Biomedical subjects

I Simonovic

Publications and source records attributed to I Simonovic.

10 recordsLinked to original sources

PubMed2001

Enteropathogenic Escherichia coli activates ezrin, which participates in disruption of tight junction barrier function.

Enteropathogenic Escherichia coli (EPEC) is an important human intestinal pathogen, especially in infants. EPEC adherence to intestinal epithelial cells induces the accumulation of a number of cytoskeletal proteins beneath the bacteria, including the membrane-cytoskeleton linker ezrin. Evidence suggests that ezrin can participate in signal transduction. The aim of this study was to determine whether ezrin is activated following EPEC infection and if it is involved in the cross talk with host intestinal epithelial cells. We show here that following EPEC attachment to intestinal epithelial cells there was significant phosphorylation of ezrin, first on threonine and later on tyrosine residues. A significant increase in cytoskeleton-associated ezrin occurred following phosphorylation, suggesting activation of this molecule. Nonpathogenic E. coli and EPEC strains harboring mutations in type III secretion failed to elicit this response. Expression of dominant-negative ezrin significantly decreased the EPEC-elicited association of ezrin with the cytoskeleton and attenuated the disruption of intestinal epithelial tight junctions. These results suggest that ezrin is involved in transducing EPEC-initiated signals that ultimately affect host physiological functions.

Animals↗

PubMed2000

The native metastable fold of C1-inhibitor is stabilized by disulfide bonds.

C1-inhibitor is a member of the serpin family of proteinase inhibitors and is an important inhibitor of complement and contact system proteinases. The native protein has the characteristic serpin feature of being in a kinetically trapped metastable state rather than in the most stable state it could adopt. A consequence of this is that it readily forms loop-sheet dimers and polymers, by a mechanism believed to be the same as observed with other serpins. An unusual feature of C1-inhibitor is that it has a unique amino-terminal domain, of unknown function, held to the serpin domain by two disulfide bonds not found in other serpins. We report here that reduction of these bonds by DTT, causes a conformational change such that the reactive center loop inserts into beta-sheet A. This form of C1-inhibitor is less stable to heat and urea than the native protein, and is more susceptible to extensive degradation by trypsin. These data show that the disulfide bonds in C1-inhibitor are required for the protein to be stabilized in the metastable state with the reactive center loop expelled from beta-sheet A.

Binding Sites↗

PubMed2000

Enteropathogenic Escherichia coli dephosphorylates and dissociates occludin from intestinal epithelial tight junctions.

Enteropathogenic Escherichia coli (EPEC) increases tight junction permeability in part by phosphorylating the 20 kDa myosin light chain (MLC20) that induces cytoskeletal contraction. The impact of this enteric pathogen on specific tight junction (TJ) proteins has not been investigated. We examined the effect of EPEC infection on occludin localization and phosphorylation in intestinal epithelial cells. After infection by EPEC, a progressive shift of occludin from a primarily TJ-associated domain to an intracellular compartment occurred, as demonstrated by immunofluorescent staining. A reverse in the ratio of phosphorylated to dephosphorylated occludin accompanied this morphological change. Eradication of EPEC with gentamicin resulted in the normalization of occludin localization and phosphorylation. The serine/threonine phosphatase inhibitor, calyculin A, prevented these events. The EPEC-associated decrease in transepithelial electrical resistance, a measure of TJ barrier function, returned to baseline after gentamicin treatment. Non-pathogenic E. coli, K-12, did not induce these changes. Transformation of K-12 with the pathogenicity island of EPEC, however, conferred the phenotype of wild-type EPEC. Deletion of specific EPEC genes encoding proteins involved in EPEC type III secretion markedly attenuated these effects. These findings suggest that EPEC-induced alterations in occludin contribute to the pathophysiology associated with this infection.

Anti-Bacterial Agents↗

PubMed1979

Effect of milk on mercury absorption and gut retention in rats.

The retention of 203Hg was studied six days after a single oral or intraperitoneal administration to six week old female albino rats fed rat's diet or milk. After oral administration rats on milk diet had a two times higher retention of mercury in the gut-free carcass and a 23 times higher retention in the gut than animals on rat's diet. Changes in diet had very little influence on mercury retention after intraperitoneal administration. The higher gut and carcass rentions of mercury in animals on milk diet could be prevented or reduced by transferring rats from milk diet to rat's diet several days after an oral dose of mercury. These results might be relevant for interpreting high gut and carcass retention after oral administration of some metals in suckling and changes which occur at weaning.

Animals↗

PubMed1974