In Drosophila, the partition defective (Par) complex containing Par3, Par6 and atypical protein kinase C (aPKC) directs the polarized distribution and unequal segregation of the cell fate determinant Numb during asymmetric cell divisions. Unequal segregation of mammalian Numb has also been observed, but the factors involved are unknown. Here, we identify in vivo phosphorylation sites of mammalian Numb and show that both mammalian and Drosophila Numb interact with, and are substrates for aPKC in vitro. A form of mammalian Numb lacking two protein kinase C (PKC) phosphorylation sites (Numb2A) accumulates at the cell membrane and is refractory to PKC activation. In epithelial cells, mammalian Numb localizes to the basolateral membrane and is excluded from the apical domain, which accumulates aPKC. In contrast, Numb2A is distributed uniformly around the cell cortex. Mutational analysis of conserved aPKC phosphorylation sites in Drosophila Numb suggests that phosphorylation contributes to asymmetric localization of Numb, opposite to aPKC in dividing sensory organ precursor cells. These results suggest a model in which phosphorylation of Numb by aPKC regulates its polarized distribution in epithelial cells as well as during asymmetric cell divisions.
Pubmed ID: 17203073 RIS Download
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A package of over twenty mass spectrometry-based tools primarily geared toward proteomic data analysis and database mining. It can be run from the command line, but is primarily used through a web browser, and there is a public website that allows anyone to use the software without local installation. Tandem mass spectrometry analysis tools are used for database searching and identification of peptides, including post-translationally modified peptides and cross-linked peptides. Support for isotope and label-free quantification from this type of data is provided. MS-Viewer software allows sharing and displaying of annotated spectra from many different tandem mass spectrometry data analysis packages. Other tools include software for analyzing peptide mass fingerprinting data (MS-Fit); prediction of theoretical fragmentation of peptides (MS-Product); theoretical chemical or enzymatic digestion of proteins (MS-Digest); and theoretical modeling of the isotope distribution of any chemical, including peptides (MS-Isotope). Searches using amino acid sequence can be used to identify homologous peptides in a database (MS-Pattern); the use of the combination of amino acid sequence and masses can be used for homologous peptide and protein identification using MS-Homology. Tandem mass spectrometry peak list files can be filtered for the presence of certain peaks or neutral losses using MS-Filter. Given a list of proteins, MS-Bridge can report all potential cross-linked peptide combinations of a specified mass. Given a precursor peptide mass and information about known amino acid presence, absence, or modifications, MS-Comp can report all amino acid combinations that could lead to the observed mass.
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