1,25双羟维生素D及其受体对分化型甲状腺癌细胞增殖与分化的调节机制

Thyroid cancer has the fastest rising incidence among cancers, especially differentiated thyroid carcinoma (DTC) which includes papillary thyroid carcinoma and follicular thyroid carcinoma. Their prognosis is largely depending on the degree of the cancer cell differentiation. However, the factors which determine DTC differentiation are unclear, which makes research on DTC prevention and treatment difficult. We have found that the levels of vitamin D receptor (VDR) positively correlate with the degree of DTC differentiation in human thyroid cancer specimens and 1,25-dihydroxyvitamin D and VDR regulate differentiation and proliferation of DTC cells. However, the mechanism by which 1,25-dihydroxyvitamin D regulates differentiation and proliferation is unclear. We hypothesize that 1,25-dihydroxyvitamin D inhibits proliferation of DTC cells via CCAAT/enhancer binding protein β (C/EBPβ) and VDR inhibits proliferation of DTC and promotes differentiation of DTC via E-cadherin. To test this hypothesis, we will reduce the expression of C/EBPβ or E-cadherin in papillary thyroid carcinoma and follicular thyroid carcinoma and determine whether 1,25-dihydroxyvitamin D and VDR alter DTC cell proliferation, differentiation, and tumor growth. Successful completion of the project will determine the mechanism by which 1,25-dihydroxyvitamin D and its receptor regulate differentiation and proliferation of DTC and will help uncover novel clues for preventive and therapeutic strategies of the disease.

甲状腺癌为发病率增长最快的肿瘤，其中以分化型甲状腺癌（DTC）常见，包括乳头状和滤泡状甲状腺癌，两者预后与它们的分化程度密切相关，但由于决定DTC分化的因素并不清楚，使DTC的防治研究成为一大难题。我们发现，在人的DTC组织中，细胞内维生素D受体（VDR）表达水平与癌组织的分化程度呈正相关，并且1,25-双羟维生素D（1,25D）和VDR能调节DTC细胞的分化和增殖，但它们的作用机制不明，我们假设1,25D能通过转录因子CCAAT增强子结合蛋白（C/EBPβ）抑制DTC细胞增殖，而VDR通过E-钙粘素信号系统抑制DTC细胞增殖并促进其分化。为了证明该假设，我们将下调乳头状和滤泡状甲状腺癌细胞内的C/EBPβ或E-钙粘素，观察1,25D和VDR是否还能影响癌细胞的分化、增殖和肿瘤生长。如能顺利完成这项研究，将能揭示1,25D及其受体调节DTC分化和增殖的机制，将有助于寻找新的DTC防治措施。

在项目资助下，我们探讨了C/EBPβ通路在1,25-双羟维生素D3【1,25(OH)2D3】抑制分化型甲状腺癌（DTC）中的作用。我们发现C/EBPβ介导1,25(OH)2D3的抑制DTC细胞增殖作用。并且1,25(OH)2D3促进DTC细胞p38MAPK信号通路磷酸化，从而上调磷酸化C/EBPβ的表达并增加细胞核内C/EBPβ的表达。我们还发现C/EBPβ上调Notch3的表达，抑制DTC细胞增殖。并且体内实验表明，下调C/EBPβ促进DTC移植瘤的生长。我们的结果表明，1,25(OH)2D3通过p38MAPK介导的信号通路诱导C/EBPβ磷酸化并发生核转位，从而靶向上调Notch3，最终抑制DTC细胞的增殖。我们还探讨了维生素D受体（VDR）在分化型甲状腺癌细胞增殖中的作用，我们发现，VDR抑制DTC细胞增殖，促进DTC细胞分化。而下调E-cadherin可以阻断过表达VDR的抑制增殖和促进分化作用，并且下调β-catenin可以逆转下调VDR的作用。进一步研究发现，VDR可以在细胞膜上结合E-cadherin和β-catenin，形成稳定复合物。体内实验表明，VDR抑制DTC移植瘤的生长。这些结果提示VDR通过稳定E-cadherin-β-catenin复合物抑制DTC增殖并促进其分化。并且，我们还发现p120对E-cadherin-β-catenin复合物在细胞膜上的稳定性起非常重要的作用。此外，维生素D缺乏在我国人群中的发生率很高，随着年龄的增大，人群合成1,25(OH)2D3的能力和VDR的含量下降，这些因素可能与人群中的甲状腺癌的发生发展有一定关系。本项目得出的结果证实了1,25(OH)2D3以及VDR调控DTC的作用机制，为甲状腺癌的防治提供了新的思路。