A functional link between dynamin and the actin cytoskeleton at podosomes

Cell transformation by Rous sarcoma virus results in a dramatic change of a dhesion structures with the substratum. Adhesion plaques are replaced by do t-like attachment sites called podosomes Podosomes are also found constitut ively in motile nontransformed cells such as leukocytes, macrophages, and o steoclasts. They are represented by columnar arrays of actin which are perp endicular to the substratum and contain tubular invaginations of the plasma membrane. Given the similarity of these tubules to those generated by dyna min around a variety of membrane templates we investigated whether dynamin is present at podosomes. Immunoreactivities for dynamin 2 and for the dynam in 2-binding protein endophilin 2 (SH3P8) were detected at podosomes of tra nsformed cells and osteoclasts. Furthermore, GFP wild-type dynamin 2aa was targeted to podosomes. As shown by fluorescence recovery after photobleachi ng, GFP-dynamin 2aa and GFP-actin had a very rapid and similar turnover at podosomes. Expression of the GFP-dynamin 2aa(G273D) abolished podosomes whi le GFP-dynamin(K44A) was targeted to podosomes but delayed actin turnover. These data demonstrate a functional link between a member of the dynamin fa mily and actin at attachment sites between cells and the substratum.