ABSTRACT
SPIN90 is a key regulator of actin cytoskeletal organization. Using the BioGRID(beta) database (General Repository for Interaction Datasets), we identified IRSp53 as a binding partner of SPIN90, and confirmed the in vivo formation of a SPIN90-IRSp53 complex mediated through direct association of the proline-rich domain (PRD) of SPIN90 with the SH3 domain of IRSp53. SPIN90 and IRSp53 positively cooperated to mediate Rac activation, and co-expression of SPIN90 and IRSp53 in COS-7 cells led to the complex formation of SPIN90-IRSp53 in the leading edge of cells. PDGF treatment induced strong colocalization of SPIN90 and IRSp53 at membrane protrusions. Within such PDGF-induced protrusions, knockdown of SPIN90 protein using siRNA significantly reduced lamellipodia-like protrusions as well as localization of IRSp53 at those sites. Finally, competitive inhibition of SPIN90-IRSp53 binding by SPIN90 PRD dramatically reduced ruffle formation, further suggesting that SPIN90 plays a key role in the formation of the membrane protrusions associated with cell motility.
Subject(s)
Adaptor Proteins, Signal Transducing/metabolism , Cell Membrane/metabolism , Muscle Proteins/metabolism , Nerve Tissue Proteins/metabolism , rac GTP-Binding Proteins/metabolism , Adaptor Proteins, Signal Transducing/genetics , Animals , COS Cells , Cell Membrane/ultrastructure , Cell Movement/physiology , Cell Surface Extensions , Chlorocebus aethiops , Gene Knockdown Techniques , Genetic Vectors/metabolism , Humans , Muscle Proteins/genetics , Platelet-Derived Growth Factor/pharmacology , RNA, Small Interfering/metabolism , TransfectionABSTRACT
We recently reported that SPIN90 is able to bind with several proteins involved in regulating actin cytoskeleton networks, including dynamin, WASP, beta PIX, and Nck. Based on these findings, we investigated how SPIN90 regulates the actin cytoskeleton and promotes actin assembly. This study demonstrated that aluminium fluoride-induced localization of SPIN90 to lamellipodia requires amino acids 582-722 at the SPIN90 C-terminus, which is also essential for F-actin binding and Arp2/3 complex mediated polymerization of actin into branched actin filaments. Furthermore, after deletion of the F-actin binding region (582-722 SPIN90) failed to localize at the membrane edge and was unable to promote lamellipodia formation, suggesting that the F-actin binding region in the SPIN90 C-terminus is essential for the formation of branched actin networks and regulation of the actin cytoskeleton at the leading edge of cells.
