IN-UTERO AND LACTATIONAL EXPOSURE OF THE MALE-RAT TO 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN IMPAIRS PROSTATE DEVELOPMENT - 1 - EFFECTS ON GENE-EXPRESSION

In utero and lactational 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) ex posure decreases rat prostate weight without decreasing circulating an drogen concentrations. Because one mechanism by which TCDD is thought to cause toxicity is by aryl hydrocarbon receptor (AhR)-mediated alter ations in gene transcription, the goals of this study were to determin e whether the developing prostate expresses the AhR and its dimerizati on partner, the AhR nuclear translocator (ARNT); to determine whether in utero and lactational TCDD exposure is capable of directly activati ng gene transcription in the developing prostate; and to identify pros tatic mRNAs that exhibit altered abundance in response to in utero and lactational TCDD exposure. Pregnant Holtzman rats were administered T CDD (1.0 mu g/kg po) or vehicle on Gestation Day (GD) 15, and male off spring were euthanized between Postnatal Days (PNDs) 1 and 63. Using r everse transcriptase-polymerase chain reaction (RT-PCR), mRNAs encodin g the AhR and ARNT were detected in both ventral and dorsolateral pros tates from control animals throughout postnatal development. ARNT prot ein was expressed in the majority of stromal nuclei early in developme nt, whereas ARNT expression in the prostate epithelium was initially c ytoplasmic but became nuclear as development progressed. GD 15 TCDD ex posure increased cytochrome P4501A1 (CYP1A1) mRNA and protein in whole prostates between PNDs 7 and 21. In these TCDD-exposed animals, CYP1A 1 protein was localized to the epithelium. Zn order to define other ge nes in the developing prostate that might be regulated by TCDD at the level of mRNA, RNA samples from PND 21 whole prostates from control an d TCDD-exposed animals were compared using mRNA differential display. Although no growth-regulatory candidates were identified using this sc reening technique, a ventral prostate-specific, androgen-regulated mRN A (20-kDa protein) was identified that seemed to be downregulated by T CDD exposure. Northern blot analysis confirmed this decrease at PND 21 and further showed that the downregulation was transient. Similar res ults were obtained for four additional androgen-regulated prostatic mR NAs (prostatic binding protein [PBP], Royal Winnipeg Ballet [RWB], pro basin, and dorsal protein-1 [DP-1]), all of which are markers of a dif ferentiated ductal epithelium, In contrast, TCDD exposure of adult mal e rats (25 mu g TCDD/kg, 24 h) greatly induced CYP1A1 mRNA without aff ecting the abundance of prostate-specific, androgen-regulated mRNAs. T hese results suggest that the transient decreases in androgen-regulate d prostatic mRNA abundance observed in response to in utero and lactat ional TCDD exposure were probably not the result of direct action of t he activated AhR on these genes but instead were reflective of a TCDD- induced delay in prostate development. (C) 1998 Academic Press.