RnoEX0009290 @ rn6

Angiopoietin-1 (Ang-1) is required for developing vessels, and its absence leads to defects in vessel remodeling. Ang-1 has been identified as the ligand for the tyrosine kinase receptor Tie-2, which is expressed specifically on endothelial cells and early hematopoietic cells. In studying the role of Tie-2 and Ang-1 in megakaryocytopoiesis, 3 alternatively spliced species of Ang-1 mRNA (Ang-1.3 kb, Ang-0.9 kb, and Ang-0.7 kb) were identified in addition to the full-length Ang-1 (Ang-1.5 kb), in the megakaryocyte cell line CHRF by reverse transcription?polymerase chain reaction (RT-PCR), and then cloned and sequenced. The function of the 1.5-kb (contains exon encoding fibronogen C-terminal domain (HsaEX0004096)), 1.3-kb (lacks aforementioned exon), and 0.9-kb (contains the aforementioned exon) isoforms was examined. Recombinant proteins Ang-1.5 and 0.9 kb bind strongly to the recombinant Tie-2 receptor (Tie-2-Fc), whereas the 1.3-kb isoform does not. The Ang-1.3 kb isoform binds to the 1.5-kb isoform. Ang-1.5 kb, but not the 1.3-kb and 0.9-kb isoforms, induces tyrosine phosphorylation of Tie-2 in human umbilical vein endothelial cells. These data suggest that isoforms 1.3 kb and 0.9 kb could serve as dominant negative molecules for the full-length Ang-1. Of note, the only difference between the 1.5-kb and 1.3-kb isoforms is the presence/absence of the exon encoding the fibronogen C-terminal domain (HsaEX0004096).