Molecular cloning and characterization of a novel angiopoietin family protein, angiopoietin-3.
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Using homology-based PCR, we have isolated cDNA encoding a novel member (491 amino acids) of the angiopoietin (Ang) family from human adult heart cDNA and have designated it angiopoietin-3 (Ang3). The NH2-terminal and COOH-terminal portions of Ang-3 contain the characteristic coiled-coil domain and fibrinogen-like domain that are conserved in other known Angs. Ang3 has a highly hydrophobic region at the N-terminus (approximately 21 amino acids) that is typical of a signal sequence for protein secretion. Ang3 mRNA is most abundant in adrenal gland, placenta, thyroid gland, heart and small intestine in human adult tissues. Additionally, Ang3 is a secretory protein, but is not a mitogen in endothelial cells. (+info)
Angiopoietins 3 and 4: diverging gene counterparts in mice and humans.
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The angiopoietins have recently joined the members of the vascular endothelial growth factor family as the only known growth factors largely specific for vascular endothelium. The angiopoietins include a naturally occurring agonist, angiopoietin-1, as well as a naturally occurring antagonist, angiopoietin-2, both of which act by means of the Tie2 receptor. We now report our attempts to use homology-based cloning approaches to identify new members of the angiopoietin family. These efforts have led to the identification of two new angiopoietins, angiopoietin-3 in mouse and angiopoietin-4 in human; we have also identified several more distantly related sequences that do not seem to be true angiopoietins, in that they do not bind to the Tie receptors. Although angiopoietin-3 and angiopoietin-4 are strikingly more structurally diverged from each other than are the mouse and human versions of angiopoietin-1 and angiopoietin-2, they appear to represent the mouse and human counterparts of the same gene locus, as revealed in our chromosomal localization studies of all of the angiopoietins in mouse and human. The structural divergence of angiopoietin-3 and angiopoietin-4 appears to underlie diverging functions of these counterparts. Angiopoietin-3 and angiopoietin-4 have very different distributions in their respective species, and angiopoietin-3 appears to act as an antagonist, whereas angiopoietin-4 appears to function as an agonist. (+info)
Angiopoietin-3, a novel member of the angiopoietin family.
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A cDNA clone encoding angiopoietin-3 protein (Ang3), a novel member of the angiopoietin family, was identified. Ang3 cDNA was cloned from a human aorta cDNA library. Ang3 is a 503 amino acid protein having 45.1% and 44.7% identity with human angiopoietin-1 and human angiopoietin-2, respectively. Ang3 mRNA is expressed in lung and cultured human umbilical vein endothelial cells (HUVECs). Ang3 mRNA expression in HUVECs was slightly decreased by vascular endothelial cell growth factor treatment, suggesting that the regulation of Ang3 mRNA expression is different from that of Ang2. (+info)
Molecular cloning, expression, and characterization of angiopoietin-related protein. angiopoietin-related protein induces endothelial cell sprouting.
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Using degenerate polymerase chain reaction, we isolated a cDNA encoding a novel 493-amino acid protein from human and mouse adult heart cDNAs and have designated it angiopoietin-related protein-2 (ARP2). The NH(2)-terminal and COOH-terminal portions of ARP2 contain the characteristic coiled-coil domain and fibrinogen-like domain that are conserved in angiopoietins. ARP2 has two consensus glycosylation sites and a highly hydrophobic region at the NH(2) terminus that is typical of a secretory signal sequence. Recombinant ARP2 expressed in COS cells is secreted and glycosylated. In human adult tissues, ARP2 mRNA is most abundant in heart, small intestine, spleen, and stomach. In rat embryos, ARP2 mRNA is most abundant in the blood vessels and skeletal muscles. Endothelial and vascular smooth muscle cells also contain ARP2 mRNA. Recombinant ARP2 protein induces sprouting in vascular endothelial cells but does not bind to the Tie1 or Tie2 receptor. These results suggest that ARP2 may exert a function on endothelial cells through autocrine or paracrine action. (+info)
Hepatic expression, synthesis and secretion of a novel fibrinogen/angiopoietin-related protein that prevents endothelial-cell apoptosis.
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Using degenerate PCR we isolated a cDNA encoding a novel 406- and 410-amino acid protein from human and mouse embryonic cDNAs and have designated it 'hepatic fibrinogen/angiopoietin-related protein' (HFARP). The N-terminal and C-terminal portions of HFARP contain the characteristic coiled-coil domains and fibrinogen-like domains that are conserved in angiopoietins. In human and mouse tissues, HFARP mRNA is specifically expressed in the liver. HFARP mRNA and protein are mainly present in the hepatocytes. HFARP has a highly hydrophobic region at the N-terminus that is typical of a secretory signal sequence and one consensus glycosylation site. Recombinant HFARP expressed in COS-7 cells is secreted and glycosylated. HFARP protein is present not only in the hepatocytes, but also in the circulating blood. Recombinant HFARP acts as an apoptosis survival factor for vascular endothelial cells, but does not bind to Tie1 or Tie2 (endothelial-cell tyrosine kinase receptors). These results suggest that HFARP may exert a protective function on endothelial cells through an endocrine action. (+info)
Expression of Tie1, Tie2, and angiopoietins 1, 2, and 4 in Kaposi's sarcoma and cutaneous angiosarcoma.
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The angiopoietins are recently described growth factors for vascular endothelium. The Tie1 and Tie2 receptors are expressed by endothelium. Acquired immune deficiency syndrome (AIDS)-associated Kaposi's sarcoma (KS) and cutaneous angiosarcoma are malignancies of endothelial origin. KS involves primarily the skin and mucosal surfaces and is common in AIDS patients. In an effort to determine whether the angiopoietins and Tie receptors play a role in the pathobiology of angiosarcoma and KS, we studied the expression of angiopoietin-1, angiopoietin-2, angiopoietin-4, Tie1, and Tie2 mRNAs in biopsies of KS from 12 AIDS patients, in biopsies of cutaneous angiosarcoma from two patients, and in control biopsies of normal skin from three volunteers by in situ hybridization. Strong expression of angiopoietin-2, Tie1, and Tie2 mRNAs was detected in the tumor cells of KS and cutaneous angiosarcomas, in contrast to the focal low-level expression in normal skin biopsies. Focal low-level expression of angiopoietin-1 was seen in KS, cutaneous angiosarcomas, and in normal skin. Focal low-level expression of angiopoietin-4 was identified in a minority of KS lesions. These findings suggest that the angiopoietins and Tie receptors may play an important role in the pathobiology of KS and cutaneous angiosarcoma and identify additional potential targets for therapeutic intervention in these vascular malignancies. (+info)
Characterization of the fasting-induced adipose factor FIAF, a novel peroxisome proliferator-activated receptor target gene.
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Fasting is associated with significant changes in nutrient metabolism, many of which are governed by transcription factors that regulate the expression of rate-limiting enzymes. One factor that plays an important role in the metabolic response to fasting is the peroxisome proliferator-activated receptor alpha (PPARalpha). To gain more insight into the role of PPARalpha during fasting, and into the regulation of metabolism during fasting in general, a search for unknown PPARalpha target genes was performed. Using subtractive hybridization (SABRE) comparing liver mRNA from wild-type and PPARalpha null mice, we isolated a novel PPARalpha target gene, encoding the secreted protein FIAF (for fasting induced adipose factor), that belongs to the family of fibrinogen/angiopoietin-like proteins. FIAF is predominantly expressed in adipose tissue and is strongly up-regulated by fasting in white adipose tissue and liver. Moreover, FIAF mRNA is decreased in white adipose tissue of PPARgamma +/- mice. FIAF protein can be detected in various tissues and in blood plasma, suggesting that FIAF has an endocrine function. Its plasma abundance is increased by fasting and decreased by chronic high fat feeding. The data suggest that FIAF represents a novel endocrine signal involved in the regulation of metabolism, especially under fasting conditions. (+info)
Peroxisome proliferator-activated receptor gamma target gene encoding a novel angiopoietin-related protein associated with adipose differentiation.
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The nuclear receptor peroxisome proliferator-activated receptor gamma regulates adipose differentiation and systemic insulin signaling via ligand-dependent transcriptional activation of target genes. However, the identities of the biologically relevant target genes are largely unknown. Here we describe the isolation and characterization of a novel target gene induced by PPARgamma ligands, termed PGAR (for PPARgamma angiopoietin related), which encodes a novel member of the angiopoietin family of secreted proteins. The transcriptional induction of PGAR follows a rapid time course typical of immediate-early genes and occurs in the absence of protein synthesis. The expression of PGAR is predominantly localized to adipose tissues and placenta and is consistently elevated in genetic models of obesity. Hormone-dependent adipocyte differentiation coincides with a dramatic early induction of the PGAR transcript. Alterations in nutrition and leptin administration are found to modulate the PGAR expression in vivo. Taken together, these data suggest a possible role for PGAR in the regulation of systemic lipid metabolism or glucose homeostasis. (+info)