Rundhaug J, Gubler M L, Sherman M I, Blaner W S, Bertram J S
Cancer Research Center of Hawaii, University of Hawaii at Manoa, Honolulu 96813.
Cancer Res. 1987 Nov 1;47(21):5637-43.
Previous studies have shown that all-trans-retinoic acid fails to inhibit chemically induced transformation in 10T1/2 cells except at toxic levels, whereas retinol and many synthetic retinoids are potent inhibitors. In contrast, in many systems retinoic acid is a more effective modulator of differentiation and carcinogenesis than is retinol. In any attempt to explain this anomaly, we have studied the differential metabolism of retinoic acid and retinol by 10T1/2 cells and by their initiated and transformed derivatives, and have also reexamined these cells for the presence of retinoid-binding proteins. Whereas retinoic acid was depleted from the medium bathing 10T1/2 and initiated 10T1/2 cells within 48 h of treatment, retinol was concentrated 500-fold by these cells, and disappeared from the culture medium no faster than from cell-free medium. Retinoic acid metabolism by a number of transformed cell lines varied widely. There was no apparent correlation between metabolizing ability and transforming agent (methylcholanthrene, X-rays, fission spectrum neutrons, and plasmid oncogene transfection). Uptake of retinoic acid was seen in all cell lines and was not correlated with its metabolism. Retinol was metabolized minimally by all cell lines tested; metabolism of retinol was not correlated with retinoic acid metabolizing ability. Retinoic acid-induced growth inhibition and cytotoxicity were not correlated with metabolizing ability, suggesting that the rate of metabolism of retinoic acid is not a major determinant of its acute biological effects. Using sensitive radioimmunoassays, cellular retinoic acid- (CRABP) and retino-binding proteins (CRBP) were both detected in 10T1/2 and initiated 10T1/2 cells. CRABP levels of about 16 ng/10(6) cells were about 4-fold higher than CRBP levels. Therefore, lack of CRABP does not explain the failure of retinoic acid to inhibit carcinogen-induced transformation in these cells. These studies suggest that the inability of retinoic acid to inhibit transformation in the 10T1/2 cell system may be due to its rapid metabolism and clearance from the medium. On the other hand, the high cellular uptake and stability of retinol in these cells could be an important factor in the inhibition of neoplastic transformation by this retinoid.
以往的研究表明，全反式维甲酸除非在有毒剂量下，否则无法抑制10T1/2细胞中化学诱导的转化，而视黄醇和许多合成类视黄醇是有效的抑制剂。相比之下，在许多系统中，维甲酸比视黄醇更有效地调节分化和致癌作用。在任何试图解释这种异常现象的尝试中，我们研究了10T1/2细胞及其起始和转化衍生物对视黄酸和视黄醇的差异代谢，并且还重新检查了这些细胞中类视黄醇结合蛋白的存在情况。在处理后48小时内，在培养10T1/2细胞和起始的10T1/2细胞的培养基中，视黄酸被耗尽，而这些细胞将视黄醇浓缩了500倍，并且视黄醇从培养基中消失的速度并不比从无细胞培养基中更快。许多转化细胞系的视黄酸代谢差异很大。代谢能力与转化剂（甲基胆蒽、X射线、裂变谱中子和质粒癌基因转染）之间没有明显的相关性。在所有细胞系中都观察到视黄酸的摄取，并且与其代谢无关。所有测试的细胞系对视黄醇的代谢都极少；视黄醇的代谢与视黄酸代谢能力无关。视黄酸诱导的生长抑制和细胞毒性与代谢能力无关，这表明视黄酸的代谢速率不是其急性生物学效应的主要决定因素。使用灵敏的放射免疫分析法，在10T1/2细胞和起始的10T1/2细胞中均检测到细胞视黄酸结合蛋白（CRABP）和视黄醇结合蛋白（CRBP）。CRABP水平约为16 ng/10⁶细胞，比CRBP水平高约4倍。因此，缺乏CRABP并不能解释视黄酸无法抑制这些细胞中致癌物诱导的转化。这些研究表明，视黄酸无法在10T1/2细胞系统中抑制转化可能是由于其快速代谢并从培养基中清除。另一方面，视黄醇在这些细胞中的高细胞摄取和稳定性可能是这种类视黄醇抑制肿瘤转化的一个重要因素。
