Differential expression of peroxisome proliferator-activated receptor in histologically different human gastric cancer tissues.

Gastric cancer cell lines express peroxisome proliferator-activated receptor gamma (PPARgamma), and treatment with PPARgamma ligands suppresses growth of subgroup of these cell lines. However, expression and subcellular distribution of PPARgamma in human gastric cancer tissues is still unknown. Therefore, expression and subcellular localization of PPARgamma were examined among different histological types of gastric cancer tissues. Immunohistochemical staining for PPARgamma was performed using biopsy specimens of human gastric cancer of various histological types, gastric adenomas, and intestinal metaplasia. All samples of intestinal metaplasia and most samples of gastric tumors, except for signet ring cell carcinoma, expressed PPARgamma in the epithelial cells. Most samples of signet ring cell cancer lacked PPARgamma expression. All samples of intestinal metaplasia expressed PPARgamma only in the cytosol. For adenoma, 90% was positive for PPARgamma in cytosol, and 40% was positive in nuclei, for well-differentiated adenocarcinoma, 80% was positive in cytosol, and 20% was positive in nuclei. For moderately differentiated adenocarcinomas, 70% was positive for cytosol, and 80% was positive for nuclei; for poorly differentiated adenocarcinoma, 30% was positive in cytosol, and 70% was positive in nuclei. The frequency of samples with positive cytosolic staining decreased as the differentiation stage turned from intestinal metaplasia to adenoma, well-, moderately-, and poorly-differentiated cancers. Simultaneously, there was a tendency toward an increased frequency of samples with positive nuclear PPARgamma staining as the differentiation stage transformed from intestinal metaplasia to poorly-differentiated cancer. There was a striking difference in subcellular localization according to the differentiation levels of gastric dysplastic cells. The findings also supported an intestinal metaplasia-adenoma-well-differentiated gastric cancer sequence, and signet ring cell cancer was suggested to be of a different lineage from other types of gastric cancers.