Characterization of cytosolic calcium-activated phospholipid-dependent protein kinase activity in embryonal carcinoma cells. Effect of retinoc acid-induced differentiation of F9 cells to parietal endoderm

Abstract

We have addressed the question of the possible presence of calcium-activated phospholipid-dependent protein kinase (Ca2+-PL protein kinase) activity in undifferentiated embryonal carcinoma cells, and if this activity might be altered during differentiation to a parietal endoderm cell type. Undifferentiated nullipotent F9 embryonal carcinoma cells, as well as differentiated parietal endoderm cells (PYS-2), were utilized. Using an in vitro assay with histone H1 as phosphate acceptor, Ca2+-PL protein kinase activity could not be found in the 100,000 X g supernatant prepared from either cell type. However, passage of 100,000 X g supernatant from PYS cells over a DEAE-cellulose column revealed Ca2+-PL protein kinase activity which eluted with 0.045 M NaCl. The partially purified PYS enzyme has an approximate Mr = 70,000 as determined by Sephadex G-150 gel filtration, and exhibits an apparent Ka for Ca2+ of 32 microM. The PYS Ca2+-PL protein kinase also exhibits a requirement for Mg2+, with maximal activity noted at 10 mM Mg2+. This enzyme is stimulated by acidic phospholipids, while neutral phospholipids such as phosphatidylcholine have little effect. Diacylglycerol markedly increased histone H1 phosphorylation in the presence of Ca2+ and phospholipid. Unlike that of PYS cells, when the 100,000 X g supernatant prepared from F9 cells was passed over a DEAE-cellulose column no Ca2+-PL protein kinase activity could be found in the eluted fractions. Previously it has been reported that exposure of F9 cells to all-trans-retinoic acid induces differentiation to a parietal endoderm cell type. Treatment of F9 cells with 0.1 microM retinoic acid provoked a time-dependent increase in cytosolic Ca2+-PL protein kinase activity as measured after DEAE-cellulose chromatography of the 100,000 X g supernatant. This increase in Ca2+-PL protein kinase activity correlates with differentiation to the parietal endoderm cell type. These findings indicate that cytosolic Ca2+-PL protein kinase activity is very low, or nonexistent, in undifferentiated embryonal carcinoma stem cells. With differentiation to a parietal endoderm cell type there is a marked increase in soluble Ca2+-PL protein kinase activity which exhibits properties similar to those described for this enzyme in other differentiated tissues.