Divisão de Biologia Celular, Coordenação de Pesquisa, Instituto Nacional de Câncer, Rio de Janeiro, Rio de Janeiro, Brasil.
PLoS One. 2011;6(9):e25193. doi: 10.1371/journal.pone.0025193. Epub 2011 Sep 28.
Vascular Endothelial Growth Factor (VEGF) is a major regulator of angiogenesis. VEGF expression is up regulated in response to micro-environmental cues related to poor blood supply such as hypoxia. However, regulation of VEGF expression in cancer cells is not limited to the stress response due to increased volume of the tumor mass. Lipid mediators in particular arachidonic acid-derived prostaglandin (PG)E₂ are regulators of VEGF expression and angiogenesis in colon cancer. In addition, increased osmolarity that is generated during colonic water absorption and feces consolidation seems to activate colon cancer cells and promote PGE₂ generation. Such physiological stimulation may provide signaling for cancer promotion. Here we investigated the effect of exposure to a hypertonic medium, to emulate colonic environment, on VEGF production by colon cancer cells. The role of concomitant PGE₂ generation and MAPK activation was addressed by specific pharmacological inhibition. Human colon cancer cell line Caco-2 exposed to a hypertonic environment responded with marked VEGF and PGE₂ production. VEGF production was inhibited by selective inhibitors of ERK 1/2 and p38 MAPK pathways. To address the regulatory role of PGE₂ on VEGF production, Caco-2 cells were treated with cPLA₂ (ATK) and COX-2 (NS-398) inhibitors, that completely block PGE₂ generation. The Caco-2 cells were also treated with a non selective PGE₂ receptor antagonist. Each treatment significantly increased the hypertonic stress-induced VEGF production. Moreover, addition of PGE₂ or selective EP₂ receptor agonist to activated Caco-2 cells inhibited VEGF production. The autocrine inhibitory role for PGE₂ appears to be selective to hypertonic environment since VEGF production induced by exposure to CoCl₂ was decreased by inhibition of concomitant PGE₂ generation. Our results indicated that hypertonicity stimulates VEGF production in colon cancer cell lines. Also PGE₂ plays an inhibitory role on VEGF production by Caco-2 cells exposed to hyperosmotic stress through EP₂ activation.
血管内皮生长因子（VEGF）是血管生成的主要调节因子。VEGF 的表达会受到与低血氧等不良血液供应相关的微环境信号的上调。然而，癌细胞中 VEGF 的表达调控不仅限于肿瘤体积增加所导致的应激反应。脂类介质，特别是花生四烯酸衍生的前列腺素（PG）E₂，是结肠癌中 VEGF 表达和血管生成的调节剂。此外，在结肠吸收水分和粪便固结过程中产生的渗透压增加似乎会激活结肠癌细胞并促进 PGE₂的产生。这种生理刺激可能为癌症的促进提供信号。在这里，我们研究了暴露于高渗培养基以模拟结肠环境对结肠癌细胞 VEGF 产生的影响。通过特定的药理学抑制来解决伴随的 PGE₂生成和 MAPK 激活的作用。暴露于高渗环境的人结肠癌细胞系 Caco-2 对 VEGF 和 PGE₂的产生有明显的反应。ERK 1/2 和 p38 MAPK 通路的选择性抑制剂抑制 VEGF 的产生。为了研究 PGE₂对 VEGF 产生的调节作用，用 cPLA₂（ATK）和 COX-2（NS-398）抑制剂处理 Caco-2 细胞，这些抑制剂完全阻断了 PGE₂的生成。Caco-2 细胞也用非选择性 PGE₂受体拮抗剂处理。每种处理都显著增加了高渗应激诱导的 VEGF 产生。此外，将 PGE₂或选择性 EP₂受体激动剂添加到激活的 Caco-2 细胞中会抑制 VEGF 的产生。PGE₂ 的自分泌抑制作用似乎是选择性的，因为通过抑制伴随的 PGE₂生成，暴露于 CoCl₂诱导的 VEGF 产生减少。我们的结果表明，高渗刺激结肠癌细胞系中 VEGF 的产生。此外，PGE₂通过 EP₂的激活对暴露于高渗应激的 Caco-2 细胞中 VEGF 的产生起到抑制作用。
