TCDD Inhibition of Canonical Wnt Signaling Disrupts Prostatic Bud Formation in Mouse Urogenital Sinus

Abstract

In mice, in utero exposure to 2,3,7,8-tetrachlorodibenzo-p- dioxin (TCDD) reduces the number of dorsolateral prostatic buds resulting in a smaller dorsolateral prostate and prevents formation of ventral buds culminating in ventral prostate agenesis. The genes and signaling pathways affected by TCDD that are responsible for disrupting prostate development are largely unknown. Here we show that treatment of urogenital sinus (UGS) organ cultures with known inhibitors of canonical Wnt signaling also inhibits prostatic bud formation. In support of the hypothesis that TCDD decreases canonical Wnt signaling, we identify inhibitory effects of TCDD on multiple components of the canonical Wnt signaling pathway in the UGS that temporally coincide with the inhibitory effect of TCDD on prostatic bud formation: (1) expression of R-spondins (Rspo2 and Rspo3) that promote canonical Wnt signaling is reduced; (2) expression of Lef1, Tcf1, and Wif1, established canonical Wnt target genes, is decreased; (3) expression of Lgr5, a RSPO receptor that activates canonical Wnt signaling, is reduced; and (4) expression of Dickkopfs (Dkks), inhibitors of canonical Wnt signaling, is not increased by TCDD. Thus, the TCDD-induced reduction in canonical Wnt signaling is associated with a decrease in activators (Rspo2 and Rspo3) rather than an increase in inhibitors (Dkk1 and Dkk2) of the pathway. This study focuses on determining whether treatment of TCDD-exposed UGS organ cultures with RSPO2 and/or RSPO3 is capable of rescuing the inhibitory effects of TCDD on canonical Wnt signaling and prostatic bud formation. We discovered that each RSPO alone or in combination partially rescues TCDD inhibition of both canonical Wnt signaling and prostatic bud formation.

Combination effects of AHR agonists and Wnt/β-catenin modulators in zebrafish embryos: Implications for physiological and toxicological AHR functions

“…Thus, one interaction between AHR and Wnt signaling has been shown to involve AHR dependent effects on R-spondin levels (Mathew et al , 2008; Branam et al , 2013; Xu et al , 2013). Branam et al .…”

“…(2013) found that TCDD, like Wnt/β-catenin signaling inhibitors (including XAV), reduced the number of ventral prostatic buds in mouse embryos. This effect of TCDD was associated with a down-regulation of Wnt/β-catenin signaling and reduction in Rspo2 and Rspo3 mRNA levels, and addition of R-spondin 2 and 3 proteins partially rescued these effects of TCDD (Branam et al , 2013). In a recent study the same group showed that TCDD prevents the onset of β-catenin signaling in the ventral basal epithelium (Schneider et al , 2014b).…”

“…In male mouse fetuses prostatic budding is antagonized by TCDD apparently through Ahr-mediated down-regulation of R-spondins 2 and 3, associated with suppression of Wnt signaling (Branam et al , 2013). AHR activation by TCDD also triggers neuronal apoptosis in rat brain via down-regulation of Wnt/β-catenin signaling, and interferes with tissue regeneration in fin-amputated zebrafish via up-regulation of R-spondin 1 (Mathew et al , 2008; Xu et al , 2013).…”

FOXA1 and SOX9 Expression in the Developing Urogenital Sinus of the Tammar Wallaby <b><i>(Macropus eugenii)</i></b>

“…In contrast, FOXA1 was upregulated after day 51-60 in the male UGS, and thus may be negatively regulated by androgen, increasing once androstanediol levels fall, similar to the proliferative effects of SHH [Seifert et al, 2010;Chew et al, 2014]. Given the conservation of transcription factors FOXA1 and SOX9 expression and function between marsupials and eutherians, it is highly likely that other pathways such as Shh, Bmp and Wnt signalling, known to be critical for prostatic development [Miyazaki et al, 2000;Lamm et al, 2001Lamm et al, , 2002Freestone et al, 2003;Grishina et al, 2005;Branam et al, 2013;Schneider et al, 2014a, b], may also play a role in marsupial prostate morphogenesis.…”

“…Nkx3.1 is expressed in areas of the epithelium that will become prostatic buds [Sciavolino et al, 1997;Bhatia-Gaur et al, 1999]. A number of genes play pivotal roles in prostate morphogenesis including members of the hedgehog family (sonic hedgehog, SHH ) [Lamm et al, 2002;Freestone et al, 2003;Zhu et al, 2007], bone morphogenetic protein family (BMP4 and BMP7) [Miyazaki et al, 2000;Lamm et al, 2001;Grishina et al, 2005], and the canonical Wnt signalling pathway [Branam et al, 2013;Schneider et al, 2014a, b]. Two additional genes are essential for prostate development: forkhead box A1 (FOXA1) and SRY box-9 (SOX9) .…”