Specificity, diversity, and convergence in VEGF and TNF‐α signaling events leading to tissue factor up regulation via EGR‐1 in endothelial cells

Abstract

Tissue factor (TF) has been shown to be up-regulated in endothelial cells by the inflammatory cytokine tumor necrosis factor alpha (TNF-alpha) as well as by the main angiogenic factor VEGF. Since both stimuli induce the transcription factor EGR-1, which is critically involved in TF gene regulation, we used EGR-1-dependent TF induction as a model to identify potential cross-talks between the various signal transduction cascades initiated by VEGF and TNF-alpha. The data show that at the MAP kinase level, VEGF mainly activates ERK1/2 and p38 MAP kinases in human endothelial cells. TNF-alpha is able to activate all three MAP kinase cascades as well as the classical inflammatory IkappaB/NFkappaB pathway. Furthermore, the MEK/ERK module of MAP kinases appears to act as the convergence point of VEGF- and TNF-alpha-initiated signaling cascades, which lead to the activation of EGR-1 and subsequent TF expression, whereas the upstream signals are distinct. We found that induction of TF by VEGF via EGR-1 is strongly PKC dependent. The TNF-alpha-initiated MEK/ERK cascade connected to EGR-1 and TF expression is clearly less sensitive to PKC inhibition. TNF-alpha-mediated activation of MEK/ERK and EGR-1 can be blocked by adenoviral expression of a dominant negative mutant of IKK2, whereas the VEGF signaling pathway is unaffected. Thus, our data demonstrate a new link between the classical inflammatory IKK/IkappaB and the MEK/ERK cascades triggered by TNF-alpha. The additional finding that EGF induces ERK and EGR-1 in a PKC-independent manner and that this signal is not sufficient to up-regulate TF emphasizes the importance of a VEGF-specific signaling pattern for the induction of TF.

Modulation of the oncogene-dependent tissue factor expression by kinase suppressor of ras 1

“…and NFAT) [27][28][29][30]. In cancer cells, the effects of oncogenic EGFR on TF are mediated through an NFκB dependent mechanism [10], as well as by processes involving AP-1 and c-Jun Nterminal kinase (JNK) activation [12].…”

HGF induces fibronectin matrix synthesis in melanoma cells through MAP kinase-dependent signaling pathway and induction of Egr-1

“…Previous studies have established an important role for MEK/MAP kinase in mediating Egr-1 expression in response to other growth factors and hormones (Hodge et al, 1998;Tsai et al, 2000;Mechtcheriakova et al, 2001;Wu et al, 2002). This signaling pathway regulates Egr-1 gene expression mainly through activation of the SREs in the human Egr-1 promoter.…”

NAB2, a Corepressor of EGR-1, Inhibits Vascular Endothelial Growth Factor-mediated Gene Induction and Angiogenic Responses of Endothelial Cells

“…Major signals induced by VEGF via VEGFR-2 in endothelial cells include activation of the phosphoinositol 3-kinase/PKB and phospholipase C-␥/PKC pathways (4,5). Whereas activation of PKB has been primarily implicated in cell survival (6), recent in vitro studies have shown that VEGF treatment of endothelial cells leads to a PKC-dependent activation of the MEK/ERK module of MAP kinases resulting in a rapid up-regulation of the transcription factor EGR-1 (7,8), which has been associated with growth and differentiation of various cell types (9,10). Furthermore, EGR-1 is critically involved in the up-regulation of genes such as tissue factor (TF) (7,8), VEGF receptor-1 (VEGFR-1) (11,12), and urokinase-type plasminogen activator (uPA) (13).…”

“…Whereas activation of PKB has been primarily implicated in cell survival (6), recent in vitro studies have shown that VEGF treatment of endothelial cells leads to a PKC-dependent activation of the MEK/ERK module of MAP kinases resulting in a rapid up-regulation of the transcription factor EGR-1 (7,8), which has been associated with growth and differentiation of various cell types (9,10). Furthermore, EGR-1 is critically involved in the up-regulation of genes such as tissue factor (TF) (7,8), VEGF receptor-1 (VEGFR-1) (11,12), and urokinase-type plasminogen activator (uPA) (13). These genes have been proposed to fulfill important functions for different aspects of vasculogenesis and angiogenesis (1,2,14).…”