Chromosomal proteins in hepatocarcinogenesis.

The chromosomal proteins of rat liver were studied by SDS-gel electrophoresis during the process of nitrosomorpholine-induced hepatocarcinogenesis, in the primary hepatomas thus obtained, and in their metastases. It was found that an increased proteolytic activity was present in liver homogenates from carcinogen-fed animals which caused differences between the nonhistone chromosomal proteins of control and carcinogen-treated livers. These differences disappeared in the presence of the protease inhibitor PMSF. In the primary hepatomas slight quantative changes were observed: an increased amount of two proteins of 43000 and 63000 daltons molecular weight, respectively, and a decrease in the histone subfraction H 1 degrees. In the metastases both quantative and qualitative differences were detected: a strong decrease in the protein bands corresponding to the contractile proteins alpha-tubulin, beta-tubulin, and actin; an increased content of the 63000 dalton protein; the appearance of new proteins of approximately 60000, 90000, and 120000 daltons molecular weight, and the complete disappearance of histone H 1 degrees.