Handwerger S, Myers S, Richards R, Richardson B, Turzai L, Moeykins C, Meyer T, Anantharamahiah G M
Division of Endocrinology, Children's Hospital Medical Center, Cincinnati, Ohio 45229-3039, USA.
Endocrinology. 1995 Dec;136(12):5555-60. doi: 10.1210/endo.136.12.7588308.
Earlier studies from our laboratory indicated that apolipoprotein A-I (Apo A-I) stimulates the acute release of human placental lactogen (hPL) from trophoblast cells in culture. We have now demonstrated that Apo A-I also causes a secondary increase in hPL release, beginning about 6 h after exposure to Apo A-I, that is blocked by cycloheximide and actinomycin D. Apo A-I also stimulated a dose-dependent increase in hPL promoter activity in JAR cells transfected with a 1.1-kilobase (-1078/2) fragment of the hPL3 promoter coupled to a chloramphenicol acetyltransferase (CAT) reporter gene. Maximal stimulation, 5.2-fold above basal levels, occurred at an Apo A-I concentration of 1.5 mg/ml, which is within the physiological concentration of Apo A-I during pregnancy. 37pA, a synthetic amphipathic peptide that mimics the secondary structure of Apo A-I and stimulates the synthesis and release of hPL, also stimulated a dose-dependent increase in CAT activity, with maximal stimulation comparable to that caused by Apo A-I. In addition, Apo A-I stimulated a modest increase in CAT activity in BeWo choriocarcinoma cells, Chinese hamster ovary cells, and HeLa cells. However, the maximal stimulation of hPL promoter activity in the Chinese hamster ovary and HeLa cells (approximately 2.5-fold above basal levels) was less than that in choriocarcinoma cells, suggesting that trophoblast cell nuclear factors may be necessary for maximal expression of the promoter in response to Apo A-I. Taken together, these results indicate that Apo A-I stimulates hPL gene expression, and that DNA elements in the first 1.1 kilobase of the promoter are sufficient for transactivation by Apo A-I.
我们实验室早期的研究表明，载脂蛋白A-I（Apo A-I）可刺激培养的滋养层细胞急性释放人胎盘催乳素（hPL）。我们现在已经证明，Apo A-I还会导致hPL释放的二次增加，在接触Apo A-I约6小时后开始，这种增加被放线菌酮和放线菌素D阻断。Apo A-I还刺激了用与氯霉素乙酰转移酶（CAT）报告基因偶联的hPL3启动子的1.1千碱基（-1078/2）片段转染的JAR细胞中hPL启动子活性的剂量依赖性增加。在Apo A-I浓度为1.5 mg/ml时出现最大刺激，比基础水平高5.2倍，这在怀孕期间Apo A-I的生理浓度范围内。37pA是一种模拟Apo A-I二级结构并刺激hPL合成和释放的合成两亲性肽，也刺激了CAT活性的剂量依赖性增加，最大刺激与Apo A-I引起的刺激相当。此外，Apo A-I刺激了BeWo绒毛膜癌细胞、中国仓鼠卵巢细胞和HeLa细胞中CAT活性的适度增加。然而，中国仓鼠卵巢细胞和HeLa细胞中hPL启动子活性的最大刺激（比基础水平高约2.5倍）低于绒毛膜癌细胞中的刺激，这表明滋养层细胞核因子可能是启动子响应Apo A-I最大表达所必需的。综上所述，这些结果表明Apo A-I刺激hPL基因表达，并且启动子前1.1千碱基中的DNA元件足以被Apo A-I反式激活。
