Acidic Extracellular pH Induces Vascular Endothelial Growth Factor (VEGF) in Human Glioblastoma Cells via ERK1/2 MAPK Signaling Pathway

Abstract

Overexpression of vascular endothelial growth factor (VEGF) is associated with disease progression in human glioblastomas. We recently showed that VEGF promoter activity is inversely correlated with tumor extracellular pH (pH o ) in vivo in the human glioma (U87 MG) xenografts. Here we show that substitution of the neutral culture medium (pH 7.3) with acidic pH medium (pH 6.6) up-regulates VEGF mRNA and protein production in human glioblastoma cells as reflected by Northern blot analysis and enzyme-linked immunosorbent assay. Functional analysis of the VEGF promoter reveals that the sequence between ؊961 bp and ؊683 bp upstream of the transcription start site is responsible for the transcriptional activation of the VEGF gene by acidic pH. This region contains the binding site for AP-1. Consequently, AP-1 luciferase reporter gene was activated by acidic pH. Gel-shift analysis confirmed that AP-1 DNA binding activity is induced under acidic pH. While investigating the upstream signaling pathways, we found that ERK1/2 MAPK is activated and translocates to the nucleus to activate Elk-1, and inhibition of the activation of ERK by specific inhibitors of MEK1 blocks the up-regulation of VEGF by low pH. Dominant negative forms of Ras and Raf abolished the activation of VEGF promoter by acidic pH. These results show that acidic pH activates Ras and the ERK1/2 MAPK pathway to enhance VEGF transcription via AP-1, leading to increased VEGF production.

Acidosis Improves Uptake of Antigens and MHC Class I-Restricted Presentation by Dendritic Cells

“…In this regard, however, it should be mentioned that low extracellular pH is able to activate mitogen-activated protein kinases extracellular signal-regulated kinase 2, c-Jun N-terminal kinase, and p38 in a variety of cell types (64,65). More interestingly, changing extracellular pH from 7.4 to 6.1 has shown to trigger the activation of PLC with the subsequent production of inositol trisphosphates and Ca 2ϩ mobilization, in human fibroblasts, endothelial, smooth muscle, and neuroblastoma cells, but not in human epidermoid carcinoma (A431) cells (66).…”

Extracellular Acidosis Induces Neutrophil Activation by a Mechanism Dependent on Activation of Phosphatidylinositol 3-Kinase/Akt and ERK Pathways

“…Previous studies have shown that low extracellular pH is able to activate ERK2, JNK, and p38 MAPK in a variety of cell lines (55,56). Moreover, decreasing extracellular pH from 7.4 to 6.1 has shown to be capable to activate phospholipase C, leading to Ca 2ϩ mobilization and the production of inositol triphosphates in human fibroblast, endothelial, smooth muscle, and neuroblastoma cells (57).…”

Sequential changes in vessel formation and micro-vascular function during bone repair

“…Microcirculatory properties govern not only the efficacy of substrate delivery but also the metabolic microenvironment, which is in turn essential for regulation of gene expression (Shweiki et al 1992, Mukhopadhyay et al 1995, Mazure et al 1996, Xu et al 2002. The dynamics of alteration of the microcirculation after destruction of bone integrity are essential for angiogenesis and osteogenesis (Rhinelander 1968, Glowacki 1998, Gerber et al 1999.…”