Publications

The Streptococcus gordonii cell surface glycoprotein GspB mediates high-affinity binding to distinct sialylated carbohydrate structures on human platelets and salivary proteins. GspB is glycosylated in the cytoplasm of S. gordonii and is then transported to the cell surface via a dedicated transport system that includes the accessory Sec components SecA2 and SecY2. The means by which the GspB preprotein is selectively recognized by the accessory Sec system have not been characterized fully. GspB has a 90-residue amino-terminal signal sequence that displays a traditional tripartite structure, with an atypically long amino-terminal (N) region followed by hydrophobic (H) and cleavage regions. In this report, we investigate the relative importance of the N and H regions of the GspB signal peptide for trafficking of the preprotein. The results show that the extended N region does not prevent export by the canonical Sec system. Instead, three glycine residues in the H region not only are necessary for export via the accessory Sec pathway but also interfere with export via the canonical Sec route. Replacement of the H-region glycine residues with helix-promoting residues led to a decrease in the efficiency of SecA2-dependent transport of the preprotein and a simultaneous increase in SecA2-independent translocation. Thus, the hydrophobic core of the GspB signal sequence is responsible primarily for routing towards the accessory Sec system.

RATIONALE

Mechanical ventilation with high tidal volumes leads to increased permeability, generation of inflammatory mediators, and damage to alveolar epithelial cells (ATII).

OBJECTIVES

To identify changes in the ATII proteome after two different ventilation strategies in rats.

METHODS

Rats (n = 6) were ventilated for 5 hours with high- and low tidal volumes (VTs) (high VT: 20 ml/kg; low VT: 6 ml/kg). Pooled nonventilated rats served as control animals. ATII cells were isolated and lysed, and proteins were tryptically cleaved into peptides. Cellular protein content was evaluated by peptide labeling of the ventilated groups with (18)O. Samples were fractionated by cation exchange chromatography and identified using electrospray tandem mass spectrometry. Proteins identified by 15 or more peptides were statistically compared using t tests corrected for the false discovery rate.

MEASUREMENTS AND MAIN RESULTS

High Vt resulted in a significant increase in airspace neutrophils without an increase in extravascular lung water. Compared with low-VT samples, high-VT samples showed a 32% decrease in the inositol 1,4,5-trisphosphate 3 receptor (p < 0.01), a 34% decrease in Na(+), K(+)-ATPase (p < 0.01), and a significantly decreased content in ATP synthase chains. Even low-VT samples displayed significant changes, including a 66% decrease in heat shock protein 90-beta (p < 0.01) and a 67% increase in mitochondrial pyruvate carboxylase (p < 0.01). Significant differences were found in membrane, acute phase, structural, and mitochondrial proteins.

CONCLUSIONS

After short-term exposure to high-VT ventilation, significant reductions in membrane receptors, ion channel proteins, enzymes of the mitochondrial energy system, and structural proteins in ATII cells were present. The data supports the two-hit concept that an unfavorable ventilatory strategy may make the lung more vulnerable to an additional insult.

The erythromycin breath test (EBT) is a standard test used to evaluate the extent of CYP3A4 activity. This study examines whether presumed changes in CYP3A4 activity are in fact related to inhibition of an uptake organic anion transporter using rifampin and inhibition of the efflux hepatic P-glycoprotein transporter using lansoprazole. Three EBT tests in healthy adults were conducted: EBT alone, with lansoprazole, and with rifampin. For all subjects, lansoprazole treatment increased respiratory (14)C excretion by +0.25+/-0.51 met/h (P=0.07) and rifampin decreased (14)C excretion by -0.44+/-0.40 met/h (P<0.001) compared with baseline. Comparing lansoprazole to rifampin, (14)C excretion increased by +0.69+/-0.50 met/h (P<0.001). Only women had significant changes after drug infusion: (14)C excretion after rifampin -0.40+/-0.36 met/h (P=0.018) and +0.47+/-0.44 met/h (P=0.018) after lansoprazole. Relying on EBT without considering transporter interactions can lead to errors in interpreting the degree of CYP3A4 metabolism.

To study air space fluid clearance (AFC) under conditions that resemble the clinical setting of pulmonary edema in patients, we developed a new perfused human lung preparation. We measured AFC in 20 human lungs rejected for transplantation and determined the contribution of AFC to lung fluid balance. AFC was then compared with air space and perfusate levels of a biological marker of epithelial injury. The majority of human lungs rejected for transplant had intact basal (75%) and beta(2)-adrenergic agonist-stimulated (70%) AFC. For lungs with both basal and stimulated AFC, the basal AFC rate was 19 +/- 10%/h, and the beta(2)-adrenergic-stimulated AFC rate was 43 +/- 13%/h. Higher rates of AFC were associated with less lung weight gain (Pearson coefficient -0.90, P < 0.0001). Air space and perfusate levels of the type I pneumocyte marker receptor for advanced glycation end products (RAGE) were threefold and sixfold higher, respectively, in lungs without basal AFC compared with lungs with AFC (P < 0.05). These data show that preserved AFC is a critical determinant of favorable lung fluid balance in the perfused human lung, raising the possibility that beta(2)-agonist therapy to increase edema fluid clearance may be of value for patients with acute lung injury and pulmonary edema. Also, although additional studies are needed, a biological marker of alveolar epithelial injury may be useful clinically in predicting preserved AFC.

Matrix metalloproteinase-2 (MMP-2, gelatinase A) plays an essential role in angiogenesis, inflammation, and fibrosis. These processes are critical for wound healing and accordingly elevated levels of MMP-2 expression have been detected after skin injury. Our goal was to investigate the transcriptional activation of the MMP-2 gene in a model of skin injury by using two different MMP-2/LacZ-reporter mice. Upon skin injury MMP-2 expression was upregulated, whereas tissue from normal skin stained negative except for occasional macrophages, sweat glands, and hair follicles. Skin injury also activated MMP-2 proteolytic activity and reporter gene expression. We demonstrate that MMP-2 regulatory sequences -1686/+423 drive appropriate injury-induced MMP-2-promoter activation. Reporter gene expression was predominantly detectable in endothelial cells and in macrophages. Deletion of the 5' responsive element, denoted RE-1, residing at -1241/+423 bp of the regulatory sequence led to abrogated MMP-2 transcription in vivo. The findings define a crucial role for the enhancer element RE-1 in injury-induced MMP-2 transcription of the skin.