IGFBP-5(201-218) stimulates Cdc42GAP aggregation and filopodia formation in migrating mesangial cells

Background We have previously shown that insulin-like growth factor-I (IGF- I) and IGF binding protein-5 (IGFBP-5) induce mesangial cell migration usin g separate stimulatory and effector pathways. The IGFBP-5 stimulatory pathw ay is mediated by the serine/threonine kinase IGFBP-5 receptor, which is ac tivated by the carboxy-terminal peptide IGFBP-5(201-218). In this study, we examined the direct effects of IGFBP-5(201-218) On stimulatory and effecto r pathways that lead to a change in mesangial cell (MC) phenotype. Methods. Rapid actin reorganization, formation of filopodia, and characteri zation of novel substratum attachment structures that develop during IGFBP- 5-mediating migration were examined by light, immunofluorescence, and elect ron microscopy. Using a wounding assay, migration was measured after the ad dition of stimulants and inhibitors. Results. Stimulation of MCs with IGFBP-5(201-218) induces rapid actin reorg anization and loss of peripheral focal adhesions. The MCs develop long cell ular extensions where f-actin and beta-actin terminate in unique substratum attachments. Fluorescence microscopy of stimulated cells shows that Cdc42G AP aggregates within minutes following treatment with IGFBP-5(201-218). I, contrast, IGF-I increases staining for Rac-1, but not Cdc42GAP, in associat ion with the formation of prominent leading lamellae without filopodia. Sta urosporin inhibits cell migration and Cdc42GAP aggregation only when added within the first hour, suggesting that it inhibits the stimulatory effect o f IGFBP-5(201-218) by blocking the IGFBP-5 receptor serine/threonine kinase activity. Conclusions. These data demonstrate that IGFBP-5(201-218) preferentially ac tivates Cdc42 and induces the formation of long filopodia with unique subst ratum attachments that pro duce a novel mode of locomotion.