Growth Factors Produced By Cultured Human Vascular Endothelial Cells

Abstract

The growth of cells in culture is regulated by several as yet undefined growth factors which are normally present in serum and released by cultured cells in vitro. We have investigated media conditioned by cultured vascular human endothelial cells (HEC) and smooth muscle cells (SMC) derived from umbilical veins and expiants from umbilical cords respectively. Cell proliferation was measured by 3H thymidine uptake. The conditioned medium of confluent endothelial cells (HECS) contain(s) oneor more factors which inhibit the growth of nonconfluent endothelial cells and SMC. HECS derived from actively growing HEC as well as conditioned SMC medium were inactive. The growth factor(s) is (are) also present in serum free HECS and is released in a time dependant fashion at least up to 72 h. The release of HECS does not correlate with cell lysis, but our experiments indicate that protein synthesis is required for the generation of HECS. HECS contains also potent growth factor(s) for hybridoma cells particularly for xenogenetic hybridomas between mouse myeloma cells and human lymphocytes. HECS can substitute for feeder cells in cloning by limiting dilution of hybridoma cells. The growth of hybridoma cells is enhanced, both by a 24 h “pulse” with HEC as well as in its continuous presence during culture, indicating that the effect is based on delivering a growth signal to the cells. In preliminary experiments to characterize HECS, the following findings were observed, - HECS production requires protein synthesis in endothelial cells, - the activity is abolished by treatment with periodate, suggesting that sugar moieties are involved, - on gel filtration HECS activity is associated with a molecular weight of 20-30×103. These findings demonstrate that one or more growth factors are synthesized and released by vascular endothelial cells, a finding which underlines once more the pivotal role of the endothelium in biological systems.