Kuo M T, Julian J, Husain F, Song R, Carson D D
Department of Molecular Pathology, University of Texas M.D. Anderson Cancer Center, Houston 77030, USA.
J Cell Physiol. 1995 Jul;164(1):132-41. doi: 10.1002/jcp.1041640117.
The mammalian uterine epithelium (UE) undergoes drastic physiological and morphological changes during pregnancy. Steady-state levels of murine mdr1b mRNA, transcribed from a multidrug resistance gene encoding a membrane protein which functions as a transporter of lipophilic cytotoxic agents, are low in nonpregnant, cycling UE, but drastically increase (about 1,500- to 2,000-fold) at day 8 of gestation. At day 16 of gestation, levels of mdr1b mRNA are 2,500- to 3,000-fold higher than those in the cycling UE cells. Levels of mdr1b mRNA were elevated to levels comparable to those observed during pregnancy, in the UE of ovariectomized mice following 5-8 days of estrogen and progesterone administration. Withdrawal of these hormones resulted in a drastic reduction of mdr1b mRNA within 36 hr. These results suggested that steroid hormones alone can account for increased mdr1b mRNA expression and do not require the presence of other placenta/embryo-derived factors. Moreover, the hormonal effect on uterine mdr1b mRNA biosynthesis during pregnancy apparently is a delayed phenomenon. Nuclear run-on assays demonstrated that the rate of mdr1b transcription in UE cells prepared from 15-day pregnant mice (d-15 UE cells) was about two- to three-fold higher than that in nonpregnant UE cells. This increased transcription rate alone cannot account for mdr1b mRNA accumulation during pregnancy. mdr1b mRNA expression was investigated in primary cultures of d-15 UE cells. mdr1b mRNA levels decayed by 50% within 3-4 hr of culture and reached a steady-state 0.5-2% of initial levels by 24 hr. The rate of mdr1b mRNA decay in primary d-15 UE cells was decreased by treatment with alpha-amanitin or cycloheximide, suggesting that the decay pathway requires both transcription and de novo protein synthesis. Our results suggest that multiple mechanisms are involved in the maintenance of the high levels of mdr1b mRNA in pregnant UE cells. Furthermore, these data suggest that increased mRNA stability may contribute to the accumulation of mdr1b transcript during pregnancy.
在妊娠期间，哺乳动物的子宫上皮（UE）会经历剧烈的生理和形态变化。小鼠mdr1b mRNA的稳态水平由一个多药耐药基因转录而来，该基因编码一种作为亲脂性细胞毒性剂转运蛋白的膜蛋白，在未怀孕、处于发情周期的UE中水平较低，但在妊娠第8天会急剧增加（约1500至2000倍）。在妊娠第16天，mdr1b mRNA的水平比处于发情周期的UE细胞高2500至3000倍。在给予雌激素和孕激素5 - 8天后，去卵巢小鼠的UE中mdr1b mRNA水平升高至与妊娠期间观察到的水平相当。停用这些激素会导致mdr1b mRNA在36小时内急剧减少。这些结果表明，仅甾体激素就能解释mdr1b mRNA表达的增加，且不需要其他胎盘/胚胎来源因子的存在。此外，妊娠期间激素对子宫mdr1b mRNA生物合成的影响显然是一种延迟现象。核转录分析表明，从妊娠15天的小鼠制备的UE细胞（d - 15 UE细胞）中mdr1b的转录速率比未怀孕的UE细胞高约两到三倍。仅这种增加的转录速率并不能解释妊娠期间mdr1b mRNA的积累。在d - 15 UE细胞的原代培养物中研究了mdr1b mRNA的表达。mdr1b mRNA水平在培养3 - 4小时内下降50%，到24小时时达到初始水平的0.5 - 2%的稳态。用α - 鹅膏蕈碱或环己酰亚胺处理可降低原代d - 15 UE细胞中mdr1b mRNA的降解速率，这表明降解途径需要转录和从头蛋白质合成。我们的结果表明，多种机制参与维持妊娠UE细胞中高水平的mdr1b mRNA。此外，这些数据表明，mRNA稳定性的增加可能有助于妊娠期间mdr1b转录本的积累。
