Matrix GLA protein modulates branching morphogenesis in fetal rat lung

Gilbert, Kirk A.; Rannels, Stephen R.

doi:10.1152/ajplung.00188.2003

Cited by 27 publications

(21 citation statements)

References 49 publications

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“…5B). We also found that Habc-EPM and Habc132 increased gene expression of a number of additional transcripts encoding molecules known to be involved in branching morphogenesis, including Fas (31) and matrix GLA protein (32) (Fig. 5B).…”

Section: Resultsmentioning

confidence: 62%

Homology with Vesicle Fusion Mediator Syntaxin-1a Predicts Determinants of Epimorphin/Syntaxin-2 Function in Mammary Epithelial Morphogenesis

Chen

Nelson

Khauv

et al. 2009

Journal of Biological Chemistry

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We have shown that branching morphogenesis of mammary ductal structures requires the action of the morphogen epimorphin/syntaxin-2. Epimorphin, originally identified as an extracellular molecule, is identical to syntaxin-2, an intracellular molecule that is a member of the extensively investigated syntaxin family of proteins that mediate vesicle trafficking. We show here that, although epimorphin/syntaxin-2 is highly homologous to syntaxin-1a, only epimorphin/syntaxin-2 can stimulate mammary branching morphogenesis. We construct a homology model of epimorphin/syntaxin-2 based on the published structure of syntaxin-1a, and we use this model to identify the structural motif responsible for the morphogenic activity. We identify four residues located within the cleft between helices B and C that differ between syntaxin-1a and epimorphin/syntaxin-2; through site-directed mutagenesis of these four amino acids, we confer the properties of epimorphin for cell adhesion, gene activation, and branching morphogenesis onto the inactive syntaxin-1a template. These results provide a dramatic demonstration of the use of structural information about one molecule to define a functional motif of a second molecule that is related at the sequence level but highly divergent functionally.Branching morphogenesis is a developmental process involved in the formation of many organs, including mammary gland, lung, kidney, and salivary gland. In the mammary gland, branching morphogenesis allows the primitive anlage to develop into the highly ramified mammary ductal tree. Investigations of the signaling processes involved in mammary ductal branching have revealed that branching requires the presence of a growth factor and the morphogen epimorphin (1). Epimorphin binds to mammary epithelial cells through ␣v-integrins (2), activating morphogenic processes that are dependent upon the transcription factor CCAAT/enhancer-binding protein-␤ (C/EBP␤) 5 (3), and mediating branching and invasion into the extracellular matrix through activation of matrix metalloproteinase-3 (MMP3) (4). Although epimorphin is required for branching morphogenic processes, overexpression of epimorphin can lead to pathological consequences, including ductal hyperplasia and mammary cancer (3, 5). Epimorphin plays a role in morphogenesis of other epithelial organs as well, including kidney (6), pancreas (7,8), hair (9), intestine (10, 11), and lung (12).Although epimorphin was first identified as an extracellular morphogen through the use of function-blocking antibodies in lung and skin organ culture assays (12, 13), the same molecule was later found to function in the cytoplasm as syntaxin-2, a member of the syntaxin family of proteins that controls vesicle fusion (14, 15). However, the idea that epimorphin/syntaxin-2 might have distinct roles dependent upon its location on the outside or inside of the plasma membrane is controversial (14 -16), in part because epimorphin lacks a canonical peptide signal sequence to direct extracellular localization through the ER/Golgi path...

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Section: Resultsmentioning

confidence: 62%

Homology with Vesicle Fusion Mediator Syntaxin-1a Predicts Determinants of Epimorphin/Syntaxin-2 Function in Mammary Epithelial Morphogenesis

Chen

Nelson

Khauv

et al. 2009

Journal of Biological Chemistry

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“…Pulmonary expression of MGP starts to increase after E14 (20), which coincides with an exponential increase in vascular networks (21). To examine if a branching defect led to the abnormal vasculature in the MGP transgenics, we examined the pulmonary vessels in non-perfused E15.5 and E18.5 embryos.…”

Section: Resultsmentioning

confidence: 99%

Matrix GLA Protein, an Inhibitory Morphogen in Pulmonary Vascular Development

Yao

Nowak

Yochelis

et al. 2007

Journal of Biological Chemistry

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Deficiency of matrix GLA protein (MGP), an inhibitor of bone morphogenetic protein (BMP)-2/4, is known to cause arterial calcification and peripheral pulmonary artery stenosis. Yet the vascular role of MGP remains poorly understood. To further investigate MGP, we created a new MGP transgenic mouse model with high expression of the transgene in the lungs. The excess MGP led to a disruption of the pulmonary pattern of BMP-4, and resulted in significant morphological defects in the pulmonary artery tree. Specifically, the vascular branching pattern lacked characteristic side branching, whereas control lungs had extensive side branching accounting for as much as 40% of the vascular endothelium. The vascular changes could be explained by a dramatic reduction of phosphorylated SMAD1/ 5/8 in the alveolar epithelium, and in epithelial expression of the activin-like kinase receptor 1 and vascular endothelial growth factor, both critical in vascular formation. Abnormalities were also found in the terminal airways and in lung cell differentiation; high levels of surfactant protein-B were distributed in an abnormal pattern suggesting lost coordination between vasculature and airways. Ex vivo, lung cells from MGP transgenic mice showed higher proliferation, in particular surfactant protein B-expressing cells, and conditioned medium from these cells poorly supported in vitro angiogenesis compared with normal lung cells. The vascular branching defect can be mechanistically explained by a computational model based on activator/inhibitor reaction-diffusion dynamics, where BMP-4 and MGP are considered as an activating and inhibitory morphogen, respectively, suggesting that morphogen interactions are important for vascular branching. Matrix GLA protein (MGP)2 is a known inhibitor of vascular calcification. Lack of MGP causes arterial calcification in mice (1) and the human Keutel syndrome, which is due to mutations in the MGP gene (2). The arterial calcification in mice is associated with profound changes in cell differentiation as arterial smooth muscle cells are replaced by chondrocytelike cells undergoing progressive mineralization (1). MGP deficiency also causes peripheral pulmonary artery stenosis and other morphological defects, including nasal hypoplasia and abnormal cartilage and bone calcification (2, 3). Furthermore, alterations in MGP expression has been reported in various tumors including a loss of MGP during progression of lung and colorectal carcinomas (4, 5), which may be related to tumor vascularization given that differential MGP expression has been observed in endothelial cells during angiogenesis (6).Previous work by our group and others has suggested that MGP can act as an inhibitory morphogen, acting antagonistically to bone morphogenetic proteins (BMP)-2 and -4 (7-9). Our previous studies also showed close links between BMP-4, MGP, the activin-like kinase receptor 1 (ALK1), a transforming growth factor (TGF)-␤ receptor essential in vascular formation, and vascular endothelial growth factor (VEGF) (9). BMP-4 ...

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“…MGP expression is observed throughout lung morphogenesis. It has been localized to the submucosal layers in the developing respiratory tract in mice (57), and has been associated with lung branching (58,59). TGF-␤ and VEGF are both involved in the development and maintenance of lungs (10,60), where correct spatial and timely expression of TGF-␤, TGF-␤ receptors, and VEGF is crucial for morphogenesis.…”

Section: Figmentioning

confidence: 99%