Effect of narrow fractions of chromatin non-histone proteins on the expression of membrane tumor-associated antigen MA-50 and phosphorylation of proteins of cultured rat hepatocytes

As earlier reported, the main component of narrow fractions of chromosomal non-histone proteins (NHP) of kidney and of Zaidel hepatoma cells has its own protein kinase activity, and is identified as a heteroorgan NHP-antigen, which is intrinsic to the definite renal tissue and absent in the liver. Effects of narrow fractions of kidney and Zaidel hepatoma NHP on biosynthetic processes and sizes of hepatocytes were studied in vitro. It has been shown that as a result of a 5 h incubation of rat hepatocytes with a narrow fraction of renal NHP the proportion of small hepatocytes increases approximately by 12% as compared with that of cells cultivated without NHP. Besides, binding of organ-specific anti-kidney immune serum with a small hepatocyte population rises by more than 20%, which results from the expression of tumor-associated heteroorgan kidney-specific antigen on the hepatocyte surface. According to immunoprecipitation and subsequent electrophoresis, the molecular mass of a membrane heteroorgan antigen on the surface of hepatocytes amounts approximately to 65 kDa, and an active phosphorylation of cellular proteins takes place. The same effect on hepatocytes is produced by a narrow NHP fraction of chromatin of Zaidel hepatoma cells, whereas no phosphorylation is observed in the presence of liver NHP as well as in the absence of NHP. It is suggested that the heteroorgan NHP-antigen induces biosynthetic processes including synthesis of membrane tumorassociated antigen on the surface of hepatocytes cultivated in vitro by activation of cellular protein phosphorylation, which can lead to changes in size of cultivated cells.