Growth factors downregulate vascular smooth muscle thromboxane receptors independent of cell growth
Dorn, G.W.; Becker, M.W.
American Journal of Physiology 262(4 Pt 1): C927-C933
1992
ISSN/ISBN: 0002-9513 PMID: 1533095 Document Number: 398438
Growth factors, in addition to being mitogenic, may modulate vascular smooth muscle differentiation. We tested whether serum or defined growth factors could regulate thromboxane A2 (TxA2) receptors in cultured rabbit aorta smooth muscle cells. Fetal bovine serum (10%) stimulated cell proliferation and DNA synthesis in subconfluent cell cultures. Binding of the thromboxane A2 agonist [1S-(1.alpha.2.beta.(5Z), 3.alpha.(1E/3S), 4.alpha.)]-7-[3-(3-hydroxy-4-p-iodophenoxy-1-butenyl)-7-oxabicyclo[2.2.1]heptan-2-yl]-5-heptenoic acid showed a 41% decrease in TxA2 receptors in cells treated with 10% serum compared with serum-deprived (0.1%) controls. Receptor downregulation by serum was gradually reversible upon serum withdrawal. Compared with serum-deprived cells, those exposed to 10% serum also had diminished TxA2-stimulated phosphatidylinositol hydrolysis. Regulatory actions of serum on TxA2 receptors were distinguished from mitogenic effects with heparin, which prevented cell growth but did not inhibited serum-induced downregulation of TxA2 receptors. Furthermore, low concentrations of platelet-derived growht factor and basic fibroblast growth factor decreased TxA2 receptors without stimulating cell proliferation or DNA synthesis. These observations describe a previously unrecognized regulatory action of growth factors on a vascular smooth muscle vasoconstrictor receptor, an action which is independent of effects of cell proliferation or DNA synthesis.