Yu Zengli, Lin Jiuxiang, Xiao Ying, Han Jing, Zhang Xingzhong, Jia Haichao, Tang Yunan, Li Yong
School of Stomatology, Peking University, Beijing, 100081, China; School of Public Health, Peking University, Beijing, 100083, China.
Toxicol Sci. 2005 Feb;83(2):349-54. doi: 10.1093/toxsci/kfi030. Epub 2004 Nov 10.
all-trans retinoic acid (atRA), the oxidative metabolite of vitamin A, is essential for normal embryonic development. Also, high levels of atRA are teratogenic in many species and can effectively induce cleft palate in the mouse. Most cleft palate resulted from the failed fusion of secondary palate shelves, and maintenance of the normal cell proliferation is important in this process of shelf growth. To clarify the mechanism by which atRA causes cleft palate, we investigated the effect of atRA on proliferation activity and cell cycle distribution in mouse embryonic palatal mesenchymal (MEPM) cells. atRA inhibited the growth of MEPM cells by inducing apoptosis in a dose-dependent manner. atRA also caused a G1 block in the cell cycle with an increase in the proportion of cells in G0/G1 and a decrease in the proportion of cells in S phase, as determined by flow cytometry. We next investigated the effects of atRA on molecules that regulate the G1 to S phase transition. These studies demonstrated that atRA inhibited expression of cyclins D and E at the protein level. Furthermore, atRA treatment reduced phosphorylated Rb and decreased cdk2 and cdk4 kinase activity. These data suggest that atRA had antiproliferative activity by modulating G1/S cell cycle regulators and by inhibition of Rb phosphorylation in MEPM cells, which might account for the pathogenesis of cleft palate induced by retinoic acid.
全反式维甲酸（atRA）是维生素A的氧化代谢产物，对正常胚胎发育至关重要。此外，高剂量的atRA在许多物种中具有致畸性，并且能有效诱导小鼠腭裂。大多数腭裂是由于继发腭突未能融合所致，而在腭突生长过程中维持正常细胞增殖很重要。为了阐明atRA导致腭裂的机制，我们研究了atRA对小鼠胚胎腭间充质（MEPM）细胞增殖活性和细胞周期分布的影响。atRA通过以剂量依赖的方式诱导细胞凋亡来抑制MEPM细胞的生长。通过流式细胞术测定，atRA还导致细胞周期中的G1期阻滞，G0/G1期细胞比例增加，S期细胞比例减少。接下来，我们研究了atRA对调节G1期到S期转变的分子的影响。这些研究表明，atRA在蛋白质水平上抑制细胞周期蛋白D和E的表达。此外，atRA处理降低了磷酸化Rb水平，并降低了cdk2和cdk4激酶活性。这些数据表明，atRA通过调节MEPM细胞中的G1/S细胞周期调节因子以及抑制Rb磷酸化而具有抗增殖活性，这可能解释了维甲酸诱导腭裂的发病机制。
