Biomedical subjects

S Sandefur

Publications and source records attributed to S Sandefur.

5 recordsLinked to original sources

PubMed1998

Collagenase-3 induction in rat lung fibroblasts requires the combined effects of tumor necrosis factor-alpha and 12-lipoxygenase metabolites: a model of macrophage-induced, fibroblast-driven extracellular matrix remodeling during inflammatory lung injury.

The mechanisms responsible for the induction of matrix-degrading proteases during lung injury are ill defined. Macrophage-derived mediators are believed to play a role in regulating synthesis and turnover of extracellular matrix at sites of inflammation. We find a localized increase in the expression of the rat interstitial collagenase (MMP-13; collagenase-3) gene from fibroblastic cells directly adjacent to macrophages within silicotic rat lung granulomas. Conditioned medium from macrophages isolated from silicotic rat lungs was found to induce rat lung fibroblast interstitial collagenase gene expression. Conditioned medium from primary rat lung macrophages or J774 monocytic cells activated by particulates in vitro also induced interstitial collagenase gene expression. Tumor necrosis factor-alpha (TNF-alpha) alone did not induce interstitial collagenase expression in rat lung fibroblasts but did in rat skin fibroblasts, revealing tissue specificity in the regulation of this gene. The activity of the conditioned medium was found to be dependent on the combined effects of TNF-alpha and 12-lipoxygenase-derived arachidonic acid metabolites. The fibroblast response to this conditioned medium was dependent on de novo protein synthesis and involved the induction of nuclear activator protein-1 activity. These data reveal a novel requirement for macrophage-derived 12-lipoxygenase metabolites in lung fibroblast MMP induction and provide a mechanism for the induction of resident cell MMP gene expression during inflammatory lung processes.

Animals↗

PubMed1998

The I domain is required for efficient plasma membrane binding of human immunodeficiency virus type 1 Pr55Gag.

The interaction of the human immunodeficiency virus type 1 (HIV-1) Pr55Gag molecule with the plasma membrane of an infected cell is an essential step of the viral life cycle. Myristic acid and positively charged residues within the N-terminal portion of MA constitute the membrane-binding domain of Pr55Gag. A separate assembly domain, termed the interaction (I) domain, is located nearer the C-terminal end of the molecule. The I domain is required for production of dense retroviral particles, but has not previously been described to influence the efficiency of membrane binding or the subcellular distribution of Gag. This study used a series of Gag-green fluorescent protein fusion constructs to define a region outside of MA which determines efficient plasma membrane interaction. This function was mapped to the nucleocapsid (NC) region of Gag. The minimal region in a series of C-terminally truncated Gag proteins conferring plasma membrane fluorescence was identified as the N-terminal 14 amino acids of NC. This same region was sufficient to create a density shift in released retrovirus-like particles from 1.13 to 1.17 g/ml. The functional assembly domain previously termed the I domain is thus required for the efficient plasma membrane binding of Gag, in addition to its role in determining the density of released particles. We propose a model in which the I domain facilitates the interaction of the N-terminal membrane-binding domain of Pr55Gag with the plasma membrane.

Amino Acid Sequence↗

PubMed1996

Monocytic cell type-specific transcriptional induction of collagenase.

Interstitial collagenase (MMP-1), a metalloproteinase produced by resident and inflammatory cells during connective tissue turnover, cleaves type I collagen fibrils. This catalytic event is rate limiting in remodeling of tissues rich in fibrillar collagen such as the skin and lungs. The regulation of collagenase expression is cell-type specific; bacterial LPS and zymosan, a yeast cell wall derivative, are potent inducers of collagenase expression in macrophages, but do not alter fibroblast collagenase expression. Since promoter elements controlling collagenase transcription in monocytic cells have not been previously defined, we sought to delineate responsive cis-acting elements of the collagenase promoter in transiently transfected human (U937) and murine (J774) monocytic cell lines. Deletion constructs containing as little as 72 bp of 5' -flanking sequence of the collagenase promoter were sufficient for LPS- or zymosan-mediated transcriptional induction, whereas phorbol inducibility exhibited an absolute requirement for upstream elements including the polyoma enhancer A-binding protein-3 site (-83 to -91) and TTCA sequence (-102 to -105) in both monocytic cells and fibroblasts. Mutagenesis of the activator protein-1 [AP-1] site at -72 abolished basal promoter activity and LPS/zymosan inducibility, while mutagenesis of an NF-kappaB-like site at -20 to -10 had no effect. Nuclear extracts from LPS- and zymosan-treated cells showed strong AP-1 activity by gel-shift analysis, and supershift analysis showed the AP-1 complexes contained specific members of both the jun and fos gene families. These data indicate that, in contrast to most LPS effects, AP-1, but not nuclear factor-kappaB, mediates LPS induction of collagenase transcription in macrophagelike cells. Furthermore, as compared to regulation by phorbol ester, collagenase induction in monocytic cells by cell wall derivatives of bacteria or yeast is largely independent of upstream promoter sequences.

Animals↗

PubMed1995

Glucocorticoids upregulate tropoelastin expression during late stages of fetal lung development.

The production of elastin, an essential extracellular matrix protein of terminal airway interstitium, occurs mostly during early development. Because glucocorticoids influence airway maturation, we studied the effect of dexamethasone (Dex) on tropoelastin expression during fetal lung development. Timed-pregnant rats were treated with Dex (1 mg/kg daily), and fetal lungs were collected 3 days later at 17, 19, and 21 days of gestation. Dex treatment resulted in about a threefold increase in tropoelastin mRNA levels at 19 days concomitant with accelerated airway development. By in situ hybridization, Dex treatment increased the number of tropoelastin-expressing cells and the level of tropoelastin mRNA per cell. In organ culture, Dex increased lung tropoelastin expression and augmented cortisol stimulation of tropoelastin expression. In fetal pulmonary artery smooth muscle cells, 10(-8) M Dex upregulated tropoelastin mRNA expression and increased tropoelastin promoter-chloramphenicol acetyl transferase activity in transient transfections. These data indicate that pharmacologically administered glucocorticoids transcriptionally upregulate fetal lung tropoelastin expression and suggest that steroid hormones may be important regulators of elastin production in vivo.

Animals↗

PubMedDate not supplied

Elastin in lung development.

Elastin is a critical component of the lung interstitium, providing the property of recoil to the vascular, conducting airway, and terminal airspace compartments of the lung. Elastic fibers, consisting of soluble tropoelastin monomers cross-linked on a preexisting scaffold of microfibrils, are produced primarily during late fetal and neonatal stages of development. The factors and molecular mechanisms regulating the cell type-specific and tightly temporally regulated expression of tropoelastin are currently under investigation. The onset and inductive phase of tropoelastin expression are characterized by increased transcription of the tropoelastin gene. Glucocorticoids accelerate this induction in fetal rats during the canalicular stage of lung development. Many additional factors regulate tropoelastin expression in cultured lung fibroblasts and vascular smooth muscle cells, but the in vivo roles of such mediators are still under investigation. Cell-cell interactions may also promote elastogenesis during lung development, as localization of tropoelastin mRNA in pseudo-glandular and canalicular lungs demonstrates a close spatial relationship between epithelium and adjacent elastogenic mesenchyme. Elastin metabolism is altered in several experimental models of bronchopulmonary dysplasia, characterized by abnormal lung morphological development, suggesting that normal elastin production and deposition is necessary for proper development of alveoli. Studies employing reverse genetics may prove useful in further defining the role of elastin in lung development.

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