Abstract
Myofibroblasts, also known as activated fibroblasts, constitute an important niche for tumor development through the promotion of angiogenesis. However, the mechanism of stromal fibroblast activation in tumor tissues has not been fully understood. A gastric cancer mouse model (Gan mice) was recently constructed by simultaneous activation of prostaglandin (PG) E2 and Wnt signaling in the gastric mucosa. Because both the PGE2 and Wnt pathways play a role in human gastric tumorigenesis, the Gan mouse model therefore recapitulates the molecular etiology of human gastric cancer. Microvessel density increased significantly in Gan mouse tumors. Moreover, the expression of vascular endothelial growth factor A (VEGFA) was predominantly induced in the stromal cells of gastric tumors. Immunohistochemistry suggested that VEGFA-expressing cells in the stroma were alpha-smooth muscle actin-positive myofibroblasts. Bone marrow transplantation experiments indicated that a subset of gastric myofibroblasts is derived from bone marrow. Importantly, the alpha-smooth muscle actin index in cultured fibroblasts increased significantly when stimulated with the conditioned medium of Gan mouse tumor cells, indicating that gastric tumor cells activate stromal fibroblasts. Furthermore, conditioned medium of Gan mouse tumor cells induced VEGFA expression both in embryonic and gastric fibroblasts, which further accelerated the tube formation of human umbilical vein endothelial cells in vitro. Notably, stimulation of fibroblasts with PGE2 and/or Wnt1 did not induce VEGFA expression, thus suggesting that factors secondarily induced by PGE2 and Wnt signaling in the tumor cells are responsible for activation of stromal fibroblasts. Such tumor cell-derived factors may therefore be an effective target for chemoprevention against gastric cancer.
Highlights
The promotion of angiogenesis is an important function of myofibroblasts during tumorigenesis
We show that Gan mouse gastric tumor cells activate stromal fibroblasts to become myofibroblasts, and that these myofibroblasts stimulated by gastric tumor cells express vascular endothelial growth factor A (VEGFA) and other angiogenic factors, which may lead to the promotion of angiogenesis
We have previously shown using genetic mouse models that the COX-2/prostaglandin E2 (PGE2) pathway is important for angiogenesis in intestinal polyps [13, 14]
Summary
A gastric cancer mouse model (K19-Wnt1/C2mE mice) was recently established by the transgenic expression of Wnt, cyclooxygenase-2 (COX-2), and microsomal PGE synthase-1 (mPGES-1) in the gastric mucosa [16]. K19-Wnt1/C2mE mice (hereafter Gan mice for Gastric neoplasia) recapitulate a subpopulation of human gastric cancers in molecular mechanism and in tumor pathology. It has been established that PGE2 signaling is important for angiogenesis in intestinal tumors [12,13,14, 22], the mechanisms underlying the induction of angiogenic factors remain to be elucidated. We show that Gan mouse gastric tumor cells activate stromal fibroblasts to become myofibroblasts, and that these myofibroblasts stimulated by gastric tumor cells express VEGFA and other angiogenic factors, which may lead to the promotion of angiogenesis
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