Nesprin-3, a novel outer nuclear membrane protein, associates with the cytoskeletal linker protein plectin.

Despite their importance in cell biology, the mechanisms that maintain the nucleus in its proper position in the cell are not well understood. This is primarily the result of an incomplete knowledge of the proteins in the outer nuclear membrane (ONM) that are able to associate with the different cytoskeletal systems. Two related ONM proteins, nuclear envelope spectrin repeat (nesprin)-1 and -2, are known to make direct connections with the actin cytoskeleton through their NH2-terminal actin-binding domain (ABD). We have now isolated a third member of the nesprin family that lacks an ABD and instead binds to the plakin family member plectin, which can associate with the intermediate filament (IF) system. Overexpression of nesprin-3 results in a dramatic recruitment of plectin to the nuclear perimeter, which is where these two molecules are colocalized with both keratin-6 and -14. Importantly, plectin binds to the integrin alpha6beta4 at the cell surface and to nesprin-3 at the ONM in keratinocytes, suggesting that there is a continuous connection between the nucleus and the extracellular matrix through the IF cytoskeleton.

Differential roles of CD14 and toll-like receptors 4 and 2 in murine Acinetobacter pneumonia.

RATIONALE: Acinetobacter baumannii is an opportunistic bacterial pathogen that is increasingly associated with gram-negative nosocomial pneumonia, but the molecular mechanisms that play a role in innate defenses during A. baumannii infection have not been elucidated. OBJECTIVE: To gain first insight into the role of CD14 and Toll-like receptors 4 and 2 in host response to A. baumannii pneumonia. METHODS: Respective gene-deficient mice were intranasally infected with A. baumannii, and bacterial outgrowth, lung inflammation, and pulmonary cytokine/chemokine responses were determined. To study the importance of LPS in the inflammatory response, mice were also challenged with A. baumannii LPS. MEASUREMENTS AND MAIN RESULTS: Bacterial counts were increased in CD14 and Toll-like receptor 4 gene-deficient mice, and only these animals developed bacteremia. The pulmonary cytokine/chemokine response was impaired in Toll-like receptor 4 knockout mice and the onset of lung inflammation was delayed. In contrast, Toll-like receptor 2-deficient animals displayed an earlier cell influx into lungs combined with increased macrophage inflammatory protein-2 and monocyte chemoattractant protein-1 concentrations, which was associated with accelerated elimination of bacteria from the pulmonary compartment. Neither CD14 nor Toll-like receptor 4 gene-deficient mice responded to intranasal administration of LPS, whereas Toll-like receptor 2 knockout mice were indistinguishable from wild-type animals. CONCLUSIONS: Our results suggest that CD14 and Toll-like receptor 4 play a key role in innate sensing of A. baumannii via the LPS moiety, resulting in effective elimination of the bacteria from the lung, whereas Toll-like receptor 2 signaling seems to counteract the robustness of innate responses during acute A. baumannii pneumonia.