A simple enzyme-linked immunosorbent assay for sex hormone-binding globulin.

A simple enzyme-linked immunosorbent assay (ELISA) for sex hormone-binding globulin (SHBG) has been developed. Polyclonal antibody raised to SHBG purified to homogeneity was employed. The ELISA, which may be performed in under 4 h, shows no cross-reactivity with other serum proteins, has a sensitivity of less than 1.2 fmol per sample, demonstrates excellent correlation with ligand-binding techniques (r = 0.996; p less than 0.0001), and has intra- and inter-assay coefficients of variation of between 5-9% and 7-11% respectively.

Evidence for a novel binding site for the synthetic progestogen, gestodene on oestrogen receptor in human malignant tissue.

The binding of the synthetic progestogen, 17 alpha-ethinyl-13 beta-ethyl-17 beta-hydroxy-4,15-gonadiene-3-one (gestodene) to estrogen receptor (ER) in malignant breast disease is refractory to competition by excess amounts of estra-1,3,5 (10)-triene-3,17 beta-diol (estradiol, E2) or tamoxifen, whereas gestodene in excess amounts can reduce the E2 binding sites by 31-44% and increase the Ka 2-3 times. Given the close similarity of the number of binding sites measured by E2 or gestodene and the similarity of dissociation constants, we propose that in the already altered ER of the malignant human breast there is another binding site for gestodene which closely approximates in number and affinity the binding site for E2, and that gestodene itself is capable of bringing about a configurational change which greatly reduces the binding of E2 to ER without completely abolishing it.

Mechanisms of sex-steroid accumulation in the aetiology of human breast carcinoma: the role of intracellular sex hormone binding globulin.

In malignant breast tissue cytosols (n = 14), significantly high levels of oestradiol (E2), testosterone and 5a-dihydrotestosterone (DHT) and sex hormone binding globulin (SHBG) were found as compared to breast tissue cytosols from normal women (n = 12) (p less than 0.001 for all parameters measured). In serum from the same patients and normal control groups no differences in these hormones or SHBG were detected, nor was relationship between serological and cytosolic levels observed. In the cytosol of the malignant group there was a significant correlation between testosterone and DHT, r = 0.98, p less than 0.001. This was also the case in the cytosol of normal breast tissue, r = 0.97, p less than 0.001. No such correlation between the two androgens was observed in the sera of either group. We hypothesise that the malignant breast is able to regulate its own hormonal milieu and that the nearly 8 times higher levels of intracellular SHBG compared to those in normal breast cytosol may be one the factors responsible for this accumulation of sex-steroids. In addition, SHBG due to its higher affinity for androgens than for E2 may shift the balance in favour of free oestrogens in malignant breast tissue.

Sex-steroid receptors in human breast cancer. Incidence and interrelationships.

Over-expression of oestrogen and progesterone receptor (ER and PR respectively) has been reported in malignant breast disease but the techniques employed have been relatively insensitive and prone to underestimations. Using a highly sensitive microassay method, we have estimated ER (n = 39), PR (n = 32) and androgen receptor (AR) (n = 37) in cytosolic and nucleosolic fractions obtained from the same tissue samples. Induction of PR by oestrogen is a widely recognized phenomenon, and a relationship between PR and ER is to be expected. There is evidence that sex-steroids and their receptors act in concert and it is therefore surprising that AR has been poorly studied in malignant breast disease, despite indications that its presence increases hormone responsiveness. Our hypothesis is that, unlike the normal breast, in malignancy a possible deregulation of transcriptional control may lead to an over expression of all three classes of sex-steroid receptor. Using the microassay, we have tested this hypothesis and found not only a greater incidence of ER, AR and PR than previously reported in malignant breast disease, but considerably higher levels of these receptors. In addition, our findings demonstrate that these receptors tend to be expressed simultaneously rather than discretely, supporting the view that a deregulation of transcriptional control may account for the clinical and biological heterogeneity of the disease.

Sex-steroid receptors and cancer--are we on the right tracks? (Review).

Despite the overemphasis on sex-steroid receptors in cancer, the latter remains a multifactorial process. Many hypotheses have been put forward for the interaction of steroids with receptors but relatively little attention has been paid to other binding components, e.g., antioestrogen binding sites, intracellular sex hormone binding globulin, calcium-calmodulin, protein kinases and other receptor-independent phenomena, which may be pertinent to malignancy and are reviewed in this article.