Increased nm23 protein expression occurs in colorectal adenocarcinoma

The gene nm23 discovered in 1988 by Steeg et al. is a putative tumour and metastasis suppressing gene. Expression of its protein product has been localised in the nucleus and cytoplasm of normal cells. Reduced expression of nm23 is seen in a number of human cancers which have increased incidence of lymph node metastasis and reduced patient survival, a relationship that is strongly demonstrated in a number of human malignancies. However, the role of nm23 in tumours is more complicated than previously thought. This study examines the immunohismchemical expression of the nm23 protein using the Labelled Streptavidin Biotin immunoperoxidase and Immunoelectron Microscopy methods in colorectal carcinomas (n=48) and the corresponding normal mucosa (n=48). The majority of the colorectal carcinomas (32/ 48;67%) were found to express more strongly than the normal corresponding mucosa. In contrast, only a small proportion of carcinoma cases had weaker (4/48;8%) or about equal (12/ 48; 25%) immunoreactivity when compared to the corresponding normal mucosa. The difference in nm23 immunoreactivity between normal and carcinoma tissues was statistically significant (p=0.0001; x ² test with continuity correction). Immunogold KM revealed localisation of the nm23 protein to both the nucleus and cytoplasm of carcinoma and normal cells. Of the 33 colorectal carcinoma cases examined, the majority (n=19; 58%) demonstrated more of the protein deposits in the tumour than in the normal tissue. In contrast, localisation of nm23 protein deposits was less in tumour than in normal tissue in only a small minority (n=5; 15%) of cases. There are up to 9 cases in which approximately equal number of nm23 protein complexes present in both tumour and normal tissue. This study has demonstrated that the nm23 protein expression is increased in colorectal cancers, which is in contrast to the findings of studies of other cancers in which expression of the protein is reduced.