Sci. myotubularin interactome comprises 66 high confidence (false discovery rate 1%) interactions, including 18 pairwise interactions between individual myotubularins. The results reveal a number of potential signaling contexts for this family of enzymes, including an intriguing, novel role for myotubularin-related protein 3 and myotubularin-related protein 4 in the regulation LOXL2-IN-1 HCl of abscission, Rabbit polyclonal to ALOXE3 the final step of mitosis in which the membrane bridge remaining between two daughter cells is usually cleaved. Both depletion and overexpression of either myotubularin-related protein 3 or myotubularin-related protein 4 result in abnormal midbody morphology and cytokinesis failure. Interestingly, myotubularin-related protein 3 and myotubularin-related protein 4 do not exert their effects through lipid regulation at the midbody, but regulate abscission during early mitosis, by interacting with the mitotic kinase polo-like kinase 1, and with centrosomal protein of 55 kDa (CEP55), an important regulator of abscission. Structure-function analysis reveals that, consistent with known intramyotubularin interactions, myotubularin-related protein 3 and myotubularin-related protein 4 interact through their respective coiled coil domains. The conversation between myotubularin-related protein 3 and polo-like kinase 1 relies on the divergent, nonlipid binding Fab1, YOTB, Vac1, and EEA1 domain name of myotubularin-related protein 3, and myotubularin-related protein 4 interacts with CEP55 through a short GPPXXXY motif, analogous to endosomal sorting complex required for transport-I components. Disruption of any of these interactions results in abscission failure, by disrupting the proper recruitment of CEP55, and subsequently, of endosomal sorting complex required for transport-I, to the midbody. Our data suggest that myotubularin-related protein 3 and myotubularin-related protein 4 may act as a bridge between CEP55 and polo-like kinase 1, ensuring proper CEP55 phosphorylation and regulating CEP55 recruitment to the midbody. This LOXL2-IN-1 HCl work provides a novel role for myotubularin-related protein 3/4 heterodimers, and highlights the temporal and spatial complexity of the regulation of cytokinesis. The myotubularins are a subfamily of protein tyrosine phosphatases (PTPs)1, consisting of sixteen conserved proteins. Despite made up of the conserved C(X)5R catalytic motif found in all protein tyrosine phosphatases, myotubularins harbor active sites that do not dephosphorylate tyrosine, but instead catalyze the conversion of the phosphatidylinositol-type lipids phosphatylinositol 3 phosphate (PI3P) and phosphatylinositol 3,5 phosphate (PI3,5P) to phosphatidylinositol (PI) and phosphatylinositol 5 phosphate (PI5P), respectively (1). Phosphatidylinositols are important molecules in a variety of processes, and as enzymatic regulators, myotubularins may function in cell proliferation, differentiation, survival, and cytoskeletal and junctional dynamics (1, 2). Of the sixteen myotubularins, only nine LOXL2-IN-1 HCl are active enzymes (supplemental Fig. S1 0.05, ** 0.01, and *** 0.001. In all box-whisker plots in Fig. 6, the red horizontal line denotes the mean, the pink box represents the 95% confidence interval, and the grayed region represents one standard deviation of the data. Open in a separate window Fig. 6. MTMR3 and MTMR4 regulate CEP55 recruitment to the midbody. and S3= 0.0305) and 3.5% (= 0.0427), respectively), none of the other LOXL2-IN-1 HCl myotubularins affected binucleation (Fig. 3 0.0001), and is not a general consequence of myotubularin loss (for example, through global changes in phospholipid levels). The increased number of binucleated cells upon depletion of MTMR3 or MTMR4 was rescued by expression of respective siRNA-resistant variants, indicating that the defects are not caused by off-target effects (Fig. 3and = 0.0173) (Fig. 4and ?and44= 1.6982*10?20) (Fig. 6= 9.8*10?5) (Fig. 6= 0.0055) (Fig. 6= 0.014 and 0.0064, respectively, compared with control CEP55 intensity), whereas expression of wild-type GFP-MTMR3 returned CEP55 levels to control levels (Fig. 6= 0.06). On the other hand, expression of GFP-MTMR4-CCmut (which cannot bind MTMR3 or PLK1) reversed the phenotype, resulting in increased CEP55 intensity at the midbody (= 0.0068), as is observed with MTMR3 depletion and PLK1 inhibition. From this, we conclude these interactions may occur to ensure continued phosphorylation of CEP55 by PLK1 during early mitosis, leading to proper temporal recruitment of appropriate amounts of CEP55, and subsequently ESCRT components, to the midbody. DISCUSSION In this study, we have systematically identified proteinCprotein interactions established by a relatively understudied family of protein phosphatases, the myotubularins. Consistent with previous studies, the myotubularins displayed extensive intra-family interactions,.