Klinik für Dermatologie, Venerologie und Allergologie, Universitätsklinikum des Saarlandes, 66421 Homburg, Germany.
J Steroid Biochem Mol Biol. 2010 Jul;121(1-2):110-3. doi: 10.1016/j.jsbmb.2010.02.003. Epub 2010 Feb 11.
Malignant melanoma cells express the vitamin D receptor (VDR). However, some melanoma cell lines fail to respond to the antiproliferative effects of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). We reported previously that out of seven melanoma cell lines analyzed, three cell lines (MeWo, SK-Mel28, SM) respond to the antiproliferative effects of 1,25(OH)2D3, while the others (SK-Mel5, SK-Mel25, IGR, Meljuso) are resistant. It was the aim of this study to investigate whether epigenetic mechanisms are of importance for the abrogation of vitamin D signaling in vitamin D resistant melanoma cells. We used the histone deacetylase inhibitor (HDACI) trichostatin A (TSA) and the DNA methyltransferase inhibitor (DNMTI) 5-azacytidine (5-Aza) to elucidate the effects of protein acetylation and of DNA hypermethylation on 1,25(OH)2D3-induced effects on cell proliferation, respectively. Additionally we analyzed the expression of VDR microRNA in 1,25(OH)2D3-responding and resistant melanoma cells. TSA and 5-Aza exerted dose- and time-dependent antiproliferative effects on melanoma cell lines. Interestingly, combination therapy with 1,25(OH)2D3 and TSA exerted synergistic antiproliferative effects in a 1,25(OH)2D3-resistant melanoma cell line (IGR) (p<0.05). Combination therapy with 1,25(OH)2D3 and 5-Aza resulted in synergistic (MeWo after 72 h; p<0.05) or additive (other melanoma cell lines analyzed) antiproliferative effects. Additionally, we could show that VDR mRNA expression is relatively high in two of three 1,25(OH)2D3-responsive melanoma cells as compared to resistant cells, moreover this relatively high VDR expression is associated with low expression of miRNA125b in MeWo and SK-Mel28 cells. Our results suggest that the endogenous VDR mRNA level is inversely associated with expression of miRNA125b in melanoma cell lines analyzed. Moreover, miRNA125b may be involved in the regulation of VDR expression and in the resistance against 1,25(OH)(2)D(3) in melanoma cells. It can be speculated whether miRNA125b may be of prognostic importance and/or may represent a therapeutic target for malignant melanoma. Drugs that influence epigenetic mechanisms might be promising therapeutics for the treatment of metastasized malignant melanoma, alone or in combination with antiproliferative or cytotoxic agents such as 1,25(OH)2D3.
恶性黑色素瘤细胞表达维生素 D 受体（VDR）。然而，一些黑色素瘤细胞系对 1,25-二羟维生素 D3（1,25（OH）2D3）的抗增殖作用无反应。我们之前报道过，在分析的七种黑色素瘤细胞系中，三种细胞系（MeWo、SK-Mel28、SM）对 1,25（OH）2D3 的抗增殖作用有反应，而其他细胞系（SK-Mel5、SK-Mel25、IGR、Meljuso）则有抗性。本研究旨在探讨表观遗传机制是否对维生素 D 抵抗的黑色素瘤细胞中维生素 D 信号的阻断具有重要意义。我们使用组蛋白去乙酰化酶抑制剂（HDACI）曲古抑菌素 A（TSA）和 DNA 甲基转移酶抑制剂（DNMTI）5-氮杂胞苷（5-Aza）来分别阐明蛋白质乙酰化和 DNA 超甲基化对 1,25（OH）2D3 诱导的细胞增殖的影响。此外，我们分析了 1,25（OH）2D3 反应性和抗性黑色素瘤细胞中 VDR microRNA 的表达。TSA 和 5-Aza 对黑色素瘤细胞系表现出剂量和时间依赖性的增殖抑制作用。有趣的是，1,25（OH）2D3 和 TSA 的联合治疗在 1,25（OH）2D3 抗性黑色素瘤细胞系（IGR）中表现出协同的增殖抑制作用（p<0.05）。1,25（OH）2D3 和 5-Aza 的联合治疗导致协同（MeWo 72 小时后；p<0.05）或相加（分析的其他黑色素瘤细胞系）的增殖抑制作用。此外，我们还表明，与抗性细胞相比，三种 1,25（OH）2D3 反应性黑色素瘤细胞中的两种 VDR mRNA 表达相对较高，此外，这种相对较高的 VDR 表达与 MeWo 和 SK-Mel28 细胞中 miRNA125b 的低表达相关。我们的结果表明，内源性 VDR mRNA 水平与分析的黑色素瘤细胞系中 miRNA125b 的表达呈负相关。此外，miRNA125b 可能参与 VDR 表达的调节以及黑色素瘤细胞对 1,25（OH）（2）D（3）的抗性。可以推测 miRNA125b 是否具有预后意义，或者是否可以作为恶性黑色素瘤的治疗靶点。影响表观遗传机制的药物可能是治疗转移性恶性黑色素瘤的有前途的治疗方法，单独或与 1,25（OH）2D3 等增殖或细胞毒性剂联合使用。
