Domain analysis of α-actinin reveals new aspects of its association with F-actin during cytokinesis

alpha-actinin is a rod-shaped actin cross-linking protein composed of actin binding domain, spectrin-like repeats of the central rod domain and the EF-hand domain. Cytokinesis in mammalian cells involves remodeling of equatorial actin filaments (F-actin) mediated by alpha-actinin However, it remains unknown how alpha-actinin interacts with F-actin at the cleavage furrow. To address this question, we have conducted functional analysis of the mutant that either lacks the ability to cross-link F-actin (ABD) or to bind to F-actin (Delta ABD) We found that equatorial localization of alpha-actinin requires both its F-actin binding and cross-linking activities. Unexpectedly, we also found that overexpression of Delta ABD-GFP but not ABD-GFP frequently caused accelerated cytokinesis and ectopic furrowing similar to those observed in cells depleted of alpha-actinin. Immunofluorescence revealed that overexpression of Delta ABD-GFP caused displacement of endogenous alpha-actinin and a decrease in the density of F-actin throughout the entire cortex. Biochemical experiments showed that Delta ABD was able to form heterodimers with endogenous alpha-actinin. These results suggest that the central rod spectrin-like repeats of alpha-actinin is sufficient for its dimerization in viva Our findings uncover previously unappreciated functions of the alpha-actinin domains in a cell. (C) 2010 Elsevier Inc All rights reserved.