Hayden L J, Hawk S N, Sih T R, Satre M A
Department of Nutrition, University of California-Davis, One Shields Avenue, Davis, California 95616-8869, USA.
J Cell Physiol. 2001 Mar;186(3):437-47. doi: 10.1002/1097-4652(2000)9999:999<000::AID-JCP1043>3.0.CO;2-5.
The biological effects of vitamin A are mediated in part by retinoic acid (RA) modulation of gene transcription. In this study, we examined whether normal human mammary epithelial cells (HMECs) are biologically responsive to retinol (ROH), the metabolic precursor of RA. While both ROH and tRA resulted in time- and dose-dependent decreases in total cell number, tRA was markedly more potent. Metabolically, treatment of HMECs with physiological doses of ROH resulted in rapid uptake and subsequent production of both retinyl esters and tRA. Although a comparatively minor metabolite, tRA levels peaked at 6 h and remained above endogenous levels for up to 72 h in proportion to cellular ROH concentrations. In HMECs transfected with an RA-responsive luciferase reporter gene, treatment with 3 microM ROH resulted in an increase in luciferase activity to a level intermediate between that observed with 0.001 and 0.01 microM tRA. Citral, an RA-synthesis inhibitor, was also used to examine the biological activity of ROH. Compared to ROH alone, ROH plus citral treatment resulted in three-fold less tRA synthesis and a > 65% attentuation of RA-responsive reporter gene activity which persisted through 72 h. Citral also significantly attenuated the extent of ROH-mediated reductions in total HMEC number. Thus, treatment with physiological concentrations of ROH results in fewer total numbers of HMECs and this response is a consequence of cellular tRA synthesis which can induce RA-responsive gene expression.
维生素A的生物学效应部分是由视黄酸（RA）对基因转录的调节介导的。在本研究中，我们检测了正常人乳腺上皮细胞（HMECs）是否对RA的代谢前体视黄醇（ROH）具有生物学反应。虽然ROH和全反式视黄酸（tRA）均导致细胞总数呈时间和剂量依赖性减少，但tRA的作用明显更强。在代谢方面，用生理剂量的ROH处理HMECs会导致视黄酯和tRA的快速摄取及随后的生成。尽管tRA是一种相对次要的代谢产物，但其水平在6小时达到峰值，并与细胞ROH浓度成比例地在长达72小时内保持高于内源性水平。在用RA反应性荧光素酶报告基因转染的HMECs中，用3 microM的ROH处理导致荧光素酶活性增加至介于用0.001和0.01 microM tRA观察到的水平之间。柠檬醛，一种RA合成抑制剂，也被用于检测ROH的生物学活性。与单独使用ROH相比，ROH加柠檬醛处理导致tRA合成减少三倍，且RA反应性报告基因活性减弱>65%，这种减弱持续72小时。柠檬醛还显著减弱了ROH介导的HMEC总数减少的程度。因此，用生理浓度的ROH处理会导致HMEC总数减少，并且这种反应是细胞tRA合成的结果，而tRA合成可诱导RA反应性基因表达。
