Selective low level of protein kinase C isozyme in a tumor promoter-dependent mouse leukemia cell line

It was found that the activity of protein kinase C in the tumor promoter-dependent cell line (A65T) was significantly lower than that in the independent cell line (A65IND) which was mutated from the dependent cell line. On the other hand, there was no significant difference between these cell lines with regard to cAMP-dependent protein kinase activity. It was found that the maximal binding capacity of 20-3H]phorbol-12,13-dibutyrate of the tumor promoter-dependent cells is lower than that of the independent cells with similar affinities of the two cell lines. Moreover, we found that the level of immunoreactive antigen with monoclonal antibody for type III of protein kinase C in A65T cells was significantly lower than that in the A65IND cells. Thus, this selective lower level of type III of protein kinase C in A65T cells, as compared with A65IND cells means that this difference may be linked to its tumor promoter-dependent cell proliferation.