CD2AP links cortactin and capping protein at the cell periphery to facilitate formation of lamellipodia

Understanding the physiology of complex relationships between components of signaling pathways and the actin cytoskeleton is an important challenge. CD2AP is a membrane scaffold protein implicated in a variety of physiological and disease processes. The physiological function of CD2AP is unclear, but its biochemical interactions suggest that it has a role in dynamic actin assembly. Here, we report that CD2AP functions to facilitate the recruitment of actin capping protein (CP) to the Src kinase substrate, cortactin, at the cell periphery, and that this is necessary for formation of the short branched filaments that characterize lamellipodium formation and are required for cell migration. Superresolution fluorescence microscopy demonstrated that the efficient colocalization of CP and cortactin at the cell periphery required CD2AP. As both cortactin and CP function to enhance branched actin filament formation, CD2AP functions synergistically to enhance the function of both proteins. Our data demonstrate how the interplay between specialized actin regulatory molecules shapes the actin cytoskeleton

The Stress-Induced Virulence Protein InlH Controls Interleukin-6 Production during Murine Listeriosis ▿

The genome of the pathogenic bacterium Listeria monocytogenes contains a family of genes encoding proteins with a leucine-rich repeat domain. One of these genes, inlH, is a σB-dependent virulence gene of unknown function. Previously, inlH was proposed to be coexpressed with two adjacent internalin genes, inlG and inlE. Using tiling arrays, we showed that inlH expression is monocistronic and specifically induced in stationary phase as well as in the intestinal lumen of mice, independent of inlG and inlE expression. Consistent with inlH σB-dependent regulation, surface expression of the InlH protein is induced when bacteria are subjected to thermal, acidic, osmotic, or oxidative stress. Disruption of inlH increases the amount of the invasion protein InlA without changing inlA transcript level, suggesting that there is a link between inlH expression and inlA posttranscriptional regulation. However, in contrast to InlA, InlH does not contribute to bacterial invasion of cultured cells in vitro or of intestinal cells in vivo. Strikingly, the reduced virulence of inlH-deficient L. monocytogenes strains is accompanied by enhanced production of interleukin-6 (IL-6) in infected tissues during the systemic phase of murine listeriosis but not by enhanced production of any other inflammatory cytokine tested. Since InlH does not modulate IL-6 secretion in macrophages at least in vitro, it may play a role in other immune cells or contribute to a pathway that modulates survival or activation of IL-6-secreting cells. These results strongly suggest that InlH is a stress-induced surface protein that facilitates pathogen survival in tissues by tempering the inflammatory response

Identification of a Novel Inhibitory Actin-capping Protein Binding Motif in CD2-associated Protein

CD2-associated protein (CD2AP) is a scaffold molecule that plays a critical role in the maintenance of the kidney filtration barrier. Little, however, is understood about its mechanism of function. We used mass spectrometry to identify CD2AP-interacting proteins. Many of the proteins that we identified suggest a role for CD2AP in endocytosis and actin regulation. To address the role of CD2AP in regulation of the actin cytoskeleton, we focused on characterizing the interaction of CD2AP with actin-capping protein CP. We identified a novel binding motif LXHXTXXRPK(X)6P present in CD2AP that is also found in its homolog Cin85 and other capping protein-associated proteins such as CARMIL and CKIP-1. CD2AP inhibits the function of capping protein in vitro. Therefore, our results support a role of CD2AP in the regulation of the actin cytoskeleton