Regulation of Planar Cell Polarity by Smurf Ubiquitin Ligases

SummaryPlanar cell polarity (PCP) is critical for morphogenesis in metazoans. PCP in vertebrates regulates stereocilia alignment in neurosensory cells of the cochlea and closure of the neural tube through convergence and extension movements (CE). Noncanonical Wnt morphogens regulate PCP and CE in vertebrates, but the molecular mechanisms remain unclear. Smurfs are ubiquitin ligases that regulate signaling, cell polarity and motility through spatiotemporally restricted ubiquitination of diverse substrates. Here, we report an unexpected role for Smurfs in controlling PCP and CE. Mice mutant for Smurf1 and Smurf2 display PCP defects in the cochlea and CE defects that include a failure to close the neural tube. Further, we show that Smurfs engage in a noncanonical Wnt signaling pathway that targets the core PCP protein Prickle1 for ubiquitin-mediated degradation. Our work thus uncovers ubiquitin ligases in a mechanistic link between noncanonical Wnt signaling and PCP/CE

An experimentally derived confidence score for binary protein-protein interactions

Information on protein-protein interactions is of central importance for many areas of biomedical research. At present no method exists to systematically and experimentally assess the quality of individual interactions reported in interaction mapping experiments. To provide a standardized confidence-scoring method that can be applied to tens of thousands of protein interactions, we have developed an interaction tool kit consisting of four complementary, high-throughput protein interaction assays. We benchmarked these assays against positive and random reference sets consisting of well documented pairs of interacting human proteins and randomly chosen protein pairs, respectively. A logistic regression model was trained using the data from these reference sets to combine the assay outputs and calculate the probability that any newly identified interaction pair is a true biophysical interaction once it has been tested in the tool kit. This general approach will allow a systematic and empirical assignment of confidence scores to all individual protein-protein interactions in interactome networks