Roman B L, Peterson R E
Environmental Toxicology Center, University of Wisconsin, Madison 53706, USA.
Toxicol Appl Pharmacol. 1998 Jun;150(2):240-53. doi: 10.1006/taap.1997.8362.
In utero and lactational 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure decreases rat prostate weight without decreasing circulating androgen concentrations. Because one mechanism by which TCDD is thought to cause toxicity is by aryl hydrocarbon receptor (AhR)-mediated alterations in gene transcription, the goals of this study were to determine whether the developing prostate expresses the AhR and its dimerization partner, the AhR nuclear translocator (ARNT); to determine whether in utero and lactational TCDD exposure is capable of directly activating gene transcription in the developing prostate; and to identify prostatic mRNAs that exhibit altered abundance in response to in utero and lactational TCDD exposure. Pregnant Holtzman rats were administered TCDD (1.0 microgram/kg po) or vehicle on Gestation Day (GD) 15, and male offspring were euthanized between Postnatal Days (PNDs) 1 and 63. Using reverse transcriptase-polymerase chain reaction (RT-PCR), mRNAs encoding the AhR and ARNT were detected in both ventral and dorsolateral prostates from control animals throughout postnatal development. ARNT protein was expressed in the majority of stromal nuclei early in development, whereas ARNT expression in the prostate epithelium was initially cytoplasmic but became nuclear as development progressed. GD 15 TCDD exposure increased cytochrome P4501A1 (CYP1A1) mRNA and protein in whole prostates between PNDs 7 and 21. In these TCDD-exposed animals, CYP1A1 protein was localized to the epithelium. In order to define other genes in the developing prostate that might be regulated by TCDD at the level of mRNA, RNA samples from PND 21 whole prostates from control and TCDD-exposed animals were compared using mRNA differential display. Although no growth-regulatory candidates were identified using this screening technique, a ventral prostate-specific, androgen-regulated mRNA (20-kDa protein) was identified that seemed to be downregulated by TCDD exposure. Northern blot analysis confirmed this decrease at PND 21 and further showed that the downregulation was transient. Similar results were obtained for four additional androgen-regulated prostatic mRNAs (prostatic binding protein [PBP], Royal Winnipeg Ballet [RWB], probasin, and dorsal protein-1 [DP-1]), all of which are markers of a differentiated ductal epithelium. In contrast, TCDD exposure of adult male rats (25 micrograms TCDD/kg, 24 h) greatly induced CYP1A1 mRNA without affecting the abundance of prostate-specific, androgen-regulated mRNAs. These results suggest that the transient decreases in androgen-regulated prostatic mRNA abundance observed in response to in utero and lactational TCDD exposure were probably not the result of direct action of the activated AhR on these genes but instead were reflective of a TCDD-induced delay in prostate development.
孕期和哺乳期暴露于2,3,7,8-四氯二苯并-对-二噁英（TCDD）会使大鼠前列腺重量减轻，而循环雄激素浓度却未降低。由于TCDD被认为引起毒性的一种机制是通过芳烃受体（AhR）介导的基因转录改变，本研究的目的是确定发育中的前列腺是否表达AhR及其二聚化伴侣AhR核转运蛋白（ARNT）；确定孕期和哺乳期TCDD暴露是否能够直接激活发育中前列腺的基因转录；并鉴定响应孕期和哺乳期TCDD暴露而丰度发生改变的前列腺mRNA。在妊娠第15天给怀孕的Holtzman大鼠经口给予TCDD（1.0微克/千克）或赋形剂，雄性后代在出生后第1天至63天之间实施安乐死。使用逆转录-聚合酶链反应（RT-PCR），在整个出生后发育过程中，从对照动物的腹侧和背外侧前列腺中均检测到编码AhR和ARNT的mRNA。ARNT蛋白在发育早期的大多数基质细胞核中表达，而前列腺上皮中的ARNT表达最初位于细胞质中，但随着发育进程变为细胞核表达。妊娠第15天暴露于TCDD使出生后第7天至21天整个前列腺中的细胞色素P4501A1（CYP1A1）mRNA和蛋白增加。在这些暴露于TCDD的动物中，CYP1A1蛋白定位于上皮细胞。为了确定发育中前列腺中可能在mRNA水平受TCDD调控的其他基因，使用mRNA差异显示比较了来自对照动物和暴露于TCDD动物的出生后第21天整个前列腺的RNA样品。尽管使用这种筛选技术未鉴定出任何生长调节候选基因，但鉴定出一种腹侧前列腺特异性、雄激素调节的mRNA（20 kDa蛋白），其似乎因TCDD暴露而下调。Northern印迹分析证实了出生后第21天的这种下调，并进一步表明这种下调是短暂的。另外四种雄激素调节的前列腺mRNA（前列腺结合蛋白[PBP]、皇家温尼伯芭蕾舞团蛋白[RWB]、前列腺素和背侧蛋白-1[DP-1]）也获得了类似结果，所有这些都是分化的导管上皮的标志物。相比之下，成年雄性大鼠暴露于TCDD（25微克TCDD/千克，24小时）可极大地诱导CYP1A1 mRNA，而不影响前列腺特异性、雄激素调节的mRNA的丰度。这些结果表明，响应孕期和哺乳期TCDD暴露而观察到的雄激素调节的前列腺mRNA丰度的短暂降低可能不是活化的AhR对这些基因直接作用的结果，而是反映了TCDD诱导的前列腺发育延迟。
