Sherman M I, Gubler M L, Barkai U, Harper M I, Coppola G, Yuan J
Ciba Found Symp. 1985;113:42-60. doi: 10.1002/9780470720943.ch4.
To study how retinoids promote differentiation and inhibit proliferation of embryonal carcinoma (EC) cells, we have followed their intracellular fate. Retinoic acid (RA) is effectively metabolized to more polar compounds by many EC lines. Unlike RA, retinol is slowly metabolized. Our inability to detect conversion of retinol to RA might indicate that the two retinoids elicit their effects on EC cells in different ways. Retinol added to cultures quickly appears in the nuclear fraction; the proportion associated with nuclei after detergent extraction is initially very low but increases with time. Retinol and RA might be translocated to nuclei by their respective binding proteins [cellular retinol-binding protein (CRBP) and cellular retinoic acid-binding protein (CRABP)]: isolated EC nuclei have specific, independent binding sites for both holoproteins but not their ligands. CRABP cannot be detected in the nucleoplasm of untreated EC cells, but activity is measurable after cells are exposed to RA. Interestingly, incubation with retinol promotes movement of both CRBP and CRABP into the nucleoplasmic fraction. Finally, we have demonstrated that brief exposure to RA dramatically reduces the cloning efficiency of EC cells. Since some cells are unaffected even by lengthy exposures to RA whereas the growth of their progeny is inhibited, we suggest that EC cells can become epigenetically refractory to RA.
为了研究维甲酸如何促进胚胎癌细胞（EC）的分化并抑制其增殖，我们追踪了它们在细胞内的命运。许多EC细胞系可将视黄酸（RA）有效地代谢为极性更强的化合物。与RA不同，视黄醇代谢缓慢。我们无法检测到视黄醇向RA的转化，这可能表明这两种维甲酸以不同方式对EC细胞发挥作用。添加到培养物中的视黄醇很快出现在细胞核部分；去污剂提取后与细胞核相关的比例最初非常低，但随时间增加。视黄醇和RA可能通过它们各自的结合蛋白[细胞视黄醇结合蛋白（CRBP）和细胞视黄酸结合蛋白（CRABP）]转运到细胞核：分离的EC细胞核对两种全蛋白都有特异性、独立的结合位点，但对其配体没有。在未处理的EC细胞核质中检测不到CRABP，但细胞暴露于RA后可检测到其活性。有趣的是，用视黄醇孵育可促进CRBP和CRABP向核质部分移动。最后，我们证明短暂暴露于RA会显著降低EC细胞的克隆效率。由于有些细胞即使长时间暴露于RA也不受影响，而其后代的生长却受到抑制，我们认为EC细胞可能会在表观遗传上对RA产生抗性。
