title: The Rsu-1-PINCH1-ILK complex is regulated by Ras activation in tumor cells.
abstract: The link between Ras transformation and enhanced cell migration due to altered integrin signaling is well established in tumorigenesis, however there remain gaps in our understanding of its mechanism. The Ras suppressor, Rsu-1, has recently been linked to the IPP (integrin-linked kinase {ILK}, PINCH-1/LIMS1, parvin) focal adhesion complex based on its interaction with the LIM 5 domain of PINCH1. Defining the role of the Rsu1-PINCH1-ILK-parvin complex in tumorigenesis is important because both ILK and PINCH1 are elevated in certain tumors while ectopic expression of Rsu-1 blocks tumorigenesis. Our studies previously identified an alternatively spliced isoform of Rsu-1 in high-grade gliomas. We report here the detection of a truncated (p29) Rsu-1 protein, which correlates with the presence of the alternatively spliced Rsu-1 RNA. This RNA and the respective protein were detected in human tumor cell lines that contain high levels of activated Ras, and inhibitor studies demonstrate that the Mek-ERK pathway regulates expression of this truncated Rsu-1 product. We also show that Rsu-1 co-localizes with ILK at focal contacts and co-immunoprecipitates with the ILK-PINCH1 complex in non-transformed cells, but following Ras transformation the association of Rsu-1 with the PINCH1-ILK complex is greatly reduced. Using a human breast cancer cell line, our in vitro studies demonstrate that the depletion of Rsu-1 full-length protein enhances cell migration coincident with an increase in Rac-GTP while the depletion of the p29 Rsu-1 truncated protein inhibits migration. These findings indicate that Rsu-1 may inhibit cell migration by stabilizing the IPP adhesion complex and that Ras activation perturbs this inhibitory function by modulating both Rsu-1 splicing and association of full-length Rsu-1 with IPP. Hence, our findings demonstrate that Rsu-1 links the Ras pathway with the IPP complex and the perturbations of cell attachment-dependent signaling that occur in the malignant process.
authors.affiliation: Department of Cell Biology and Oncology, Consorzio Mario Negri Sud, Via Nazionale 8a, I-66030 Santa Maria Imbaro, Italy.
authors.forename: Gerard W
authors.initials: GW
authors.lastname: Dougherty
authors.forename: Cynthia
authors.initials: C
authors.lastname: Jose
authors.forename: Mario
authors.initials: M
authors.lastname: Gimona
authors.forename: Mary Lou
authors.initials: ML
authors.lastname: Cutler
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D017398:Alternative Splicing; D002448:Cell Adhesion; D045744:Cell Line, Tumor; D002465:Cell Movement; D004268:DNA-Binding Proteins / Q000378:metabolism*; D022001:Focal Adhesions; D006801:Humans; D060588:LIM Domain Proteins; D008565:Membrane Proteins; D008856:Microscopy, Fluorescence; D020928:Mitogen-Activated Protein Kinases; D009369:Neoplasms / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D018631:ras Proteins / Q000378:metabolism*; D000099200:Scaffold Protein ILK
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D004268:DNA-Binding Proteins; D060588:LIM Domain Proteins; D008565:Membrane Proteins; D020928:Mitogen-Activated Protein Kinases; D020033:Protein Isoforms; D017346:Protein Serine-Threonine Kinases; D014157:Transcription Factors; D018631:ras Proteins; D000099200:Scaffold Protein ILK; C088088:LIMS1 protein, human; C076224:RSU1 protein, human