Heparin inhibits mitogen-activated protein kinase activation in intact rat vascular smooth muscle cells

Heparin is potently antiproliferative for vascular smooth muscle cells in vivo and in vitro, inhibiting early proto-oncogene expression and blocking proliferation in the G1 phase of the cell cycle. The mitogen-activated protein kinase (MAPK) family of serine- and threonine-specific kinases is activated in response to a wide range of mitogenic and other factors and is a key intermediate in cell signaling. We found that heparin inhibits activation of MAPK in response to fetal calf serum and phorbol 12-myristate 13-acetate, but not epidermal growth factor, revealing heparin-sensitive and -insensitive pathways of MAPK activation. This report tentatively links suppression of early proto-oncogene expression and inhibition of cellular proliferation by heparin with inhibition of a mitogenically relevant kinase in living cells.