Selective modifications of cellular proteins in intratumoral subpopulations of human colonic carcinoma cells.

Molecular alterations of cellular proteins were assessed in three previously described subpopulations of human colon carcinoma cells that were originally isolated from a single human primary colon carcinoma. The subpopulations designated HCT 116b, HCT 116, and HCT 116a exhibited significant differences in their expression of several biological properties. Immunoautoradiographic analysis of membrane components, fractionated by SDS-PAGE and electrophoretically transferred onto nitrocellulose sheets, distinguished the most aggressive tumor cell subpopulation from the intermediate and least aggressive subpopulations. An elevated expression of antigens of molecular weight in the range of 116-120 kd, 92 kd, 55-66 kd, and 31 kd was found to be associated with the most aggressive subpopulation of HCT 116a cells. The binding pattern of RCA I and WGA lectins to membrane components, fractionated by SDS-PAGE and fixed on nitrocellulose, also distinguished the three subpopulations of cells. Elevated bindings of RCA I to 80-92 kd components of HCT 116b cells and elevated bindings of WGA to 120 kd components of HCT 116a cells distinguished the three subpopulations from one another. Analysis of cellular phosphoprotein profiles, following labeling of the cells with 32Pi in the presence of phosphate-free medium, further distinguished the most aggressive subpopulation from the intermediate and least aggressive subpopulations. High level of phosphorylation of 120 kd and 250 kd nuclear components, 30 and 90 kd cytosolic components, and low level of phosphorylation of lower molecular weight membrane components were found to be associated with the most aggressive subpopulation. It is concluded that differences in the expression of membrane antigens, differences in the glycosylation of membrane components, and the selective phosphorylation and/or dephosphorylation of cellular proteins exist in subpopulations of intratumoral colonic carcinoma cells with different biological properties. These biochemical alterations of cellular proteins may play an important role in the generation of phenotypic diversity and heterogeneity of malignant cells.