HIV-1 Tat protein-induced VCAM-1 expression in human pulmonary artery endothelial cells and its signaling

Expression of cell adhesion molecule in endothelial cells upon activation by human immunodeficiency virus (HIV) infection is associated with the development of atherosclerotic vasculopathy. We postulated that induction of vascular cell adhesion molecule-1 (VCAM-1) by HIV-1 Tat protein in endothelial cells might represent an early event that could culminate in inflammatory cell recruitment and vascular injury. We determined the role of HIV-1 Tat protein in VCAM-1 expression in human pulmonary artery endothelial cells (HPAEC). HIV-1 Tat protein treatment significantly increased cell-surface expression of VCAM-1 in HPAEC. Consistently, mRNA expression of VCAM-1 was also increased by HIV-1 Tat protein as measured by RT-PCR. HIV-1 Tat protein-induced VCAM-1 expression was abolished by the NF-kappaB inhibitor pyrrolidine dithiocarbamate (PDTC) and the p38 MAPK inhibitor SB-203580. Furthermore, HIV-1 Tat protein enhanced DNA binding activity of NF-kappaB, facilitated nuclear translocation of NF-kappaB subunit p65, and increased production of reactive oxygen species (ROS). Similarly to VCAM-1 expression, HIV-1 Tat protein-induced NF-kappaB activation and ROS generation were abrogated by PDTC and SB-203580. These data indicate that HIV-1 Tat protein is able to induce VCAM-1 expression in HPAEC, which may represent a pivotal early molecular event in HIV-induced vascular/pulmonary injury. These data also suggest that the molecular mechanism underlying the HIV-1 Tat protein-induced VCAM-1 expression may involve ROS generation, p38 MAPK activation, and NF-kappaB translocation, which are the characteristics of pulmonary endothelial cell activation.     

CD40-mediated activation of vascular smooth muscle cell chemokine production through a Src-initiated, MAPK-dependent pathway

The interaction between CD40 ligand (CD154) expressed on activated T cells and its receptor, CD40, has been shown to play a role in the onset and maintenance of autoimmune inflammation. Recent studies suggest that CD154+T cells also contribute to the regulation of atherogenesis due to their capacity to activate CD40+cells of the vasculature, including vascular smooth muscle cells (VSMC). The present study evaluated the signalling events initiated through CD40 ligation which culminate in VSMC chemokine production. CD40 ligation resulted in the phosphorylation/activation of mitogen-activated protein kinases (MAPKs), extracellular signal-regulated kinases 1 and 2 (ERK1/2), and p38, but not c-jun N-terminal kinase. Inhibition of both ERK1/2 and p38 activity abrogated CD40 stimulation of IL-8 and MCP-1 production. CD40-mediated induction of chemokines also showed dependence on the Src family kinase activity. The Src kinase inhibitor, PP2, was found to inhibit CD40-induced phosphorylation of ERK1/2 as well as activation of IkappaB kinase. An evaluation of Src kinases that may be important in CD40 signalling identified Lyn as a potential candidate. These data indicate that CD40 signalling in VSMC activates a Src family kinase-initiated pathway that results in the induction of MAPK activities required for successful induction of chemokine synthesis.     

CD40 signaling of monocyte inflammatory cytokine synthesis through an ERK1/2-dependent pathway. A target of interleukin (il)-4 and il-10 anti-inflammatory action

Ligation of CD40 on monocytes through its interaction with CD40 ligand (CD154) present on activated T helper cells, results in activation of monocyte inflammatory cytokine synthesis and rescue of monocytes from apoptosis induced through serum deprivation. Both of these consequences of CD40 stimulation have been shown to be dependent on the induction of protein tyrosine kinase activity. CD40-mediated activation of protein tyrosine kinase activity and subsequent inflammatory cytokine production are abrogated by treatment of monocytes with the T helper type 2 cytokines interleukin 4 (IL-4) and interleukin 10 (IL-10). In the current study we demonstrate that stimulation of monocytes through CD40 resulted in the phosphorylation and activation of the extracellular signal-regulated kinases 1 and 2 (ERK1/2) mitogen-activated protein kinases, whereas phosphorylation of mitogen-activated protein kinases family members p38 and c-Jun N-terminal kinase was not observed in response to this stimuli over the time course examined. PD98059, an inhibitor of the upstream activator of ERK1/2, the MAP/ERK kinase MEK1/2, suppressed IL-1beta and tumor necrosis factor-alpha production in a dose-dependent fashion. Pretreatment of monocytes with IL-4 and IL-10 inhibited CD40-mediated activation of ERK1/2 kinase activity when used individually, and are enhanced in effectiveness when used in combination. Together, the data demonstrate that CD40-mediated induction of IL-1beta and tumor necrosis factor-alpha synthesis is dependent on a MEK/ERK pathway which is obstructed by signals generated through the action of IL-4 and IL-10.