Expression of angiopoietin 1, 2 and their common receptor Tie2 in human gastric carcinoma: implication for angiogenesis

Abstract

Angiogenesis, formation of new microvessels providing oxygen and nutrient supply, is essential for tumor growth. It is dependent on the production of angiogenic growth factors by tumor cells. Angiopoietin 1 (Ang-1) and 2 (Ang-2) and their common receptor, Tie2, are thought to be critical regulators of tumor angiogenesis. We examined expression of Ang-1, Ang-2, and their common receptor Tie2 mRNAs and proteins in gastric cancers using in situ hybridization and immunohistochemistry. We also investigated the relationship between their expression and differentiation of cancer cells, lymph node metastasis, tumor size, depth of cancer cell invasion, TNM staging and microvessel density (MVD). The expression of Ang-1, Ang-2, and Tie2 mRNA in cancer cells significantly correlated with the MVD (p<0.001, <0.001 and =0.019, respectively). Ang-1 and Tie2 positivity correlated with advanced gastric cancers (p<0.05) and larger cancers had higher positive rates of Ang-1, Ang-2, and Tie2 mRNA expression (p<0.001, =0.010 and =0.039, respectively). Significant positive correlations were also found between mRNA expression of Tie2 and those of Ang-1 and Ang-2 (p<0.01 and <0.001, respectively). These findings indicate that the expression of Ang-1 and Ang-2 is important for tumor angiogenesis, and suggest a possible role of autocrine/paracrine function of angiopoietin/Tie2 system in gastric cancer progression.

Fig. 1

(A-E) In situ hybridization for Ang-1, Ang-2 and Tie2 mRNA. (A) Positive Ang-2 expression in well-differentiated cancer cells (arrowheads) with no or only minimal staining on adjacent metaplastic gastric mucosa (arrows) (×100). (B) Moderately differentiated cancer cells show intense cytoplasmic staining for Ang-2 mRNA (×200). (C) Positive Ang-1 mRNA signals on cancer cells (arrowheads, ×100) as well as smooth muscle cells and endothelial cells of large vessels (arrows, Inset, ×400). (D) Poorly differentiated cancer cells (arrowheads) and endothelial cells (arrow) show Tie2 mRNA expression (×100). (E) Infiltrating poorly differentiated carcinoma cells of the muscle layer (arrowheads, ×100) show positive cytoplasmic Tie2 mRNA expression (Inset, ×400). (F-H) Immunohistochemistry for Ang-1, Ang-2 and Tie2 protein. (F) Moderately differentiated cancer cells exhibit Ang-2 protein expression (×200). (G) Immunoreactivity for Ang-1 on smooth muscle cells of vessels (arrows), stromal cells and cancer cells (arrowheads) (×200). (H) Immunohistochemistry for Tie 2. Same cancer area to Fig. E (×100) shows positive cytoplasmic expression on tumor cells (Inset, ×400).