Contact information
Bradley.E.Gillesby@sb.com

Current Position
Research scientist, Smithkline Beecham, Oakville, Ontario, Canada

Dissertation

Breast Cancer Prognostic marker, pS2, and Its Regulation by Dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and related compounds modulate several endocrine systems by enhancing ligand metabolism, down-regulating estrogen receptors/binding activity, and altering gene expression. TCDD was found to inhibit 17b-estradiol (E2)-induction of pS2, a human breast cancer prognostic marker, through an Ah receptor (AhR)-mediated mechanism at the gene expression level. Analysis of the pS2 5'-regulatory region identified a motif between positions -522 to -513 require for TCDD-mediated antiestrogenicity. This sequence contained the conserved dioxin response element (DRE) core sequence but varied in the flanking nucleotides. Reversion of this imperfect DRE-like motif to the consensus DRE sequence had little effect on TCDD's ability to suppress E2-induced pS2-regulated luciferase reporter gene activity, although it did improve AhR complex binding to the DRE-like motif in vitro. Further study of this region also revealed an adjacent putative AP-1 site capable of binding a TPA-induced complex. Mutation of this AP-1 like motif greatly diminished E2-inducibility suggesting that an interaction between AhR complexes and AP-1 like proteins may be responsible for TCDD-mediated inhibition of E2-induced pS2 expression.

The expression of pS2 has been previously shown to identify patients with improved response to anti-hormonal therapy and more favorable outcome. In the current study, 100 human breast carcinoma samples were analyzed for pS2 mRNA using a quantitative, competitive reverse transcriptase-polymerase chain reaction (qcRT-PCR) assay. pS2 mRNA levels were positively associated with both ER and PR, with the majority of ER+ (59%) and PR+ (60%) tumors also being positive for pS2. In addition, a significant linear correlation was observed between the amount of pS2 mRNA and ER (p<0.0001) and PR (p<0.0001) protein. pS2 mRNA levels also exhibited an inverse association with tumor size and histological grade. No associations were observed with tumor cell type, patient age, or lymph node status. The strong correlation displayed between pS2 and a number of currently used breast cancer prognostic markers supports the clinical use of pS2 to further assess tumor status and patient outcome.