PROFILIN - AT THE CROSSROADS OF SIGNAL-TRANSDUCTION AND THE ACTIN CYTOSKELETON

Despite its small size, profilin is an amazingly diverse and sophistic ated protein whose precise role in cells continues to elude the unders tanding of researchers 15 years after its discovery. Its ubiquity, abu ndance and necessity for life in more evolved organisms certainly spea ks for its extreme importance in cell function. So far, three ligands for profilin have been well-characterized in vitro: actin monomers, me mbrane polyphosphoinositides and poly-L-proline. In the years followin g its discovery, profilin's role in vivo progressed from that of a sim ple actin-binding protein which inhibits actin polymerization, to one which, as an important regulator of the cytoskeleton, can even promote actin polymerization under the appropriate circumstances. In addition , interactions with components of the phosphatidylinositol cycle and t he RAS pathway in yeast implicate profilin as an important link throug h which the actin cytoskeleton is able to communicate with major signa ling pathways.