Actin and actin-binding proteins II. The pathological aspects

The vast variety of cellular processes implicating the actin molecule, as e ither a component of the cytoskeleton or a major factor in muscle contracti on and motility systems, requires the interactions of actin with its associ ated proteins. A fascinating example of actin-based motility in non-muscle cells is the case of the bacteria Listeria monocytogenes, which can invade eukaryotic cells and actively exploit actin from its host cell during infec tion and cell-to-cell spreading. Within the cell, the regulation of continu ous cycle of assembly/disassembly of actin is highly controlled by a large repertoire of proteins acting either individually or in concert, by sequest ering monomers (beta -thymosin), capping (CapZ), cross-linking (filamin), b undling (alpha -actinin), severing (gelsolin) or stabilizing (tropomyosin) actin filaments. The development and function of multicellular organisms ar e dependent on the correct spatial and temporal organization of actin cytos keleton, in response to appropriate environmental cues. Therefore, disrupti ons in the expression, the structure or the function of these proteins resu lt in changes in cell behavior, leading to perturbation of actin architectu re and in many cases, to the appearance of a wide range of pathogenic condi tions and diseases. Indeed, disorganization of the actin cytoskeleton is pa rt of the cell death program.