PGE2 receptors and synthesis in human gastric mucosa: perturbation in cancer

Abstract

Recent evidence suggests that prostanoids are an important participant in the pathobiology of gastric adenocarcinoma, but the location and identity of cells in tumor-adjacent gastric mucosa able to synthesize and/or bind specific prostanoids is not clear. Using probes for cyclooxygenase 1 and 2 mRNA and protein as well as for the EP family of PGE2 receptors, we sought to define the biology of prostanoids in adjacent human gastric mucosa at the site of tumor invasion.In mucosa adjacent to an invasive gastric adenocarcinoma, expression of cyclooxygenase was prominent, with COX 1 primarily in mucosal T lymphocytes surrounding nests of tumor cells. Densitometry showed these tumor-adjacent cells had substantial levels of COX 1 immunoreactive protein (relative intensity, 3.2). Cyclooxygenase 2 was newly expressed among these cells as well, but was limited in number (<25% of cyclooxygenase-positive T lymphocytes) in tumor-adjacent mucosa. Further, CD3+ mononuclear cells, adjacent to tumor, strongly expressed prostanoid receptor EP4 (relative intensity, 8.0), but cells with this receptor were not evident in the tumor itself. In contrast, normal gastric mucosa showed a consistent and structured expression of cyclooxygenase and PGE2 receptor immunoreactive protein among mucosal cells. Cyclooxygenase 1 and PGE2 receptor EP4 were expressed on mucosal CD3+ T lymphocytes in the lumenal (upper) third of gastric mucosa; and prostanoid receptors EP2, EP3 and EP4, on gastric epithelia lining gastric pits. In situ hybridization with COX cDNAs confirmed these findings, and neither COX 2-specific mRNA nor protein was detected in normal gastric tissue. Our studies suggest that synthetic machinery and receptors for PGE2, prominently expressed by T lymphocytes in gastric mucosa at the boundary of normal mucosa with tumor cells, may play a central role in prostanoid-driven tumorigenesis of this tissue.