SELECTIVE INCREASES IN ISOFORM PP1-ALPHA OF TYPE-1 PROTEIN PHOSPHATASE IN ASCITES HEPATOMA-CELLS

The amounts of four isoforms of the catalytic subunit of type-1 protei n phosphatases, PP1alpha, PP1gamma1, PP1gamma2, and PP1delta, have bee n determined in extracts of rat ascites hepatomas, AH131A, AH13, AH13N MOR, AH143A, and Yoshida sarcoma, and compared to those of rat liver b y Western blot analysis. The amount of PP1alpha was increased over thr ee times in all five hepatomas. The amount of PP1gamma1 was increased over two times in AH13, AH13NMOR, and AH143A. The amount of PP1delta w as selectively increased about 4 times in AH131A and AH143A. The PP1ga mma2 protein was undetectable in both liver and hepatomas. There was g ood parallelism between the general increase in only PP1alpha protein in the hepatomas and the previous data demonstrating the general incre ase in PP1alpha mRNA in numerous ascites hepatomas. These results sugg est that PP1alpha plays important roles in the expression of malignant phenotype, that its amount is under strict control at the transcripti on level, and that PP1gamma1 and PP1delta play different roles in the expression of some phenotype(s) of the ascites hepatomas.