Phorbol ester, retinoic acid and diacylglycerol decrease ecto- but increase total basal-protein kinase activity of human fibroblasts

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Studies have been carried out on intact human lung fibroblasts (HLF) in situ to investigate the effect of the tumor promoter 12-0-tetradecanoylphorbol-13-acetate (TPA) and the anti-tumor promoter retinoic acid (RA) on ecto-protein kinases. The ecto-kinase reaction of the HLF-cells was cAMP-independent, showed an apparent K m for ATP of 6.99 ± 0.35 (μM) and was substantially inhibited by TPA and RA. With the notable exception of a ∼ 57 kD phosphoprotein both compounds decreased the overall phosphorylation of intact cells. In contrast to RA-treatment, however, TPA caused the release of a high molecular weight (∼210 kD) phosphoprotein from the HLF. RA was the most potent retinoid in reducing ecto-kinase activity. The physiological modulators of protein kinase C: 1,2- and 1,3-diolein as well the synthetic 1,2-dioctanoylglycerol decreased the ecto-kinase activity to an extent similar to that of TPA. The drop in ecto-kinase activity of HLF-cells in situ caused by TPA, RA and the diacylglycerols was accompanied by an increase in total basal-(Mg ++-dependent) protein kinase activity present in extracts of treated cells. The results suggest an important role of ecto-kinase in the response of intact cells to TPA and RA.