17 beta-estradiol-BSA conjugates and 17 beta-estradiol regulate growth plate chondrocytes by common membrane associated mechanisms involving PKC dependent and independent signal transduction

Nuclear receptors for 17 beta-estradiol (E(2)) are present in growth plate chondrocytes from both male and female rats and regulation of chondrocytes through these receptors has been studied for many years; however, recent studies indicate that an alternative pathway involving a membrane receptor may also be involved in the cell response. E(2) was found to directly affect the fluidity of chondrocyte membranes derived from female, but not male, rats. In addition, E(2) activates protein kinase C (PKC) in a nongenomic manner in female cells, and chelerythrine, a specific inhibitor of PKC, inhibits E(2)-dependent alkaline phosphatase activity and proteoglycan sulfation in these cells, indicating PKC is involved in the signal transduction mechanism. The aims of the present study were: (1) to examine the effect of a cell membrane-impermeable 17 beta-estradiol-bovine serum albumin conjugate (E(2)-BSA) on chondrocyte proliferation, differentiation, and matrix synthesis; (2) to determine the pathway that mediates the membrane effect of E(2)-BSA on PKC; and (3) to compare the action of E(2)-BSA to that of E(2). Confluent, fourth passage resting zone (RC) and growth zone (GC) chondrocytes from female rat costochondral cartilage were treated with 10(-9) to 10(-7) M E(2) or E(2)-BSA and changes in alkaline phosphatase specific activity, proteoglycan sulfation, and [(3)H]-thymidine incorporation measured. To examine the pathway of PKC activation, chondrocyte cultures were treated with E(2)-BSA in the presence or absence of GDP beta S (inhibitor of G-proteins), GTP gamma S (activator of G-proteins), U73122 or D609 (inhibitors of phospholipase C [PLC]), wortmannin (inhibitor of phospholipase D [PLD]) or LY294002 (inhibitor of phosphatidylinositol 3-kinase). E(2)-BSA mimicked the effects of E(2) on alkaline phosphatase specific activity and proteoglycan sulfation, causing dose-dependent increases in both RC and GC cell cultures. Both forms of estradiol inhibited [(3)H]-thymidine incorporation, and the effect was dose-dependent. E(2)-BSA caused time-dependent increases in PKC in RC and GC cells; effects were observed within three minutes in RC cells and within one minute in GC cells. Response to E(2) was more robust in RC cells, whereas in GC cells, E(2) and E(2)-BSA caused a comparable increase in PKC. GDP beta S inhibited the activation of PKC in E(2)-BSA-stimulated RC and GC cells. GTP gamma S increased PKC in E(2)-BSA-stimulated GC cells, but had no effect in E(2)-BSA-stimulated RC cells. The phosphatidylinositol-specific PLC inhibitor U73122 blocked E(2)-BSA-stimulated PKC activity in both RC and GC cells, whereas the phosphatidylcholine-specific PLC inhibitor D609 had no effect. Neither the PLD inhibitor wortmannin nor the phosphatidylinositol 3-kinase inhibitor LY294022 had any effect on E(2)-BSA-stimulated PKC activity in either RC or GC cells. The classical estrogen receptor antagonist ICI 182780 was unable to block the stimulatory effect of E(2)-BSA on PKC. Moreover, the classical receptor agonist diethylstilbestrol (DES) had no effect on PKC, nor did it alter the stimulatory effect of E(2)-BSA. The specificity of the membrane response to E(2) was also demonstrated by showing that the membrane receptor for 1 alpha,25-(OH)(2)D(3) was not involved. These data indicate that the rapid nongenomic effect of E(2)-BSA on PKC activity in RC and GC cells is dependent on G-protein-coupled PLC and support the hypothesis that many of the effects of E(2) involve membrane-associated mechanisms independent of classical estrogen receptors. (c) 2001 Wiley-Liss, Inc.     

Post-suspension hypotension is attenuated in Sprague-Dawley rats by prostacyclin synthase inhibition

Cardiovascular deconditioning, sometimes manifested in astronauts during standing postflight, may be related to the impairment of autonomic function and/or excessive production of endothelium-dependent relaxing factors. In the present study, we examined the cardiovascular responses to 7-day 30 degrees tail-suspension and a subsequent 6-h post-suspension period in conscious male Sprague-Dawley rats to determine the role of prostacyclin in the observed post-suspension reduction in mean arterial pressure (MAP). The specific prostacyclin synthase inhibitor U-51605 (0.3 mg/kg), or saline, was administered intravenously prior to release from suspension and at 2 and 4 h post-suspension. During 7 days of suspension, MAP did not change, however, there was a post-suspension reduction in MAP which was associated with significant increases in plasma prostacyclin and nitric oxide. U-51605 attenuated the observed post-suspension hypotension and reduced plasma prostacyclin levels, but not nitric oxide levels. The baroreflex sensitivity for heart rate was modified by U-51605: increased MAP threshold and effective MAP range. Thus, the post-suspension reduction in mean arterial pressure may be due to overproduction of prostacyclin and/or other endothelium-dependent relaxing factors and alteration in baroreflex activity.     

Na transport proteins are expressed by rat alveolar epithelial type I cells

Despite a presumptive role for type I (AT1) cells in alveolar epithelial transport, specific Na transporters have not previously been localized to these cells. To evaluate expression of Na transporters in AT1 cells, double labeling immunofluorescence microscopy was utilized in whole lung and in cytocentrifuged preparations of partially purified alveolar epithelial cells (AEC). Expression of Na pump subunit isoforms and the alpha-subunit of the rat (r) epithelial Na channel (alpha-ENaC) was evaluated in isolated AT1 cells identified by their immunoreactivity with AT1 cell-specific antibody markers (VIIIB2 and/or anti-aquaporin-5) and lack of reactivity with antibodies specific for AT2 cells (anti-surfactant protein A) or leukocytes (anti-leukocyte common antigen). Expression of the Na pump alpha(1)-subunit in AEC was assessed in situ. Na pump subunit isoform and alpha-rENaC expression was also evaluated by RT-PCR in highly purified (approximately 95%) AT1 cell preparations. Labeling of isolated AT1 cells with anti-alpha(1) and anti-beta(1) Na pump subunit and anti-alpha-rENaC antibodies was detected, while reactivity with anti-alpha(2) Na pump subunit antibody was absent. AT1 cells in situ were reactive with anti-alpha(1) Na pump subunit antibody. Na pump alpha(1)- and beta(1)- (but not alpha(2)-) subunits and alpha-rENaC were detected in highly purified AT1 cells by RT-PCR. These data demonstrate that AT1 cells express Na pump and Na channel proteins, supporting a role for AT1 cells in active transalveolar epithelial Na transport.     

Peroxisome senescence in human fibroblasts

The molecular mechanisms of peroxisome biogenesis have begun to emerge; in contrast, relatively little is known about how the organelle functions as cells age. In this report, we characterize age-related changes in peroxisomes of human cells. We show that aging compromises peroxisomal targeting signal 1 (PTS1) protein import, affecting in particular the critical antioxidant enzyme catalase. The number and appearance of peroxisomes are altered in these cells, and the organelles accumulate the PTS1-import receptor, Pex5p, on their membranes. Concomitantly, cells produce increasing amounts of the toxic metabolite hydrogen peroxide, and we present evidence that this increased load of reactive oxygen species may further reduce peroxisomal protein import and exacerbate the effects of aging.     

The scourge of scabies

Scabies ('Itch Mite') is truly a Great Neglected Disease that inflicts misery on millions. Molecular approaches, while still in their infancy, are providing a better understanding of the parasite and will have important implications for control and prevention. It has long been thought that dogs may act as a reservoir for human infections. However, genetic studies cast doubt over this supposition.     

Protein structure and import into the peroxisomal matrix

Proteins destined for the peroxisomal matrix are synthesized in the cytosol, and imported post-translationally. It has been previously demonstrated that stably folded proteins are substrates for peroxisomal import. Mammalian peroxisomes do not contain endogenous chaperone molecules. Therefore, it is possible that proteins are required to fold into their stable, tertiary conformation in order to be imported into the peroxisome. These investigations were undertaken to determine whether proteins rendered incapable of folding were also substrates for import into peroxisomes. Reduction of albumin resulted in a less compact tertiary structure as measured by analytical centrifugation. Microinjection of unfolded albumin molecules bearing the PTS1 targeting signal resulted in their import into peroxisomes. Kinetic analysis indicated that native and unfolded molecules were imported into peroxisomes at comparable rates. While import was unaffected by treatment with cycloheximide, hsc70 molecules were observed to be imported along with the unfolded albumin molecules. These results indicate that proteins, which are incapable of assuming their native conformation, are substrates for peroxisomal import. When combined with previous observations demonstrating the import of stably folded proteins, these results support the model that tertiary structure has no effect on protein import into the peroxisomal matrix .     

Reduced virulence caused by meiotic instability of the TOX2 chromosome of the maize pathogen Cochliobolus carbonum

The mechanisms by which pathogenic fungi evolve are poorly understood. Production of the host-selective cyclic peptide HC-toxin is controlled by a complex locus, TOX2, in the plant pathogen Cochliobolus carbonum. Crosses between toxin-producing (Tox2+) and toxin-nonproducing (Tox2-) isolates, as well as crosses between isolates in which the TOX2 genes were on chromosomes of different size, yielded progeny that had lost one or more copies of one or more of the TOX2 genes. Of approximately 200 progeny analyzed, eight (4%) had lost at least one TOX2 gene. All of them still had at least one functional copy of all of the known genes required for HC-toxin production (HTS1, TOXA, TOXC, and TOXE). Most deletion strains could be explained by simple chromosome breaks resulting in the loss of major contiguous portions (0.8 to 1.4 Mb) of the 3.5-Mb TOX2 chromosome, whereas others had more complicated patterns. All deletion strains had normal growth and were fertile, indicating that the 1.4 Mb of DNA contained no essential housekeeping genes. Most strains were also still virulent (Tox2+), but two had a novel phenotype of reduced virulence (RV), characterized by smaller lesions that expanded at a reduced rate and an inability to colonize plants systemically. Although the RV strains made no detectable HC-toxin in culture, the RV phenotype was dependent on the presence of a functional copy of HTS1, which encodes the central enzyme in HC-toxin biosynthesis. We propose that the RV strains still make a low level of HC-toxin, at least in planta, and that this is due to the loss of one or more genes that contribute to, but are not absolutely required for, HC-toxin synthesis.     

Novel approaches to the biosynthesis of vanillin

Microorganisms able to produce vanillin in excess of 6g/l from ferulic acid have now been isolated. In Pseudomonas strains, the metabolic pathway from eugenol via ferulic acid to vanillin has been characterised at the enzymic and molecular genetic levels. Attempts to introduce vanillin production into other organisms by genetic engineering have begun.