Integrons constitute a novel family of DNA elements which evolved by site-specific integration of discrete units between two conserved segments. On the In4 integron of Tnl696, a precisely inserted gene cassette of 1,549 bp conferring nonenzymatic chloramphenicol resistance (cmU) is present between the streptomycinspectinomycin resistance (aad42) gene cassette and the 3'-conserved segment of the integron. In this study, we present the nucleotide sequence of the cmlA gene cassette of Tn1696, show its similarity to bacterial efflux systems and other transport proteins, and present evidence for alterations that its expression exerts on bacterial membranes. The cmlA gene cassette apparently carries its own promoter(s), a situation that has not heretofore been observed in the integrons of multiresistance plasmids and transposons of gram-negative bacteria. One or more of these promoters were shown to be functionally active in expressing a cat marker gene from promoter-probe vectors. The putative CmIA polypeptide appears to provoke a reduction of the content of the major porins OmpA and OmpC.Multiresistance plasmids and transposons are actively involved in the dissemination of antibiotic resistance determinants, and evidence for their evolution by site-specific integration of antibiotic resistance genes has been reported in recent years. The characterization of multiresistance elements, plasmids and transposons, related to bacterial transposon Tn2J revealed that rearrangements involving antibiotic resistance genes were occurring in the vicinity of the streptomycin-spectinomycin (aadA) and sulfonamide (sull) resistance regions (20,40,50,56,62,63). Stokes and Hall (55) have defined the elements borne on these multiresistance plasmids and transposons as integrons, a novel family of potentially mobile DNA elements which are composed of two conserved segments between which discrete units, ordinarily antibiotic resistance genes, have been integrated as gene cassettes. The 5'-conserved segment encodes a site-specific recombinase (Int) showing active-site residue similarity with the phage integrases (31,41,55). The 3'-conserved segment encodes a sulfonamide-resistant dihydropteroate synthase (Sull [56]) and two open reading frames (ORFs) of unknown phenotype, ORF4 and ORF5 (see Fig. 2A). The integrated gene cassettes encode resistance determinants, such as those for aminoglycoside acetyltransferases and adenylyltransferases, P-lactamases, trimethoprim-resistant dihydrofolate reductases, and enzymatic (acetyltransferase) and nonenzymatic resistance to chloramphenicol. Cassettes carrying ORFs of unknown function are also part of some integrons. No promoters have as yet been found on these gene cassettes, their transcription being driven by promoters located on the 5'-conserved * Corresponding author. t Present address:

The objective of this study was to assess the long-term effects of beta-blockade on survival and left ventricular (LV) remodeling in rats with aortic valve regurgitation (AR). The pharmacological management of chronic AR remains controversial. No drug has been definitively proven to delay the need for valve replacement or to affect morbidity and/or mortality. Our group has reported that the adrenergic system is activated in an animal model of AR and that adrenergic blockade may help maintain normal LV function. The effects of prolonged treatment with a beta-blocker are unknown. Forty Wistar rats with severe AR were divided into 2 groups of 20 animals each and treated with metoprolol (Met, 25 mg.kg(-1).day(-1)) or left untreated for 1 yr. LV remodeling was evaluated by echocardiography. Survival was assessed by Kaplan-Meir curves. Hearts were harvested for tissue analysis. All Met-treated animals were alive after 6 mo vs. 70% of untreated animals. After 1 yr, 60% of Met-treated animals were alive vs. 35% of untreated animals (P = 0.028). All deaths, except one, were sudden. There were no differences in LV ejection fraction (all >50%) or LV dimensions. LV mass tended to be lower in the Met-treated group. There was less subendocardial fibrosis in this group, as well as lower LV filling pressures (LV end-diastolic pressure). beta-Adrenergic receptor ratio (beta(1)/beta(2)) was improved. One year of treatment with Met was well tolerated. Met improved 1-yr survival, minimized LV hypertrophy, improved LV filling pressures, decreased LV subendocardial fibrosis, and helped restore the beta-adrenergic receptor ratio.

Background: Exercise training has beneficial effects in patients with heart failure

Epithelial cells such as hepatocytes exhibit highly polarized properties as a result of the asymmetric distribution of subsets of receptors at unique portions of the surface membrane. While the proper targeting of these surface receptors and maintenance of the resulting polarity depend on microtubules (MTs), the Golgi sorting compartment, and different actin-filament networks, the contribution of keratin intermediate filaments (IFs) has been unclear. Recent data show that the latter cytoskeletal network plays a predominant role in providing resistance to various forms of stress and to apoptosis targeted to the surface membrane. In this context, we first summarize our knowledge of the domain- or assembly-related features of IF proteins and the dynamic properties of IF networks that may explain how the same keratin pair K8/K18 can exert multiple resistance-related functions in simple epithelial cells. We then examine the contribution of linker protein(s) that integrate interactions of keratin IFs with MTs and the actin-cytoskeleton network, polarity-dependent surface receptors and cytoplasmic organelles. We next address likely molecular mechanisms by which K8/K18 can selectively provide resistance to a mechanical or toxic stress, or to Fas-mediated apoptosis. Finally, these issues on keratin structure-function are examined within a context of pathological anomalies emerging in tissue architecture as a result of natural or targeted mutations, or posttranslational modifications at specific amino acid residues. Clearly. the data accumulated in recent years provide new and significant insights on the role of K8/K18, particularly under conditions where polarized cells resist to stressful or apoptotic insults.