IGFBP-5(201-218) stimulates Cdc42GAP aggregation and filopodia formationin 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 using separate stimulatory and effector pathways. The IGFBP-5 stimulatory pathway is mediated by the serine/threonine kinase IGFBP-5 receptor, which is activated by the carboxy-terminal peptide IGFBP-5201-218. In this study, we examined the direct effects of IGFBP-5201-218 on stimulatory and effector pathways that lead to a change in mesangial cell (MC) phenotype.


METHODS
Rapid actin reorganization, formation of filopodia, and characterization of novel substratum attachment structures that develop during IGFBP-5-mediating migration were examined by light, immunofluorescence, and electron microscopy. Using a wounding assay, migration was measured after the addition of stimulants and inhibitors.


RESULTS
Stimulation of MCs with IGFBP-5201-218 induces rapid actin reorganization and loss of peripheral focal adhesions. The MCs develop long cellular extensions where f-actin and beta-actin terminate in unique substratum attachments. Fluorescence microscopy of stimulated cells shows that Cdc42GAP aggregates within minutes following treatment with IGFBP-5201-218. In contrast, IGF-I increases staining for Rac-1, but not Cdc42GAP, in association with the formation of prominent leading lamellae without filopodia. Staurosporin inhibits cell migration and Cdc42GAP aggregation only when added within the first hour, suggesting that it inhibits the stimulatory effect of IGFBP-5201-218 by blocking the IGFBP-5 receptor serine/threonine kinase activity.


CONCLUSIONS
These data demonstrate that IGFBP-5201-218 preferentially activates Cdc42 and induces the formation of long filopodia with unique substratum attachments that produce a novel mode of locomotion.
Berfield
A K
AK
Division of Nephrology, Department of Medicine, VA Puget Sound Health Care System and University of Washington School of Medicine, Seattle, WA 98108, USA.
Andress
D L
DL
Abrass
C K
CK
D000199:Actins / Q000378:metabolism; D000818:Animals; D002465:Cell Movement / Q000187:drug effects; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000187:drug effects; D005920:Glomerular Mesangium / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000502:physiology; D010446:Peptide Fragments / Q000494:pharmacology*; D051381:Rats; D019311:Staurosporine / Q000494:pharmacology; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*
D000199:Actins; D018975:Insulin-Like Growth Factor Binding Protein 5; D010446:Peptide Fragments; D007334:Insulin-Like Growth Factor I; D020764:cdc42 GTP-Binding Protein; D019311:Staurosporine