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Biomedical subjects

Xiaoqiu Liu

Publications and source records attributed to Xiaoqiu Liu.

7 recordsLinked to original sources
PubMed2006

cAMP inhibits transforming growth factor-beta-stimulated collagen synthesis via inhibition of extracellular signal-regulated kinase 1/2 and Smad signaling in cardiac fibroblasts.

Cardiac fibroblasts produce and degrade extracellular matrix and are critical in regulating cardiac remodeling and hypertrophy. Cytokines such as transforming growth factor-beta (TGF-beta) play a fundamental role in the development of tissue fibrosis by stimulating matrix deposition and other profibrotic responses, but less is known about pathways that might inhibit fibrosis. Increased cAMP formation inhibits myofibroblast differentiation and collagen production by cardiac fibroblasts, but the mechanism of this inhibition is not known. We sought to characterize the signaling pathways by which cAMP-elevating agents alter collagen expression and myofibroblast differentiation. Treatment with 10 microM forskolin or isoproterenol increased cAMP production and cAMP response element binding protein (CREB) phosphorylation in cardiac fibroblasts and inhibited serum- or TGF-beta-stimulated collagen synthesis by 37% or more. These same cAMP-elevating agents blunted TGF-beta-stimulated expression of collagen I, collagen III, and alpha-smooth muscle actin. Forskolin or isoproterenol treatment blocked the activation of extracellular signal-regulated kinase 1/2 (ERK1/2) induced by TGF-beta despite the fact that these cAMP-elevating agents stimulated ERK1/2 activation on their own. cAMP-elevating agents also attenuated the activation of c-Jun NH(2)-terminal kinase and reduced binding of the transcriptional coactivator CREB-binding protein 1 to transcriptional complexes containing Smad2, Smad3, and Smad4. Pharmacological inhibition of ERK completely blocked TGF-beta-stimulated collagen gene expression, but expression of an active mutant of MEK was additive with TGF-beta treatment. Thus, cAMP-elevating agents inhibit the profibrotic effects of TGF-beta in cardiac fibroblasts largely through inhibiting ERK1/2 phosphorylation but also by reducing Smad-mediated recruitment of transcriptional coactivators.

Animals↗
PubMed2006

Cloning of transglutaminase gene from Streptomyces fradiae and its enhanced expression in the original strain.

The transglutaminase (TGase) gene of Streptomyces fradiae was cloned. It had an ORF of 1242 bp, encoding a presumed prepro-region of 82 amino acids and a mature TGase of 331 amino acids. Enhanced expression of the TGase was achieved by introducing another copy of TGase gene into the original host genome which was driven by the strong constitutive promoter, "ermE up", and shown to be expressed at the mRNA and protein levels. TGase activity in the recombinant strain (3.2 U/ml) was improved 1.3-fold when compared to that normally expressed in the original strain (2.4 U/ml). The specific enzyme activity in the recombinant strain (3.8 U/mg) was double that of the original strain (1.9 U/mg).

Amino Acid Sequence↗
PubMed2005

Fibrotic lung fibroblasts show blunted inhibition by cAMP due to deficient cAMP response element-binding protein phosphorylation.

Pulmonary fibroblasts regulate extracellular matrix production and degradation; thus, they are critical for maintenance of lung structure, function, and repair. In pulmonary fibrosis, fibroblasts produce excess collagen and form fibrotic foci that eventually impair lung function, but the mechanisms responsible for these alterations are not known. Receptors coupled to the stimulation of cAMP production can inhibit activation of fibroblasts and thereby are antifibrotic. To test whether this signaling pathway is altered in pulmonary fibrosis, we compared the ability of normal adult human pulmonary fibroblasts to generate and respond to cAMP with that of cells isolated from lungs with idiopathic pulmonary fibrosis. Serum- and transforming growth factor (TGF)-beta-stimulated cell proliferation was inhibited approximately 50% by forskolin and approximately 100% by prostaglandin (PG) E(2) in the normal cells but substantially less in the diseased cells. Collagen synthesis was also inhibited >50% by the same drugs in the normal cells but significantly less so in the diseased cells, despite responding with similar increases in cAMP production. Although expression of protein kinase A (PKA) and cAMP-stimulated PKA activity were similar in both the normal and diseased cell types, forskolin- and PGE(2)-stimulated cAMP response element-binding protein (CREB) phosphorylation was decreased in the diseased cell lines compared with the normal cells. cAMP-mediated activation and TGF-beta-mediated inhibition of CREB DNA binding was also diminished in the diseased cells. Thus, pulmonary fibroblasts derived from patients with pulmonary fibrosis are refractory to the inhibition by cAMP due to altered activity of components distal to the activity of PKA, in particular the phosphorylation of CREB.

Blotting, Western↗
PubMed2004

cAMP-elevating agents and adenylyl cyclase overexpression promote an antifibrotic phenotype in pulmonary fibroblasts.

Pulmonary fibroblasts are recruited to sites of lung injury, where they are activated to produce extracellular matrix proteins and to facilitate repair. However, these cells become dysregulated in pulmonary fibrosis, producing excess collagen at sites of injury and forming fibrotic loci that impair lung function. In this study, we used WI-38 human lung fibroblasts and evaluated the ability of G protein-coupled receptor agonists to increase cAMP production and regulate cell proliferation and collagen synthesis. WI-38 cells increase cAMP in response to the beta-adrenergic agonist isoproterenol (Iso), prostaglandin E(2) (PGE(2)), certain prostanoid receptor-selective agonists (beraprost, butaprost), an adenosine receptor agonist, and the direct adenylyl cyclase (AC) activator forskolin (Fsk). Responses to Iso, PGE(2), and Fsk were studied in more detail. Each induced a dose-dependent inhibition of serum-stimulated cell proliferation (as measured by [(3)H]thymidine incorporation) and collagen synthesis (as measured by [(3)H]proline incorporation, collagenase-sensitive [(3)H]proline incorporation, or levels of procollagen type 1 C-peptide). Quantitative RT-PCR analyses indicated that elevation in cellular cAMP levels decreases expression of collagen types 1alpha(II) and 5alpha(I) and increases expression and activity of matrix metalloproteinase 2 (MMP-2). Overexpression of AC type 6 or inhibition of cyclic nucleotide phosphodiesterases also increased cellular cAMP levels and decreased cell proliferation and collagen synthesis. Thus multiple approaches that increase cAMP signaling reduce proliferation and differentiated function in human pulmonary fibroblasts. These results suggest that therapies that raise cAMP levels may prove useful in the treatment of pulmonary fibrosis.

Adenylyl Cyclases↗
PubMed2002

Localization of adenylyl cyclase isoforms and G protein-coupled receptors in vascular smooth muscle cells: expression in caveolin-rich and noncaveolin domains.

A number of different agonists activate G protein-coupled receptors to stimulate adenylyl cyclase (AC), increase cAMP formation, and promote relaxation in vascular smooth muscle. To more fully understand this stimulation of AC, we assessed the expression, regulation, and compartmentation of AC isoforms in rat aortic smooth muscle cells (RASMC). Reverse transcription-polymerase chain reaction detected expression of AC3, AC5, and AC6 mRNA, whereas immunoblot analysis indicated expression of AC3 and AC5/6 protein primarily in caveolin-rich membrane (cav) fractions relative to noncaveolin (noncav) fractions. Beta(1)-adrenergic receptors (AR), beta(2)AR, and G(s) were detected in both cav and noncav fractions, whereas the prostanoid receptors EP(2)R and EP(4)R were excluded from cav fractions. We used an adenoviral construct to increase AC6 expression. Overexpressed AC6 localized only in noncav fractions. Two-fold overexpression of AC6 caused enhancement of forskolin-, isoproterenol- and prostaglandin E(2)-stimulated cAMP formation but no changes in basal levels of cAMP. At higher levels of AC6 overexpression, basal and adenosine receptor-stimulated cAMP levels were increased. Stimulation of cAMP levels by agents that increase Ca(2+) in native cells was consistent with the expression of AC3, but overexpression of AC6, which is inhibited by Ca(2+), blunted the Ca(2+)-stimulable cAMP response. These data indicate that: 1) RASMC express multiple AC isoforms that localize in both caveolin-rich and noncaveolin domains, 2) expression of AC6 in non-caveolin-rich membranes can increase basal levels of cAMP and response to several stimulatory agonists, and 3) Ca(2+)-mediated regulation of cAMP formation depends upon expression of different AC isoforms in RASMC. Compartmentation of GPCRs and AC is different in cardiomyocytes than in RASMC, indicating that targeting of these components to caveolin-rich membranes can be cell-specific. Moreover, our results imply that the colocalization of GPCRs and the AC isoforms they activate need not occur in caveolin-rich fractions.

Adenylyl Cyclases↗