Feliciano David M, Edelman Arthur M
Department of Pharmacology and Toxicology, State University of New York, Buffalo, New York 14214, USA.
J Biol Chem. 2009 Sep 25;284(39):26466-81. doi: 10.1074/jbc.M109.027680. Epub 2009 Jul 24.
Neuroblastoma cells having stem cell-like qualities are widely employed models for the study of neural stem/progenitor cell proliferation and differentiation. We find that human BE(2)C neuroblastoma cells possess a signaling cascade initiated by Ca(2+) influx via voltage-dependent calcium channels and the N-methyl-D-aspartate (NMDA) receptor and culminating in nuclear calmodulin-dependent protein kinase IV (CaMKIV)-mediated phosphorylation and activation of the transcription factors Ca(2+)/cyclic AMP-response element-binding protein (CREB) and ATF1 (activating transcription factor-1). This pathway functions to maintain BE(2)C cells in an undifferentiated, proliferative state. Parallel to this Ca(2+)-dependent pathway is a hormone-responsive program by which retinoic acid (RA) initiates the differentiation of BE(2)C cells toward a neuronal lineage. This is evidenced by RA-dependent induction of the cell cycle inhibitor p21/Cip1 (Cdk-interacting protein 1) and cell cycle arrest, induction of the neuroblastic marker doublecortin and of the neuron-specific intermediate filament protein, peripherin, and by RA-stimulated extension of neuritic processes. During neuronal differentiation there is a complex antagonistic interplay between these two major signaling pathways. RA down-regulates expression of CaMKIV and one of its upstream activators, CaMKK1 (calmodulin-dependent protein kinase kinase 1). This is accompanied by RA-induced suppression of activating phosphorylation of CREB with a time course paralleling that of CaMKIV down-regulation. RA-induced repression of the Ca(2+)/calmodulin-dependent protein kinase kinase/CaMKIV/CREB pathway appears to be involved in regulating the timing of neuronal differentiation, as shown by the effect of RNA interference of CaMKIV to markedly accelerate RA-dependent up-regulation of p21/Cip1 and doublecortin expression and RA-promoted neurite outgrowth. RA-induced repression of the CaMKIV signaling pathway may represent an early event in retinoid-dependent neuronal differentiation.
具有干细胞样特性的神经母细胞瘤细胞是研究神经干细胞/祖细胞增殖和分化的广泛应用的模型。我们发现，人BE(2)C神经母细胞瘤细胞拥有一个信号级联反应，该反应由通过电压依赖性钙通道和N-甲基-D-天冬氨酸（NMDA）受体的Ca(2+)内流启动，并最终导致核钙调蛋白依赖性蛋白激酶IV（CaMKIV）介导的转录因子Ca(2+)/环磷酸腺苷反应元件结合蛋白（CREB）和激活转录因子1（ATF1）的磷酸化和激活。该途径的作用是使BE(2)C细胞维持在未分化的增殖状态。与这条Ca(2+)依赖性途径并行的是一个激素反应程序，通过该程序视黄酸（RA）启动BE(2)C细胞向神经元谱系的分化。这表现为RA依赖性诱导细胞周期抑制剂p21/Cip1（细胞周期蛋白依赖性激酶相互作用蛋白1）和细胞周期停滞，诱导神经母细胞标志物双皮质素和神经元特异性中间丝蛋白外周蛋白，以及RA刺激神经突的延伸。在神经元分化过程中，这两条主要信号通路之间存在复杂的拮抗相互作用。RA下调CaMKIV及其上游激活剂之一钙调蛋白依赖性蛋白激酶激酶1（CaMKK1）的表达。这伴随着RA诱导的CREB激活磷酸化的抑制，其时间进程与CaMKIV下调的时间进程平行。RA诱导的Ca(2+)/钙调蛋白依赖性蛋白激酶激酶/CaMKIV/CREB途径的抑制似乎参与调节神经元分化的时间，如CaMKIV的RNA干扰显著加速RA依赖性p21/Cip1和双皮质素表达上调以及RA促进神经突生长的作用所示。RA诱导的CaMKIV信号通路的抑制可能代表类视黄醇依赖性神经元分化中的一个早期事件。
