Immunocytochemical localization of p21 ras gene product in human hepatoma cell lines and corresponding tumors in athymic mice.

The development of monoclonal antibodies (MAb) against ras protein has made possible to study the expression of ras oncogene by immunohistochemical methods in many human solid tumors. Using the MAb RAP-5 generated against a synthetic peptide having the sequence of amino acids 10-17 of the human T24 ras gene product and the peroxidase anti-peroxidase (PAP) technique, we have observed increased level of ras p21 protein in four human hepatoma cell lines and corresponding tumors in athymic mice. The increased level of p21 is not correlated with the grade of differentiation of tumor cells, nor with the expression of HBsAg. The continuous enhanced expression of ras gene product at the cell line level and after transplantation in athymic mice suggests that the increase in p21 level may be important in the maintenance of the transformed phenotype of the hepatoma cells.