Background: The inducible nitric (NO) synthase 2 (NOS2) is upregulated in breast, brain, colon, and gynecological tumors, which indicate that NO may have a role in tumorigenesis. However, little is known about the role and regulation of NOS2 in colorectal carcinomas. Recent in vitro experiments have implicated that NOS2 is downregulated by p53 accumulation. Virtual analysis of the NOS2 promoter showed putative TCF-4/Lef-1 response elements, which indicate a potential regulation of NOS2 expression by activation of the adenomatous polyposis coli (APC)/beta-catenin pathway.
Methods: NOS2 mRNA expression was investigated in 59 colorectal carcinomas by reverse transcriptase/real-time polymerase chain reaction and related to mutations in the p53, APC, and beta-catenin genes. Presence of NOS2 protein was studied by Western blot, and the localization was studied by immunohistochemistry. Loss of heterozygosity was studied in the region of the NOS2 gene.
Results: The NOS2 mRNA and protein expression were significantly higher in tumors than in control tissue. Immunohistochemistry revealed extensive NOS2 staining in the epithelial cells and, to a minor degree, in leukocytes. Increased NOS2 mRNA expression was found in Dukes' stages A and B compared with the C and D stages. No relationship was found between elevated NOS2 expression and loss of heterozygosity in the later stages according to Dukes' classification or mutations in the p53, APC, or beta-catenin genes.
Conclusions: Inactivating mutations in the p53 and APC pathways are not the main explanation for the increased NOS2 expression found in colorectal tumors.