MOLECULAR CHARACTERIZATION OF CELLULAR PROTEINS FROM COLORECTAL TUMORS

Aims and background: Recent evidence has suggested that progressive st ages of colorectal tumorigenesis can be defined by a sequence of genet ic events characterized by altered expression of certain genes and the appearance of cancer-specific proteins. Although the significance of these events is still not clear, expression of cancer-specific protein components may be directly involved in the neoplastic transformation. The purpose of the present study was to compare molecular characteris tics of cellular proteins from human colorectal tumors and normal colo nic mucosa. Methods: Normal mucosa and colorectal tumors from 18 patie nts were fractionated by a differential centrifugation scheme into fou r cellular fractions, i.e., nuclear, mitochondrial (10P) microsomal (1 00P) and cytosolic (100S). The proteins of these fractions from normal and tumorigenic mucosa were analyzed by one-dimensional polyacrylamid e gel electrophoresis followed by Coomassie brilliant blue R-250 and s ilver nitrate staining. Nuclear proteins from normal and neoplastic ti ssues which had revealed the most significant diversities were further characterized by two-dimensional gel electrophoresis. Electrophoretic ally cancer-specific nuclear proteins in the molecular mass zone 35-40 kDa were used as immunogen to produce rabbit polyclonal antibodies. R esults: Electrophoretic analysis by one-dimensional gel electrophoresi s showed clear differences in molecular characteristics of cellular pr oteins between normal and tumorigenic mucosa, especially among nuclear fractions. The latter were also confirmed by their two-dimensional el ectrophoresis results. Rabbit antibodies raised against electrophoreti cally specific nuclear proteins characterized by molecular mass of 35- 40 kDa cross-reacted with 36 kDa polypeptide in 15 of 18 (83.3%) studi ed nuclear fractions of colorectal tumors but not with any normal muco se. In same cases, nuclear cancer-associated components of 38 and 40 k Da were also recognized by these antibodies. Conclusions: During color ectal carcinogenesis, specific expression of several nuclear proteins takes place. One of them, the polypeptide of 38 kDa not found in norma l colonic epithelium, was shared by over 83% of the studied carcinomas despite variations in detailed cancer properties. This particular nuc lear protein may be considered as a potential marker for the colon mal ignancy.