspects of neuronal development and plasticity by regulating cytoskeleton dynamics. Here, we studied the interaction of CRMP4 with mHtt. Methods and Results We found that CRMP4 protein levels are strongly reduced in a cell model of HD. By using cell-free and cell-based assays, we demonstrated that CRMP4 reduces polyQ-mediated mHtt aggregation and cytotoxicity. Moreover, we observed that CRMP4 undergoes proteolytic processing by calpain I under toxic mHtt conditions. The truncated CRMP4ΔC499 variant directly interacted with mHtt, and is known to trigger apoptosis. Conclusion Our results suggest a novel role for CRMP4 in HD pathogenesis. Funding Funded by NGFN Plus (BMBF).

The yeast two-hybrid (Y2H) system is the most widely applied methodology for systematic protein–protein interaction (PPI) screening and the generation of comprehensive interaction networks. We developed a novel Y2H interaction screening procedure using DNA microarrays for high-throughput quantitative PPI detection. Applying a global pooling and selection scheme to a large collection of human open reading frames, proof-of-principle Y2H interaction screens were performed for the human neurodegenerative disease proteins huntingtin and ataxin-1. Using systematic controls for unspecific Y2H results and quantitative benchmarking, we identified and scored a large number of known and novel partner proteins for both huntingtin and ataxin-1. Moreover, we show that this parallelized screening procedure and the global inspection of Y2H interaction data are uniquely suited to define specific PPI patterns and their alteration by disease-causing mutations in huntingtin and ataxin-1. This approach takes advantage of the specificity and flexibility of DNA microarrays and of the existence of solid-related statistical methods for the analysis of DNA microarray data, and allows a quantitative approach toward interaction screens in human and in model organisms.

Effective prediction of the direction of signal flow in an interaction network enables modeling of signaling dynamics and identification of regulatory proteins.