Expression of autophosphorylating protein kinase 500 in normal and neoplastic rat cells.

Autophosphorylating protein kinase 500 (AUT-PK 500) is a unique serine protein kinase that was originally purified and characterized from the rat adrenocortical carcinoma. A specific RIA with an assay sensitivity of 10 ng (0.02 pmol) was developed for AUT-PK 500 and applied to normal, embryonic, fetal, neonatal, immortal, and neoplastic tissues and cultured cells. As compared to normal rat tissues, the expression of AUT-PK 500 is elevated 100-fold in spontaneously occurring adrenocortical carcinoma 494, 50- to 60-fold in four chemically induced, rapidly growing hepatomas, 30-fold in the chemically induced mammary carcinoma, 20-fold in the cultured hepatoma cell line, and 4-fold in the Rat I and Rat II established tissue culture cell lines. There was also a 5-fold increase in the enzyme when freshly cultured rat skin epithelial-like cells were established. Furthermore, in vivo studies showed that when the rat liver was chemically transformed into its premalignant altered foci, there was a 7-fold elevation of AUT-PK 500. Embryonic cells and fetal and neonatal tissues contained barely detectable (less than 0.22 micrograms/mg of protein) amounts of the protein kinase. These results suggest that AUT-PK 500 is not involved in the differentiation process during fetal development but may be elevated during early steps of carcinogenesis and is further elevated during later stages.