Ways D K, Dodd R C, Bennett T E, Hooker J L, Earp H S
Department of Medicine, East Carolina University, Greenville, North Carolina 27834-4354.
Cancer Res. 1988 Oct 15;48(20):5779-87.
Phorbol esters stimulate differentiation of certain human leukemic cell lines. Although activation of protein kinase C may mediate certain effects of phorbol esters, controversy exists as to the role of protein kinase C activation in phorbol ester-induced differentiation. Retinoic acid modulates responses to phorbol esters in several cell types. Retinoic acid has also been found to alter protein kinase C-dependent phosphorylation in leukemic cells. We correlated the effects of retinoic acid on protein kinase C-dependent phosphorylation and differentiation stimulated by 12-O-tetradecanoylphorbol-13-acetate (TPA), a phorbol ester, in the human monoblastoid U937 cell line. At concentrations less than 1 nM, which were 100-fold less than those directly stimulating differentiation, retinoic acid potentiated TPA-induced differentiation of the U937 cell as assessed by enhanced adherence to plastic and acquisition of nonspecific esterase activity. TPA-stimulated decreases in cellular proliferation were not affected by retinoic acid treatment. Without altering the sensitivity to TPA, retinoic acid increased the maximal response to this agent. Retinoic acid enhanced TPA-stimulated phosphorylation of a Mr 48,000 substrate in intact 32P-labeled U937 cells and also increased the protein kinase C-dependent phosphorylation of a similar Mr 48,000 substrate and a Mr 80,000 substrate in cellular extracts. In cellular extracts the retinoic acid-induced enhancement of protein kinase C-dependent phosphorylation was predominantly localized to the cytosolic fraction. Increases in protein kinase C-dependent phosphorylation were evident within a 12-h exposure to 1 nM retinoic acid and were observed at retinoic concentrations of 0.01 to 1 nM. A retinoic acid-induced increase in the protein kinase C-dependent phosphorylation of an exogenous substrate, histone, was observed following diethylaminoethyl extraction of cytosol, but not a solubilized particulate fraction. The conditions of retinoic acid treatment increasing protein kinase C activity and enhancing protein kinase C-dependent phosphorylation of endogenous substrates were similar to those conditions potentiating phorbol ester-induced differentiation. Thus, the retinoic acid-induced amplification of phorbol ester signal transduction at the level of protein kinase C activation could mediate the effects of this vitamin on phorbol ester-induced differentiation.
佛波酯可刺激某些人白血病细胞系的分化。尽管蛋白激酶C的激活可能介导佛波酯的某些效应，但关于蛋白激酶C激活在佛波酯诱导分化中的作用仍存在争议。维甲酸可调节几种细胞类型对佛波酯的反应。还发现维甲酸可改变白血病细胞中蛋白激酶C依赖性磷酸化。我们将维甲酸对蛋白激酶C依赖性磷酸化的影响与12 - O - 十四烷酰佛波醇 - 13 - 乙酸酯（TPA，一种佛波酯）在人单核细胞样U937细胞系中刺激的分化相关联。在浓度低于1 nM时，该浓度比直接刺激分化的浓度低100倍，通过增强对塑料的黏附性和获得非特异性酯酶活性评估，维甲酸增强了TPA诱导的U937细胞分化。TPA刺激的细胞增殖减少不受维甲酸处理的影响。在不改变对TPA敏感性的情况下，维甲酸增加了对该试剂的最大反应。维甲酸增强了完整的32P标记的U937细胞中Mr 48,000底物的TPA刺激的磷酸化，并且还增加了细胞提取物中类似的Mr 48,000底物和Mr 80,000底物的蛋白激酶C依赖性磷酸化。在细胞提取物中，维甲酸诱导的蛋白激酶C依赖性磷酸化增强主要定位于胞质部分。在暴露于1 nM维甲酸12小时内，蛋白激酶C依赖性磷酸化增加，并且在0.01至1 nM的维甲酸浓度下观察到。在对胞质溶胶进行二乙氨基乙基提取后，观察到维甲酸诱导的外源性底物组蛋白的蛋白激酶C依赖性磷酸化增加，但在可溶的颗粒部分未观察到。增加蛋白激酶C活性并增强内源性底物的蛋白激酶C依赖性磷酸化的维甲酸处理条件与增强佛波酯诱导分化的条件相似。因此，维甲酸在蛋白激酶C激活水平上诱导的佛波酯信号转导放大可能介导了这种维生素对佛波酯诱导分化的作用。
