Teboul M, Bismuth J, Gharbi-Chihi J, Vallette A, Bonne J, Ghiringhelli O, Torresani J
INSERM U 38, Biochimie Médicale, Faculté de Médecine, Marseille, France.
Endocrinology. 1992 Mar;130(3):1475-82. doi: 10.1210/endo.130.3.1311241.
In the murine preadipocyte cell line Ob 17, T3 is known to be necessary at an early step of adipose differentiation for the expression of late phenotypes [lipogenic enzymes such as malic enzyme, glycerol-3-phosphate dehydrogenase (GPDH), etc.] and not necessary for the expression of lipoprotein lipase (LPL), which emerges earlier, at growth arrest. These cells contain nuclear T3 receptors, which mainly belong to products of the c-erbA alpha gene and are down-regulated by T3. In this work, retinoic acid (RA) added to Ob 17 cells at growth arrest impaired morphological differentiation and the development of both late (malic enzyme and GPDH) and early (LPL) phenotypes regardless of whether T3 was added. T3 sensitized the cells to the inhibitory action of RA; the ED50 for GPDH activity was shifted from 0.5 microM to 3 nM in cells cultured with 1.5 nM T3. Later addition of RA (6 days after growth arrest) did not inhibit the differentiation. RA also brought out a marked and fast decrease in nuclear T3 receptors. This was observed whatever the stage of cell development and related to both a rapid decrease in the relative abundance of c-erbA alpha-related mRNA species and an increased disappearance rate, suggesting the involvement of pre- and posttranslational events. RA and T3 acted additively in decreasing the T3 receptor and c-erbA alpha mRNA levels. The effects of RA on T3 receptors were rapidly reversed after RA withdrawal; the reversal was large (75%) when RA was introduced at growth arrest and total when introduced later. The cell sensitivity to RA, considering the T3 receptors, was higher at growth arrest (ED50 for RA, 0.2 and 1.5 microM in assays with RA added at growth arrest and 5 days later, respectively). The results suggest intricated regulatory pathways between RA and T3 at an early step of adipose differentiation and also suggest that among different mechanisms through which RA may impair this differentiation, a decreased level of nuclear T3 receptors at an early period should play a role.
在小鼠前脂肪细胞系Ob 17中，已知三碘甲状腺原氨酸（T3）在脂肪分化的早期阶段对于晚期表型（如苹果酸酶、甘油-3-磷酸脱氢酶（GPDH）等生脂酶）的表达是必需的，而对于脂蛋白脂肪酶（LPL）的表达则不是必需的，LPL在生长停滞时出现得更早。这些细胞含有核T3受体，其主要属于c-erbAα基因的产物，并受T3下调。在这项研究中，在生长停滞时添加到Ob 17细胞中的视黄酸（RA）损害了形态分化以及晚期（苹果酸酶和GPDH）和早期（LPL）表型的发育，无论是否添加T3。T3使细胞对RA的抑制作用敏感；在用1.5 nM T3培养的细胞中，GPDH活性的半数有效剂量（ED50）从0.5 μM变为3 nM。生长停滞6天后再添加RA不抑制分化。RA还导致核T3受体显著且快速减少。无论细胞发育阶段如何，均观察到这种情况，这与c-erbAα相关mRNA种类的相对丰度快速降低以及消失速率增加有关，提示翻译前和翻译后事件均参与其中。RA和T3在降低T3受体和c-erbAα mRNA水平方面具有相加作用。RA撤除后，RA对T3受体的作用迅速逆转；在生长停滞时引入RA时逆转幅度较大（75%），后期引入时则完全逆转。考虑到T3受体，细胞在生长停滞时对RA的敏感性更高（在生长停滞时添加RA和5天后添加RA的试验中，RA的ED50分别为0.2和1.5 μM）。结果提示在脂肪分化的早期阶段，RA和T3之间存在复杂的调控途径，并且还表明在RA可能损害这种分化的不同机制中，早期核T3受体水平降低应起作用。
