New anti-actin drugs in the study of the organization and function of the actin cytoskeleton.

The high degree of structural and molecular complexity of the actin-based cytoskeleton, combined with its ability to reorganize rapidly and locally in response to stimuli, and its force-generating properties, have made it difficult to assess how the different actin structures are assembled in cells, and how they regulate cell behavior. An obvious approach to study the relationships between actin organization, dynamics, and functions is the specific perturbation of actin structures using pharmacological means. Until recently there were only a few agents available that interfered with cellular activities by binding to actin and most of our knowledge concerning the involvement of actin in basic cellular processes was based on the extensive use of the cytochalasins. In recent years we have identified an increasing number of actin-targeted marine natural products, including the latrunculins, jasplakinolides (jaspamides), swinholide A, misakinolide A, halichondramides, and pectenotoxin II, which are discussed in this article. All these marine-sponge-derived compounds are unusual macrolides and can be classified into several major families, each with its own distinct chemical structures. We describe the current state of knowledge concerning the actin-binding properties of these compounds and show that each class of drugs alters the distribution patterns of actin in a unique way, and that even within a chemical class, structurally similar compounds can have different biochemical properties and cellular effects. We also discuss the effects of these new drugs on fenestrae formation in liver endothelial cells as an example of their usefulness as powerful tools to selectively unmask actin-mediated dynamic processes.