Insulin up-regulates a Glc3Man9GlcNAc2-PP-Dol pool in capillary endothelial cells not essential for angiogenesis.

Endothelial cells line blood vessels, and their proliferation during neovascularization ( i.e., angiogenesis) is essential for a normal growth and development as well as for tumor progression and metastasis. Mechanistic details indicated that down-regulation of Glc(3)Man(9)GlcNAc(2)-PP-Dol level reduced angiogenesis and induced apoptosis in capillary endothelial cells (Martínez JA, Torres-Negrón I, Amigó LA, Banerjee DK, Cellular and Molec Biochem 45, 137-152 (1999)). Unlike in any other insulin-responsive cells, insulin reduced capillary endothelial cell proliferation by increasing the cell doubling time. But, when analyzed, the rate of lipid-linked oligosaccharide-PP-Dol (LLO) synthesis as well as its turnover ( i.e., t(1/2)) were increased in insulin treated cells. No major differences in their molecular size were observed. This corroborated with an enhanced glycosylation of Factor VIIIC, an N-linked glycoprotein (essential cofactor of the blood coagulation cascade) and a marker for the capillary endothelial cell. Increased LLO synthesis was independent of elevating either Dol-P level or Man-P-Dol synthase gene (dpm) transcription. Insulin however, enhanced 2-deoxy-glucose transport across the endothelial cell plasma membrane and caused increased secretion of Factor VIIIC, thus, supporting the existence of additional LLO pool(s), and arguing favorably that growth retardation of capillary endothelial cells by insulin turned a highly proliferative cell into a highly secretory cell.