The intrinsic ability of AFAP-110 to alter actin filament integrity is linked with its ability to also activate cellular tyrosine kinases

The actin filament-associated protein of 110 kDa (AFAP-110) is a Src bindin g partner that represents a potential modulator of actin filament integrity in response to cellular signals. Previous reports have demonstrated that A FAP-110 is capable of directly binding and altering actin filaments. Deleti on of the leucine zipper motif of AFAP-110 (AFAP-110(Delta lzip)) has been shown to induce a phenotype which resembles Src-transformed cells, by repos itioning actin filaments into rosettes. This deletion also mimics a conform ational change in AFAP-110 that is detected in Src-transformed cells. The r esults presented here indicate that unlike AFAP-110, AFAP-110 Delta lzip is capable of activating cellular tyrosine kinases, including Src family memb ers, and that AFAP-110 Delta lzip itself is hyperphosphorylated. The newly tyrosine phosphorylated proteins and activated Src-family members appear to be associated with actin-rich lamellipodia. A point mutation that alters t he SH3-binding motif of AFAP-110 Delta lzip prevents it from activating tyr osine kinases and altering actin filament integrity. In addition, a deletio n within a pleckstrin homology (PH) domain of AFAP-110 Delta lzip will also revert its effects upon actin filaments. Lastly, dominant-positive RhoA(V1 4) will block the ability of AFAP-110(Delta lzip) from inducing actin filam ent rosettes, but does not inhibit Src activation. Thus, conformational cha nges in AFAP-110 enable it to activate cellular kinases in a mechanism requ iring SH3 and/or PH domain interactions. We hypothesize that cellular signa ls which alter AFAP-110 conformation, enable it to activate cellular kinase s such as cSrc, which then direct changes in actin filament integrity in a Rho-dependent fashion.