Mechanisms underlying TGF-β1-induced expression of VEGF and Flk-1 in mouse macrophages and their implications for angiogenesis

Abstract

TGF-beta induces vascular endothelial growth factor (VEGF), a potent angiogenic factor, at the transcriptional and protein levels in mouse macrophages. VEGF secretion in response to TGF-beta1 is enhanced by hypoxia and by overexpression of Smad3/4 and hypoxia-inducible factor-1alpha/beta (HIF-1alpha/beta). To examine the transcriptional regulation of VEGF by TGF-beta1, we constructed mouse reporters driven by the VEGF promoter. Overexpression of HIF-1alpha/beta or Smad3/4 caused a slight increase of VEGF promoter activity in the presence of TGF-beta1, whereas cotransfection of HIF-1alpha/beta and Smad3/4 had a marked effect. Smad2 was without effect on this promoter activity, whereas Smad7 markedly reduced it. Analysis of mutant promoters revealed that the one putative HIF-1 and two Smad-binding elements were critical for TGF-beta1-induced VEGF promoter activity. The relevance of these elements was confirmed by chromatin immunoprecipitation assay. p300, which has histone acetyltransferase activity, augmented transcriptional activity in response to HIF-1alpha/beta and Smad3/4, and E1A, an inhibitor of p300, inhibited it. TGF-beta1 also increased the expression of fetal liver kinase-1 (Flk-1), a major VEGF receptor, and TGF-beta1 and VEGF stimulated pro-matrix metalloproteinase 9 (MMP-9) and active-MMP-9 expression, respectively. The results from the present study indicate that TGF-beta1 can activate mouse macrophages to express angiogenic mediators such as VEGF, MMP-9, and Flk-1.

TGF-β1 Stimulates Mouse Macrophages to Express APRIL through Smad and p38MAPK/CREB Pathways

“…In this context, we have demonstrated that Runx3 synergizes with Smad3/4 to induce Ig germ-line α transcription leading to IgA isotype switching (Park et al, 2003). In addition, HIF-1α cooperates with Smad3/4 to mediate TGFβ1-induced VEGF transcription in mouse macrophages (Jeon et al, 2007). The present data indicate that CREB could play this role in TGFβ1-inducible APRIL transcription.…”

Chemokine Receptor CX3CR1 Mediates Skin Wound Healing by Promoting Macrophage and Fibroblast Accumulation and Function

“…Also, although CX3CL1 directly stimulates angiogenesis, the local microvasculature also depends on several other growth factors, including VEGF and TGF-␤, which are produced by macrophages in wounds (60 -64). TGF-␤ signaling is able to up-regulate VEGF expression in various cell types (65)(66)(67)(68). We also found significant decreases in VEGF gene expression at wound sites in CX3CR1 KO mice.…”

Opposite functions of HIF-α isoforms in VEGF induction by TGF-β1 under non-hypoxic conditions

“…We previously showed that TGF-b1 function is mitogenically conversed in prostate carcinoma cells through the activation of the oncogenic Ras-MAPK signaling pathway (Park et al, 2000). TGF-b1 is involved in blood vessel formation and one of its oncogenic functions is to promote tumor angiogenesis, which is associated with its ability to induce VEGF expression (Benckert et al, 2003;Sugano et al, 2003;Jeon et al, 2007). A recent study demonstrated that TGF-b1 activates migration and invasion of intermediary basal epithelial cells of the prostate by induction of VEGF receptor type 3 and matrix metalloproteinase-2/9, indicating that TGF-b1 is involved in cell phenotype changes associated with transitions to a malignant behavior (Goodyear et al, 2009).…”

“…Expression levels of VEGF and its receptors are increased in prostate cancer cells compared with normal prostate epithelial cells, and elevated VEGF is implicated in angiogenic and non-angiogenic events, which are associated with tumor progression, including early tumor spread (Jackson et al, 2002;Pallares et al, 2006). TGF-b1 has an important role in angiogenesis, and one of the tumor-promoting functions of TGF-b1 is associated with its ability to induce VEGF (Benckert et al, 2003;Sugano et al, 2003;Wang et al, 2004;Jeon et al, 2007). Recently, it was reported that TGF-b1 activates cell migration and invasion by coordinated induction of VEGF receptor type 3 and matrix metalloproteinase-2/9 in intermediary basal epithelial cells of the prostate, suggesting that TGF-b1 is involved in phenotype changes associated with transitions to a malignant behavior (Goodyear et al, 2009).…”