Angiogenic oligosaccharides of hyaluronan induce multiple signaling pathways affecting vascular endothelial cell mitogenic and wound healing responses

Abstract

Hyaluronan (HA) is a large nonsulfated glycosaminoglycan and an important regulator of angiogenesis, in particular, the growth and migration of vascular endothelial cells. We have identified some of the key intermediates responsible for induction of mitogenesis and wound recovery. Treatment of bovine aortic endothelial cells with oligosaccharides of hyaluronan (o-HA) resulted in rapid tyrosine phosphorylation and plasma membrane translocation of phospholipase Cγ1 (PLCγ1). Cytoplasmic loading with inhibitory antibodies to PLCγ1, Gβ, and Gαi/o/t/z inhibited activation of extracellular-regulated kinase 1/2 (ERK1/2). Treatment with the Gαi/o inhibitor, pertussis toxin, reduced o-HA-induced PLCγ1 tyrosine phosphorylation, protein kinase C (PKC) α and β1/2 membrane translocation, ERK1/2 activation, mitogenesis, and wound recovery, suggesting a mechanism for o-HA-induced angiogenesis through G-proteins, PLCγ1, and PKC. In particular, we demonstrated a possible role for PKCα in mitogenesis and PKCβ1/2 in wound recovery. Using antisense oligonucleotides and the Ras farnesylation inhibitor FTI-277, we showed that o-HA-induced bovine aortic endothelial cell proliferation, wound recovery, and ERK1/2 activation were also partially dependent on Ras activation, and that o-HA-stimulated tyrosine phosphorylation of the adapter protein Shc, as well as its association with Sos1. Binding of Src to Shc was required for its activation and for Ras-dependent activation of ERK1/2, cell proliferation, and wound recovery. Neither Src nor Ras activation was inhibited by pertussis toxin, suggesting that their activation was independent of heterotrimeric G-proteins. However, the specific Src kinase inhibitor PP2 inhibited Gβ subunit co-precipitation with PLCγ1, suggesting a possible role for Src in activation of PLCγ1 and interaction between two distinct o-HA-induced signaling pathways.