Betacellulin and amphiregulin induce upregulation of cyclin D1 and DNA synthesis activity through differential signaling pathways in vascular smooth muscle cells.

Activation of EGF receptors is closely involved in vascular proliferative diseases. The signaling mechanisms of EGF ligands, including betacellulin (BTC) and amphiregulin (AR), are poorly understood. We examined how BTC and AR induced DNA synthesis activity in primary cultures of human thoracic aortic smooth muscle cells (HTASMCs). BTC induced phosphorylation of all four EGF receptors present on HTASMCs: ErbB1, ErbB2, ErbB3, and ErbB4. BTC rapidly induced the phosphorylation of Akt, GSK3alpha/beta, and two FoxO factors, FKHR and AFX, in a dose- and time-dependent manner. BTC increased nuclear beta-catenin accumulation. BTC increased cyclin D1 mRNA, cyclin D1 protein, and DNA synthesis activity. Pretreatment with the phosphatidylinositol 3'-kinase (PI 3'-kinase) inhibitor wortmannin suppressed BTC-induced cyclin D1 mRNA and protein and DNA synthesis activity. In contrast, AR, a specific ErbB1 ligand, induced sustained ERK1/2 and Elk1 phosphorylation, increased cyclin D1 mRNA and protein, and increased DNA synthesis activity. AR did not produce any changes in Akt phosphorylation. Pretreatment with PD98059 suppressed AR-induced cyclin D1 mRNA and protein. Thus, the PI 3'-kinase/Akt/GSK/FoxO/beta-catenin pathway could be the major signaling cascade for BTC-induced upregulation of cyclin D1 protein, whereas a sustained ERK/Elk1 activation could be the major signaling cascade for AR-induced upregulation of cyclin D1 protein in HTASMCs. Moreover, immunohistochemical staining revealed that that BTC, ErbB1, and ErbB4 are upregulated in the plaques of human atherosclerotic coronary arteries. Taken together, BTC and AR could be potent growth factors in proliferative vascular diseases.

Betacellulin induces angiogenesis through activation of mitogen-activated protein kinase and phosphatidylinositol 3'-kinase in endothelial cell.

Betacellulin (BTC) is a member of the epidermal growth factor (EGF) family, and it acts through EGF receptors. We asked whether BTC could be an angiogenic factor. Using human umbilical vein endothelial cells (HUVECs), we examined the effect of BTC on kinases and angiogenic processes. BTC induced ERK1/2 and Akt phosphorylation in a dose- and time-dependent manner. BTC induced phosphorylation of all three EGF receptors present on HUVECs: ErbB2, ErbB3, and ErbB4. Pretreatment with effective concentrations of ErbB1 inhibitor did not suppress BTC-induced kinase phosphorylation. BTC, EGF, VEGF (all at 10 ng/ml) produced similar increases in DNA synthesis. BTC, EGF, and VEGF all significantly increased endothelial cell migration. In addition, BTC promoted survival in a dose-dependent manner, and its effect was inhibited by pretreatment with PtdIns 3'-kinase inhibitor wortmannin or MEK1/2 inhibitor PD98059. Both BTC and EGF produced similar increases in tube formation in collagen gels. BTC-induced tube formation was suppressed by PD98059, wortmannin, and LY294002. In the mouse Matrigel plug assay, BTC (100 ng/ml) promoted neovessel formation, and its effect was suppressed by a combination of wortmannin and PD98059. Taken together, these data show that BTC exerts potent angiogenic activity through activation of EGF receptors, mitogen-activated protein kinase, and PtdIns 3'-kinase/Akt in endothelial cells.

RANKL regulates endothelial cell survival through the phosphatidylinositol 3'-kinase/Akt signal transduction pathway.

The maintenance of endothelial integrity is important for prevention of vascular diseases. Several growth factors, such as bFGF and angiopoietin-1, have been shown to suppress endothelial cell apoptosis and thus help to maintain endothelial integrity. Several studies suggested that receptor activator of NF-kappaB (RANK) and its ligand (RANKL) could be involved in endothelial physiology. Using immunofluorescence and reverse transcriptase-polymerse chain reaction, we found that RANK was expressed by endothelial cells, and RANKL was expressed by arterial smooth muscle cells. Furthermore, RANKL suppressed apoptosis of primary cultured endothelial cells. The RANKL-induced survival appeared to be dependent on PI 3'-kinase activity, because wortmannin and LY294002, PI 3'-kinase-specific inhibitors, blocked the RANKL-induced survival effect. RANKL elicited the phosphorylation of the serine-threonine kinase Akt at Ser473 in a PI 3'-kinase-dependent manner. The expression of a dominant-negative form of Akt or pretreatment of Akt-specific inhibitor in endothelial cells reversed the RANKL-induced survival effect. Tumor necrosis factor-alpha, which causes endothelial cell apoptosis, induced endothelial cells to express osteoprotegerin, a decoy receptor that inhibits RANK-RANKL signaling. These findings indicate that RANK, in response to the paracrine stimulus of RANKL, may play an important role in maintaining endothelial cell integrity through the PI 3'-kinase/Akt signal transduction pathway.