The Divergent Function of Androgen Receptor in Breast Cancer; Analysis of Steroid Mediators and Tumor Intracrinology

Androgen receptor (AR) is the most widely expressed steroid receptor protein in normal breast tissue and is detectable in approximately 90% of primary breast cancers and 75% of metastatic lesions. However, the role of AR in breast cancer development and progression is mired in controversy with evidence suggesting it can either inhibit or promote breast tumorigenesis. Studies have shown it to antagonize estrogen receptor alpha (ERα) DNA binding, thereby preventing pro-proliferative gene transcription; whilst others have demonstrated AR to take on the mantle of a pseudo ERα particularly in the setting of triple negative breast cancer. Evidence for a potentiating role of AR in the development of endocrine resistant breast cancer has also been mounting with reports associating high AR expression with poor response to endocrine treatment. The resurgence of interest into the function of AR in breast cancer has resulted in various emergent clinical trials evaluating anti-AR therapy and selective androgen receptor modulators in the treatment of advanced breast cancer. Trials have reported varied response rates dependent upon subtype with overall clinical benefit rates of ~19-29% for anti-androgen monotherapy, suggesting that with enhanced patient stratification AR could prove efficacious as a breast cancer therapy. Androgens and AR have been reported to facilitate tumor stemness in some cancers; a process which may be mediated through genomic or non-genomic actions of the AR, with the latter mechanism being relatively unexplored in breast cancer. Steroidogenic ligands of the AR are produced in females by the gonads and as sex-steroid precursors secreted from the adrenal glands. These androgens provide an abundant reservoir from which all estrogens are subsequently synthesized and their levels are undiminished in the event of standard hormonal therapeutic intervention in breast cancer. Steroid levels are known to be altered by lifestyle factors such as diet and exercise; understanding their potential role in dictating the function of AR in breast cancer development could therefore have wide-ranging effects in prevention and treatment of this disease. This review will outline the endogenous biochemical drivers of both genomic and non-genomic AR activation and how these may be modulated by current hormonal therapies.

Variants in estrogen biosynthesis genes, sex steroid hormone levels, and endometrial cancer: a HuGE review

Variants in genes involved in estrogen biosynthesis are likely to be important in the etiology of endometrial cancer. This review summarizes data on variants in seven genes in the estrogen biosynthesis pathway and their relation to circulating levels of sex steroid hormones in women and to risk of endometrial cancer. Little or no association was found between genotypes of the cytochrome P-450 genes CYP11A1 (-528[TTTTA]n) or CYP17A1 (-34T/C) or the 17beta-hydroxysteroid dehydrogenase 1 gene HSD17B1 (Ser312Gly) and levels of progesterone, androgens, or estrogens. The position -34T/C variant in CYP17A1 appears to be associated with reduced risk of endometrial cancer, with those homozygous for the variant allele having about half the risk of those homozygous for the wild type. Linked variants in CYP19A1 (intron 4 [TTTA]n, intron 4 [TCT] insertion/deletion, exon 10 C/T) are related to some hormone levels and, based on two studies, to risk of endometrial cancer. For other genes (HSD3B1, HSD3B2, HSD17B2), no information is available on these associations. Results indicate the need to study other variants and haplotypes in these genes, particularly CYP17A1 and CYP19A1, as well as variants in other genes involved in hormone biosynthesis and metabolism pathways. Larger studies or combined studies that allow for investigation of gene-gene and gene-environment interactions are warranted.

The post-menopausal ovary displays a unique pattern of steroidogenic enzyme expression

BACKGROUND

While menopause results in the loss of cyclic steroid production, evidence exists for persistent, albeit reduced, ovarian androgen production. In order to continue to synthesize ovarian androgens, the steroidogenic enzymes necessary for androgen biosynthesis must be present. Few studies have selectively analysed some of the steroidogenic enzymes present in the post-menopausal ovary (PMO), and a comprehensive study of this matter has never been undertaken.

METHODS

RNA and protein were obtained from PMO, pre-menopausal ovarian stroma, corpora lutea (CL), ovarian follicles, placenta, and myometrium. Oligonucleotide microarray analysis was performed to compare the gene expression profiles of PMO with pre-menopausal ovarian stroma. Real-time RT-PCR was performed for LH/HCG receptor (LHCGR), steroidogenic acute regulatory (StAR), cholesterol side-chain cleavage (CYP11A), 3beta-hydroxysteroid dehydrogenase type I (HSD3B1) and type II (HSD3B2, 3betaHSD), 17a-hydroxylase (CYP17), cytochrome b5 (CytB5), and aromatase (CYP19). Western blot analysis was performed for StAR, CYP11A, CYP17,and 3betaHSD.

RESULTS

The PMO and pre-menopausal ovarian stroma had a similar pattern of steroidogenic enzyme expression. The PMO had persistent, but reduced, levels of LHCGR and most steroidogenic enzymes. CYP19 and HSD3B2 mRNA were greatly reduced in PMO in comparison with CL (50-fold and 2000-fold less respectively). HSD3B2 was not detectable in PMO by western analysis.

CONCLUSIONS

This study supports the idea that the PMO retains some steroidogenic capacity. However, based on steroidogenic enzyme expression, the PMO has a unique pattern of steroidogenic enzyme expression that favors Delta5 steroid formation over Delta4 steroid formation.