The Androgen Regulation of the Prostate-Specific TMPRSS2 Gene Is Subject to Genetic Variation

Presentation Number: MON-0382
Date of Presentation: June 23rd, 2014

Frank A. Claessens*, Thomas Van Den Broeck, Liesbeth Clinckemalie and Steven Joniau
KU Leuven, Leuven, Belgium

Abstract

The androgen, progesterone, mineralocorticoid and glucocorticoid receptors (AR, PR, MR and GR) share very similar DNA-binding domains (DBD) and bind to very similar DNA elements in the genome. In fact, their consensus sequences are nearly identical. And yet, the AR has a more relaxed DNA sequence-specificity which correlates with a stronger dimerization interface in the second zinc finger of the DBD. Of course, AR, PR, MR and GR have different target genes, so other mechanisms besides DNA selectivity must lead to the specificity of the hormone responses.

While approximately half of all prostate cancers harbor a genomic reorganization which puts the expression of ERG under control of the androgen-regulated and prostate-specific TMPRSS2 promoter, the exact consequences of the ERG overexpression remains obscure. The androgen-dependency of prostate cancer is its Achilles’ heel: AR antagonists have been successfully used to prolong life, even of patients with metastatic, castration-resistant forms. Therefore, here we studied the androgen regulation of the TMPRSS2 gene.

We performed DNaseI footprinting, electrophoretic mobility shift assays (EMSA), transfection assays and mutation analyses of plasmid constructs and bacterial artificial chromosomes (BAC). These all pointed at a crucial androgen-dependent enhancer at -13 kb upstream of the TMPRSS2 transcription start site. This enhancer encompasses a high affinity binding site for the AR, three adjacent binding sites for GATA-2 and one overlapping binding site for Oct1 at the site where others have clearly shown AR binding by chromatin immunoprecipitation (Wang Q et al. Mol Cell 2007). The ARE was called TMPRSS2-ARE2 to distinguish it from the in silico predicted ARE which was not active in our analyses.

Not surprisingly, the AR- and GR-DBD bind the TMPRSS2-ARE2 with similar affinities. Moreover, a Single Nucleotide Polymorphism (SNP) resides in this ARE, affecting AR binding and transactivation as measured in EMSA and BAC constructs. We found this SNP in approximately 10% of prostate cancer patients and will now determine its effect on ERG expression in fusion positive prostate cancers.

 

Nothing to Disclose: FAC, TV, LC, SJ