Our previous study indicated that Thy-1, which is expressed on blood vessel endothelium in settings of pathological and a specific of physiological, but not during embryonic, angiogenesis, may be used as a marker for angiogenesis. However, the function of Thy-1 during angiogenesis is still not clear. Here, we demonstrate that knock-down of the endogenous Thy-1 expression by Thy-1 siRNA transfection promoted the migration of human umbilical vein endothelial cells (HUVEC). In contrast, treatment with interleukin-1β (IL-1β) or phorbol-12-myristate-13-acetate (PMA) increased the level of Thy-1 protein and reduced the migration of HUVEC. These effects were abolished by pre-transfection of HUVEC with Thy-1 siRNA to knock-down the expression of Thy-1. Moreover, over-expression of Thy-1 by transfection of HUVEC with Thy-1 pcDNA3.1 decreased the activity of RhoA and Rac-1 and inhibited the adhesion, migration and capillary-like tube formation of these cells. These effects were prevented by co-transfection of the cell with constitutively active RhoA construct (RhoA V14). On the other hand, pre-treatment with a ROCK (a kinase associated with RhoA for transducing RhoA signaling) inhibitor, Y27632, abolished the RhoA V14-induced prevention effect on the Thy-1-induced inhibition of endothelial cell migration and tube formation. Taken together, these results indicate that suppression of the RhoA-mediated pathway might participate in the Thy-1-induced migration inhibition in HUVEC. In the present study, we uncover a completely novel role of Thy-1 in endothelial cell behaviors.
We previously showed that overexpression of Thy-1 inhibited and knock-down of Thy-1 enhanced endothelial cell migration. Here, we used phorbol-12-myristate-13-acetate (PMA) as an inducer for Thy-1 expression to investigate molecular mechanisms underlying Thy-1 up-regulation. Our data showed that increased levels of Thy-1 mRNA and protein in endothelial cells were observed at 14–18 hours and 20–28 hours after PMA treatment, respectively. Treatment with PMA for 32 hours induced Thy-1 up-regulation and inhibited capillary-like tube formation and endothelial cell migration. These effects were abolished by Röttlerin (a PKC-δ inhibitor), but not Gö6976 (a PKC-α/β inhibitor). Moreover, pre-treatment with Bay 61–3606 (a Syk inhibitor) or Bay 11-7082 (a NF-κB inhibitor) abolished the PMA-induced Thy-1 up-regulation and migration inhibition in endothelial cells. Using the zebrafish model, we showed that PMA up-regulated Thy-1 and inhibited angiogenesis through the PKC-δ-mediated pathway. Surprisingly, we found that short-term (8–10 hours) PMA treatment enhanced endothelial cell migration. However, this effect was not observed in PMA-treated Thy-1-overexpressed endothelial cells. Taken together, our results suggest that PMA initially enhanced endothelial cell migration, subsequently activating the PKC-δ/Syk/NF-κB-mediated pathway to up-regulate Thy-1, which in turn inhibited endothelial cell migration. Our results also suggest that Thy-1 might play a role in termination of angiogenesis.
We previously showed that progesterone (P4) could inhibit the proliferation of human umbilical venous endothelial cells (HUVECs) through the p53-dependent pathway. In the present study, we further demonstrated that P4 at physiologic levels (5-500 nM) concentration-dependently inhibited migration of HUVECs. This effect was blocked by pre-treatment with the P4 receptor (PR) agonist-antagonist, RU486, suggesting that the P4-induced migration inhibition in HUVECs was through the PR-mediated signaling pathway. Western blot analyses demonstrated that the levels of RhoA and Rac-1 protein were reduced in the P4-treated HUVECs. P4 also inhibited the membrane translocation of RhoA and Rac-1 protein. Moreover, the P4-induced migration inhibition in HUVECs was prevented by over-expression of the constitutively active RhoA construct (RhoA V14). However, pre-treatment with the ROCK (a kinase associated with RhoA for transducing RhoA signaling) inhibitor, Y27632, abolished the over-expression of RhoA-induced prevention effect on the P4-induced migration inhibition in HUVECs. These data suggest that the inhibition of Rho GTPases might account for the P4-induced migration inhibition of HUVECs. Pre-treatment with the cSrc inhibitor, PP2, prevented the P4-induced migration inhibition in HUVEC. The levels of phosphorylated focal adhesion kinase (FAK) and paxillin protein were also decreased by P4 treatment. Taken together, these results suggest that suppression of the Rho-mediated pathway might be involved in the signal transduction leading to the inhibition of cell migration caused by P4 in HUVECs.
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