Molecular Cloning, Expression, and Characterization of Angiopoietin-related Protein

Abstract

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 NH₂-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 NH₂ terminus that is typical of a secretory signal sequence. Recombinant ARP2 expressed in COS cells is secreted and glycosylated. In human adult tissues, <i>ARP2</i> mRNA is most abundant in heart, small intestine, spleen, and stomach. In rat embryos, <i>ARP2</i> mRNA is most abundant in the blood vessels and skeletal muscles. Endothelial and vascular smooth muscle cells also contain <i>ARP2</i> 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.