2,3,7,8-Tetrachlorodibenzo-p-dioxin Blocks Androgen-Dependent Cell Proliferation of LNCaP Cells through Modulation of pRB Phosphorylation

Abstract

Cell-cycle regulatory events associated with inhibition of androgen-dependent cell proliferation by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were studied in the human-derived LNCaP cell line. TCDD blocked the G 1 to S transition of LNCaP cells synchronized in G 0 /G 1 when these cells were induced to reinitiate cell-cycle progression by dihydrotestosterone (DHT). Western blot analyses of these cells revealed altered expression levels of G 1 regulatory proteins, including increases in hypophosphorylated retinoblastoma protein and concomitant decreases in cyclin D1. p21 WAF1/CIP1 , which is involved in the assembly of cyclin D1/cyclin-dependent kinase-4 complexes, was increased by DHT or TCDD when each compound was administered singly but was reduced to background levels in cells simultaneously treated with DHT and TCDD. Reporter gene assays revealed the presence of several Ah receptor response-element motifs in the promoter and first intron of the p21 WAF1/CIP1 gene that respond to TCDD-mediated Ah receptor activation independently of p53. Transcription studies showed that activation of aryl hydrocarbon receptor blocks androgen-dependent gene induction in LNCaP cells as well as in African green monkey CV-1 cells. These data point to at least two mechanisms whereby TCDD blocks androgen receptor function: 1) by blocking androgen-induced cell proliferation through modulation of the expression and activities of regulatory proteins controlling cell-cycle progression; and 2) by squelching androgen receptor-mediated gene transcription through receptor cross-talk, possibly involving competition for coregulators or by direct protein interaction.Depending on cell type and lineage, exposure to TCDD often leads to multiple diverse responses, including changes in cell proliferation and differentiation. Most, if not all, of the effects of TCDD are mediated through binding to a ligandactivated transcription factor known as the Ah receptor. In brief, TCDD binds to the AHR and facilitates the release of bound 90-kDa heat-shock proteins, resulting in receptor activation. Subsequent to this release, liganded AHR translocates to the nucleus, in which it heterodimerizes with ARNT.

Sustained Aryl Hydrocarbon Receptor Activity Attenuates Liver Regeneration

“…Kip1 (Kolluri et al, 1999;Barnes-Ellerbe et al, 2004). The present findings demonstrate that TCDD treatment suppresses BrdU incorporation in the regenerating liver, suggesting that prolonged AhR activation can impair cell cycle progression into S phase and commitment to cell division.…”

Pax3 and Pax7 Play Essential Safeguard Functions against Environmental Stress-Induced Birth Defects

“…Transcripts levels for Ahr and its direct target genes, including Aldh1a3, a gene coding for an enzyme involved in retinoic acid production and nasal process development (Dupé et al, 2003;Hankinson, 1995) and p21 (Cdkn1a, cyclin-dependent kinase inhibitor 1A), a mediator of cell-cycle exit and growth arrest (Barnes-Ellerbe et al, 2004;Besson et al, 2008), were higher in Pax3 Pax3-ERD/GFP CNCC ( Figure 3B). Consistently, we detected a specific upregulation of AHR protein in the nasal process mesenchyme and epithelium in both E10.5 and E11.5 Pax3 Pax3-ERD/GFP embryos compared to control (Figures 3C and S4).…”

Aryl hydrocarbon receptor, cell cycle regulation, toxicity, and tumorigenesis

“…In mouse intrathymic progenitor cells, TCDD blocked Sphase progression and caused persistent thymic atrophy [Laiosa et al, 2003]. TCDD also inhibited proliferation of the fish hepatocellular carcinoma PLHC-1 cell line [Hestermann et al, 2002] and the androgen-induced proliferation of G 0 /G 1 -synchronized human prostate cancer LNCaP cells [Barnes-Ellerbe et al, 2004]. Treatment with TCDD also induced the AHRdependent G 1 arrest of SK-N-SH human neuronal cells concomitant with the increased expression of p27 and the hypophosphorylation of RB [Jin et al, 2004].…”