Dept. of Pathology and Laboratory Medicine, Center for Cancer Research, Univ. of Tennessee Health Science Center, 930 Madison Ave., RM525, Memphis, TN 38163, USA.
Am J Physiol Cell Physiol. 2011 Mar;300(3):C526-41. doi: 10.1152/ajpcell.00203.2010. Epub 2010 Dec 15.
20-hydroxyvitamin D(2) [20(OH)D(2)] inhibits DNA synthesis in epidermal keratinocytes, melanocytes, and melanoma cells in a dose- and time-dependent manner. This inhibition is dependent on cell type, with keratinocytes and melanoma cells being more sensitive than normal melanocytes. The antiproliferative activity of 20(OH)D(2) is similar to that of 1,25(OH)(2)D(3) and of newly synthesized 1,20(OH)(2)D(2) but significantly higher than that of 25(OH)D(3). 20(OH)D(2) also displays tumorostatic effects. In keratinocytes 20(OH)D(2) inhibits expression of cyclins and stimulates involucrin expression. It also stimulates CYP24 expression, however, to a significantly lower degree than that by 1,25(OH)(2)D(3) or 25(OH)D(3). 20(OH)D(2) is a poor substrate for CYP27B1 with overall catalytic efficiency being 24- and 41-fold lower than for 25(OH)D(3) with the mouse and human enzymes, respectively. No conversion of 20(OH)D(2) to 1,20(OH)(2)D(2) was detected in intact HaCaT keratinocytes. 20(OH)D(2) also demonstrates anti-leukemic activity but with lower potency than 1,25(OH)(2)D(3). The phenotypic effects of 20(OH)D(2) are mediated through interaction with the vitamin D receptor (VDR) as documented by attenuation of cell proliferation after silencing of VDR, by enhancement of the inhibitory effect through stable overexpression of VDR and by the demonstration that 20(OH)D(2) induces time-dependent translocation of VDR from the cytoplasm to the nucleus at a comparable rate to that for 1,25(OH)(2)D(3). In vivo tests show that while 1,25(OH)(2)D(3) at doses as low as 0.8 μg/kg induces calcium deposits in the kidney and heart, 20(OH)D(2) is devoid of such activity even at doses as high as 4 μg/kg. Silencing of CY27B1 in human keratinocytes showed that 20(OH)D(2) does not require its transformation to 1,20(OH)(2)D(2) for its biological activity. Thus 20(OH)D(2) shows cell-type dependent antiproliferative and prodifferentiation activities through activation of VDR, while having no detectable toxic calcemic activity, and is a poor substrate for CYP27B1.
20-羟维生素 D（2）[20（OH）D（2）]以剂量和时间依赖的方式抑制表皮角质形成细胞、黑素细胞和成黑素瘤细胞的 DNA 合成。这种抑制作用依赖于细胞类型，角质形成细胞和成黑素瘤细胞比正常黑素细胞更为敏感。20（OH）D（2）的抗增殖活性与 1,25（OH）（2）D（3）和新合成的 1,20（OH）（2）D（2）相似，但明显高于 25（OH）D（3）。20（OH）D（2）还具有肿瘤抑制作用。在角质形成细胞中，20（OH）D（2）抑制细胞周期蛋白的表达，并刺激 involucrin 的表达。它还刺激 CYP24 的表达，但程度明显低于 1,25（OH）（2）D（3）或 25（OH）D（3）。20（OH）D（2）是 CYP27B1 的不良底物，其整体催化效率分别比小鼠和人酶中的 25（OH）D（3）低 24 倍和 41 倍。在完整的 HaCaT 角质形成细胞中未检测到 20（OH）D（2）转化为 1,20（OH）（2）D（2）。20（OH）D（2）还具有抗白血病活性，但效力低于 1,25（OH）（2）D（3）。20（OH）D（2）的表型效应是通过与维生素 D 受体（VDR）相互作用介导的，这可通过沉默 VDR 后细胞增殖的衰减、通过稳定过表达 VDR 增强抑制作用以及通过证明 20（OH）D（2）以与 1,25（OH）（2）D（3）相当的速度诱导 VDR 从细胞质向细胞核的时间依赖性易位来证明。体内试验表明，虽然 1,25（OH）（2）D（3）的剂量低至 0.8μg/kg 就会在肾脏和心脏中引起钙沉积，但 20（OH）D（2）即使在高达 4μg/kg 的剂量下也没有这种活性。在人角质形成细胞中沉默 CY27B1 表明，20（OH）D（2）不需要转化为 1,20（OH）（2）D（2）即可发挥其生物学活性。因此，20（OH）D（2）通过激活 VDR 表现出细胞类型依赖性的抗增殖和促分化活性，而没有可检测到的毒性钙活性，并且是 CYP27B1 的不良底物。
