Signal transduction of betacellulin in growth and migration of vascular smooth muscle cells

Epidermal growth factor (EGF) family ligands have been implicated in cardiovascular diseases because of their enhanced expression in vascular lesions and their promoting effects on growth and migration of vascular smooth muscle cells (VSMCs). Betacellulin (BTC), a novel EGF family ligand, has been shown to be expressed in atherosclerotic lesions and to be a potent growth factor of VSMCs. However, the molecular mechanisms downstream of BTC involved in mediating vascular remodeling remain largely unknown. Therefore, the aim of this study was to examine the effects of BTC on signal transduction, growth, and migration in VSMCs. We found that BTC stimulated phosphorylation of EGF receptor ( EGFR) at Tyr1068, which was completely blocked by an EGFR kinase inhibitor, AG-1478. BTC also phosphorylated ErbB2 at Tyr877, Tyr1112, and Tyr1248 and induced association of ErbB2 with EGFR, suggesting their heterodimerization in VSMCs. In post-receptor signal transduction, BTC stimulated phosphorylation of extracellular signal-regulated kinase (ERK) 1/2, Akt, and p38 mitogen-activated protein kinase ( MAPK). Moreover, BTC stimulated proliferation and migration of VSMCs. ERK and Akt inhibitors suppressed migration markedly and proliferation partially, whereas the p38 inhibitor suppressed migration partially but not proliferation. In addition, we found the presence of endogenous BTC in conditioned medium of VSMCs and an increase of BTC on angiotensin II stimulation. In summary, BTC promotes growth and migration of VSMCs through activation of EGFR, ErbB2, and downstream serine/ threonine kinases. Together with the expression and processing of endogenous BTC in VSMCs, our results suggest a critical involvement of BTC in vascular remodeling.