Rac1 promotes kidney collecting duct integrity by limiting actomyosin activity.

A polarized collecting duct (CD), formed from the branching ureteric bud (UB), is a prerequisite for an intact kidney. The small Rho GTPase Rac1 is critical for actin cytoskeletal regulation. We investigated the role of Rac1 in the kidney collecting system by selectively deleting it in mice at the initiation of UB development. The mice exhibited only a mild developmental phenotype; however, with aging, the CD developed a disruption of epithelial integrity and function. Despite intact integrin signaling, Rac1-null CD cells had profound adhesion and polarity abnormalities that were independent of the major downstream Rac1 effector, Pak1. These cells did however have a defect in the WAVE2-Arp2/3 actin nucleation and polymerization apparatus, resulting in actomyosin hyperactivity. The epithelial defects were reversible with direct myosin II inhibition. Furthermore, Rac1 controlled lateral membrane height and overall epithelial morphology by maintaining lateral F-actin and restricting actomyosin. Thus, Rac1 promotes CD epithelial integrity and morphology by restricting actomyosin via Arp2/3-dependent cytoskeletal branching.

Non-neutralizing Antibodies from a Marburg Infection Survivor Mediate Protection by Fc-Effector Functions and by Enhancing Efficacy of Other Antibodies.

Marburg virus (MARV) and Ebola virus (EBOV) belong to the family Filoviridae. MARV causes severe disease in humans with high fatality. We previously isolated a large panel of monoclonal antibodies (mAbs) from B cells of a human survivor with previous naturally acquired MARV infection. Here, we characterized functional properties of these mAbs and identified non-neutralizing mAbs targeting the glycoprotein (GP) 2 portion of the mucin-like domain (MLD) of MARV GP, termed the wing region. One mAb targeting the GP2 wing, MR228, showed therapeutic protection in mice and guinea pigs infected with MARV. The protection was mediated by the Fc fragment functions of MR228. Binding of another GP2 wing-specific non-neutralizing mAb, MR235, to MARV GP increased accessibility of epitopes in the receptor-binding site (RBS) for neutralizing mAbs, resulting in enhanced virus neutralization by these mAbs. These findings highlight an important role for non-neutralizing mAbs during natural human MARV infection.

Structural Characterization of Pan-Ebolavirus Antibody 6D6 Targeting the Fusion Peptide of the Surface Glycoprotein.

Ebola virus infection causes severe disease in humans and represents a global health threat. Candidates for immunotherapeutics and vaccines have shown promise in clinical trials, although they are ineffective against other members of the Ebolavirus genus that also cause periodic, lethal outbreaks. In this study, we present a crystal structure of a pan-ebolavirus antibody, 6D6, as well as single-particle electron microscopy reconstructions of 6D6 in complex with Ebola and Bundibugyo virus glycoproteins. 6D6 binds to the conserved glycoprotein fusion peptide, implicating it as a site of immune vulnerability that could be exploited to reliably elicit a pan-ebolavirus neutralizing antibody response.

Cdc42 regulates epithelial cell polarity and cytoskeletal function during kidney tubule development.

The Rho GTPase Cdc42 regulates key signaling pathways required for multiple cell functions, including maintenance of shape, polarity, proliferation, migration, differentiation and morphogenesis. Although previous studies have shown that Cdc42 is required for proper epithelial development and maintenance, its exact molecular function in kidney development is not well understood. In this study, we define the specific role of Cdc42 during murine kidney epithelial tubulogenesis by deleting it selectively at the initiation of ureteric bud or metanephric mesenchyme development. Deletion in either lineage results in abnormal tubulogenesis, with profound defects in polarity, lumen formation and the actin cytoskeleton. Ultimately, these defects lead to renal failure. Additionally, in vitro analysis of Cdc42-null collecting duct cells shows that Cdc42 controls these processes by regulating the polarity Par complex (Par3-Par6-aPKC-Cdc42) and the cytoskeletal proteins N-Wasp and ezrin. Thus, we conclude that the principal role of Cdc42 in ureteric bud and metanephric mesenchyme development is to regulate epithelial cell polarity and the actin cytoskeleton.

Cdc42 promotes host defenses against fatal infection.

The small Rho GTPase Cdc42 regulates key signaling pathways required for multiple cell functions, including maintenance of shape, polarity, proliferation, invasion, migration, differentiation, and morphogenesis. As the role of Cdc42-dependent signaling in fibroblasts in vivo is unknown, we attempted to specifically delete it in these cells by crossing the Cdc42(fl/fl) mouse with an fibroblast-specific protein 1 (FSP1)-Cre mouse, which is thought to mediate recombination exclusively in fibroblasts. Surprisingly, the FSP1-Cre;Cdc42(fl/fl) mice died at 3 weeks of age due to overwhelming suppurative upper airway infections that were associated with neutrophilia and lymphopenia. Even though major aberrations in lymphoid tissue development were present in the mice, the principal cause of death was severe migration and killing abnormalities of the neutrophil population resulting in an inability to control infection. We also show that in addition to fibroblasts, FSP1-Cre deleted Cdc42 very efficiently in all leukocytes. Thus, by using this nonspecific Cre mouse, we inadvertently demonstrated the importance of Cdc42 in host protection from lethal infections and suggest a critical role for this small GTPase in innate immunity.