In the present study, we show that transforming growth factor /3 (TGF-P) strongly inhibits fibroblast growth factor-induced proliferation and motility of bovine endothelial cells in tissue culture. TGF-fi also prevents the phorbol ester-induced invasion of capillary endothelial cells into collagen matrices-i.e., blocks angiogenesis in vitro.

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IntroductionInactivation of proteins that participate in more than one cellular process leads to a variety of apparently unconnected phenotypes. Understanding the molecular cause for each phenotype might reveal how seemingly independent cellular processes are regulated and coordinated in the cell. Genome-wide gene interaction data based on the simultaneous inactivation of more than one gene greatly facilitate this inherently complex analysis because genes with pleiotropic phenotypes often occupy central positions in the corresponding interaction networks (Costanzo et al., 2010;Tong et al., 2004). By assigning physical connections, protein-protein interaction maps provide the necessary complementary information. Interpretation of these maps is usually not straightforward. Genetic interactions can result from complex functional relationships between the investigated pairs of genes and protein interaction maps are generally projections of contacts that occur at different times and places in the cell. To transform protein interaction data into mechanistically meaningful models, it is necessary to resolve these projections into their different interaction planes. We define an interaction plane or state as the sum of all simultaneously occurring contacts. Ideally, these states should be defined by time-and space-resolved in vivo studies. However, these studies are technically demanding and usually not suited for measuring multiple contacts (Maeder et al., 2007). Using the protein pair Ptc1p-Nbp2p of the yeast Saccharomyces cerevisiae as an example and the split-ubiquitin method (SplitUb) as the experimental tool, we present an alternative approach for defining interaction states. The derived constraint interaction network reduces the number of possible states and thus provides a useful framework for model building and the initiation of more detailed studies.

SummaryAn understanding of cytokinesis at the molecular level requires a detailed description of the protein complexes that perform central activities during this process. The proteins Hof1p, Cyk3p, Inn1p and Myo1p each represent one of the four genetically defined and partially complementary pathways of cytokinesis in the yeast Saccharomyces cerevisiae. Here we show that the osmosensor Sho1p is required for correct cell-cell separation. Shortly before cytokinesis Sho1p sequentially assembles with Hof1p, Inn1p and Cyk3p, into a complex (the HICS complex) that might help to connect the membrane with the actin-myosin ring. The HICS complex is formed exclusively through interactions between three SH3 domains located in Cyk3p, Hof1p and Sho1p, and five acceptor sites found in Cyk3p, Hof1p and Inn1p. Owing to the overlapping binding specificities of its members the HICS complex is best described as ensembles of isomeric interaction states that precisely coordinate the different functions of the interactors during cytokinesis.

Fibroblast growth factor (FGF) receptor (FGFR) signaling controls the migration of glial, mesodermal, and tracheal cells in Drosophila melanogaster. Little is known about the molecular events linking receptor activation to cytoskeletal rearrangements during cell migration. We have performed a functional characterization of Downstream-of-FGFR (Dof), a putative adapter protein that acts specifically in FGFR signal transduction in Drosophila. By combining reverse genetic, cell culture, and biochemical approaches, we demonstrate that Dof is a specific substrate for the two Drosophila FGFRs. After defining a minimal Dof rescue protein, we identify two regions important for Dof function in mesodermal and tracheal cell migration. The N-terminal 484 amino acids are strictly required for the interaction of Dof with the FGFRs. Upon receptor activation, tyrosine residue 515 becomes phosphorylated and recruits the phosphatase Corkscrew (Csw). Csw recruitment represents an essential step in FGF-induced cell migration and in the activation of the Ras/MAPK pathway. However, our results also indicate that the activation of Ras is not sufficient to activate the migration machinery in tracheal and mesodermal cells. Additional proteins binding either to the FGFRs, to Dof, or to Csw appear to be crucial for a chemotactic response.Fibroblast growth factor (FGF) receptors (FGFRs) control diverse cellular processes, including cell proliferation, differentiation, migration, and survival during metazoan development (for reviews, see references 29 and 31). FGFRs belong to a large family of transmembrane receptor tyrosine kinases (RTK) and activate a variety of downstream signaling molecules. The transcriptional responses to FGFR activation are elicited, at least in part, via the Ras/mitogen-activated protein kinase (MAPK) pathway and the phosphorylation of Ets-domain-containing transcriptional regulators (25). Specific responses in the nucleus are then most likely determined by interactions with preexisting nuclear components on genomic enhancers or repressor elements (1,20,40). Much less is known about how RTK signaling or FGFR signaling in particular regulates cytoplasmic events in the control of cell movement.In Drosophila melanogaster, FGFR signaling has been implicated in the migration of several tissues, notably, in the spreading of mesoderm, the migration of tracheal cells and glial cells in the embryo, and the recruitment of mesodermal cells into the genital disk and in the formation of air sacs during larval stages (2,4,11,12,18,36). In vivo imaging in live Drosophila embryos has shown that FGFR signaling indeed leads to dynamic cytoskeletal reorganizations during migration, resulting in the formation of filopodial extensions in tip cells (33,36). Despite the importance of FGFR signaling in cell migration in Drosophila, the molecular events linking signal reception to these cytoskeletal events remain elusive.Similar to other RTKs, FGFRs are activated by receptor dimerization upon ligand binding, which then leads to activation of...