Abstract
Atherosclerosis involves a specialized inflammatory process regulated by an intricate network of cytokine and chemokine signaling. Atherosclerotic lesions lead to the release of cytokines that can have multiple affects on various vascular cell functions either promoting lesion expansion or alternatively retard progression. Tumor necrosis factor-α (TNF-α) is one such cytokine that can activate both cell survival and cell death mechanisms simultaneously. Here we show that TNF-α induces apoptosis in human aortic endothelial cells (HAECs), while it promotes the proliferation of vascular smooth muscle cells (VSMCs). Both events involved the activation of the Rb-E2F1 transcriptional regulatory pathway. Stimulation of HAECs with TNF-α led to an increased expression of p73 protein and a reduction in the levels of p53. This involved apoptosis signal-regulating kinase 1 (ASK1)- mediated inactivation of Rb and its dissociation from the p73 promoter. In contrast, TNF-α stimulation of VSMCs enhanced the association of E2F1 with proliferative promoters like thymidylate synthase and cdc25A, while Rb was dissociated. ASK1 kinase has a critical role in the apoptotic process, as its depletion or dissociation from Rb reduced TNF-α-induced apoptosis. These results show that the cytokine TNF-α can elicit diametrically opposite responses in vascular endothelial cells and VSMCs, utilizing the Rb-E2F pathway.