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.

LRRC8 proteins share a common ancestor with pannexins, and may form hexameric channels involved in cell‐cell communication

“…One of its subfamilies, Scribble (LAP4), regulates the MAP kinase cascade [67]. RSU1 regulates cell-adhesion and participates in the RAS signal transduction pathway, which is MAP kinasemediated [47]. SHOC2 is a regulatory subunit of phosphatase 1, and provides a scaffold for the interaction between M-Ras and Raf1, activating the MAPK cascade [48].…”

“…LANO lost the PDZ domain and is involved in homeostasis of epithelial tissues and tumour growth [46]. Ras suppressor protein 1 (RSU1) prevents Ras oncogene-induced transformation and may inhibit cell migration [47]. SHOC2 is a scaffold protein that modulates Ras-dependent activation of Raf1 [48].…”

PINCH-1 promotes Bcl-2-dependent survival signalling and inhibits JNK-mediated apoptosis in the primitive endoderm.

“…We next sought to elucidate the mechanism by which PINCH-1 regulates JNK activity in PrE cells. PINCH-1 interacts with RSU-1, which was shown to negatively regulate the activity of JNK (Masuelli and Cutler, 1996;Kadrmas et al, 2004;Dougherty et al, 2008). To determine the level as well as spatial expression pattern of RSU-1 during peri-implantation, we performed immunostaining of E6.5 embryos and of 7-day-old cystic EBs using a specific antibody against RSU-1.…”

“…PINCH-1 can bind several actin modulating proteins (Legate et al, 2006;Wickström et al, 2010), the Ras suppressor protein 1 (RSU-1) and the protein phosphatase 1a (PP1a). The latter two interactions were shown to modulate MAPK and phosphoinositol 3-kinase (PI3K)/AKT signalling, respectively (Masuelli and Cutler, 1996;Dougherty et al, 2008;Eke et al, 2010).…”

The Ras suppressor-1 (RSU-1) in cancer

“…Also, RSU-1 depletion resulted in reduced expression level of PINCH-1, a known binding partner of RSU-1, in one study, and in elevated expression of PINCH-1 in another study [15,20] . Finally, regarding other cellular functions in which RSU-1 is implicated, there are studies showing that RSU-1 promotes cell adhesion, spreading and migration, and promotes cancer cell invasion, while there is a study showing that RSU-1 inhibits cancer cell migration and invasion [16,20,21] .…”