Activation of extracellular signal-regulated kinase in proliferative glomerulonephritis in rats

Multiple extracellular mitogens are involved in the pathogenesis of proliferative forms of glomerulonephritis (GN), In vitro studies demonstrate the pivotal role of extracellular signal-regulated kinase (ERK) in the regulation of cellular proliferation in response to extracellular mitogens. In this study, we examined whether this kinase, as a convergence point of mitogenic stimuli, is activated in proliferative GN in vivo, Two different proliferative forms of anti-glomerular basal membrane (GEM) GN in rats were induced and whole cortical tissue as well as isolated glomeruli examined using kinase activity assays and Western blot analysis, Administration of rabbit anti-rat GEM serum to rats, preimmunized with rabbit IgG, induced an accelerated crescentic anti-GEM GN. A significant increase in cortical, and more dramatically glomerular ERK activity was detected at 1, 3, and 7 d after induction of GN, Immunization of Wistar-Kyoto rats with bovine GEM also induced a crescentic anti-GBM GN with an increase of renal cortical ERK activity after 4, 6, and 8 wk, ERK is phosphorylated and activated by the MAP kinase/ERK kinase (MEK), We detected a significant increase in the expression of glomerular MEK in the accelerated form of anti-GEM CN, providing a possible mechanism of long-term activation of ERK in this disease model, In contrast to ERK, activation of stress-activated protein kinase was only detectable at early stages of proliferative GN, indicating these related kinases to serve distinct roles in the pathogenesis of GN, Our observations point to ERK as a putative mediator of the proliferative response to immune injury in GN and suggest that upregulation of MEK is involved in the long-term regulation of ERK in vivo.

Burkholderia cenocepacia requires the RpoN sigma factor for biofilm formation and intracellular trafficking within macrophages

Chronic respiratory infections by Burkholderia cenocepacia in cystic fibrosis patients are associated with increased morbidity and mortality, but virulence factors determining the persistence of the infection in the airways are not well characterized. Using a chronic pulmonary infection model, we previously identified an attenuated mutant with an insertion in a gene encoding an RpoN activator protein, suggesting that RpoN and/or components of the RpoN regulon play a role in B. cenocepacia virulence. In this study, we demonstrate that a functional rpoN gene is required for bacterial motility and biofilm formation in B. cenocepacia K56-2. Unlike other bacteria, RpoN does not control flagellar biosynthesis, as evidenced by the presence of flagella in the rpoN mutant. We also demonstrate that, in macrophages, the rpoN mutant is rapidly trafficked to lysosomes while intracellular wild-type B. cenocepacia localizes in bacterium-containing vacuoles that exhibit a pronounced delay in phagolysosomal fusion. Rapid trafficking to the lysosomes is also associated with the release of red fluorescent protein into the vacuolar lumen, indicating loss of bacterial cell envelope integrity. Although a role for RpoN in motility and biofilm formation has been previously established, this study is the first demonstration that the RpoN regulon in B. cenocepacia is involved in delaying phagolysosomal fusion, thereby prolonging bacterial intracellular survival within macrophages.