Vitamin D3 and its metabolites have antitumorigenic properties in vitro and in vivo; however, clinical trials and retrospective studies on the effectiveness of vitamin D3 oral supplementation against cancer have been inconclusive. One reason for this may be that clinical trials ignore the complex vitamin D metabolome and the many active vitamin D3 metabolites present in the body. Recent work by our lab showed that 24R,25(OH)2D3, a vitamin D3 metabolite that is active in chondrocyte proliferation and differentiation, has antitumorigenic properties in estrogen receptor alpha-66 (ERα66)–positive (ER+) breast cancer, but not in ERα66-negative (ER−) breast cancer. Here we show that 24R,25(OH)2D3 is protumorigenic in an in vivo mouse model (NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (NSG) mice) of ER− breast cancer, causing greater tumor growth than in mice treated with vehicle alone. In vitro results indicate that the effect of 24R,25(OH)2D3 is via a membrane-associated mechanism involving ERs and phospholipase D. 24R,25(OH)2D3 increased proliferation and reduced apoptosis in ERα66-negative HCC38 breast cancer cells, and stimulated expression of metastatic markers. Overexpressing ESRI, which encodes ERα66, ERα46, and ERα36, reduced the proapoptotic response of ERα66− cells to 24R,25(OH)2D3, possibly by upregulating ERα66. Silencing ESR1 in ERα66+ cells increased apoptosis. This suggests 24R,25(OH)2D3 is differentially tumorigenic in cancers with different ERα isoform profiles. Antiapoptotic actions of 24R,25(OH)2D3 require ERα36 and proapoptotic actions require ERα66. Implications: These results suggest that 24R,25(OH)2D3, which is a major circulating metabolite of vitamin D, is functionally active in breast cancer and that the regulatory properties of 24R,25(OH)2D3 are dependent upon the relative expression of ERα66 and ERα36.

中文翻译：

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ERα同工型ERα66和ERα36的相对表达控制乳腺癌细胞对24R,25-二羟基维生素D3的反应

维生素 D3 及其代谢物在体外和体内均具有抗肿瘤特性；然而，关于维生素 D3 口服补充剂抗癌效果的临床试验和回顾性研究尚无定论。造成这种情况的一个原因可能是临床试验忽略了复杂的维生素 D 代谢组和体内存在的许多活性维生素 D3 代谢物。我们实验室最近的工作表明，24R,25(OH)2D3 是一种维生素 D3 代谢物，在软骨细胞增殖和分化中具有活性，在雌激素受体 α-66 (ERα66) 阳性 (ER+) 乳腺癌中具有抗肿瘤特性，但在在 ERα66 阴性 (ER-) 乳腺癌中。在这里，我们显示 24R,25(OH)2D3 在 ER- 乳腺癌的体内小鼠模型（NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (NSG) 小鼠）中具有致瘤性，导致比仅用载体处理的小鼠更大的肿瘤生长。体外结果表明，24R,25(OH)2D3 的作用是通过涉及 ER 和磷脂酶 D 的膜相关机制。24R,25(OH)2D3 在 ERα66 阴性 HCC38 乳腺癌细胞中增加增殖并减少细胞凋亡，并且刺激转移标志物的表达。过度表达编码 ERα66、ERα46 和 ERα36 的 ESRI 可能通过上调 ERα66 降低 ERα66-细胞对 24R、25(OH)2D3 的促凋亡反应。沉默 ERα66+ 细胞中的 ESR1 会增加细胞凋亡。这表明 24R,25(OH)2D3 在具有不同 ERα 异构体谱的癌症中具有不同的致瘤性。24R,25(OH)2D3 的抗凋亡作用需要 ERα36，促凋亡作用需要 ERα66。启示：这些结果表明 24R、25(OH)2D3、