Biomedical subjects
Publications and source records attributed to E F Hawkins.
Recent studies on the eukaryotic nucleus have described the presence of a structural component termed the nuclear matrix, that appears to be involved in nucleic acid synthesis. This study will present evidence that the nuclear matrix of both the rat uterus and chick liver contains specific, high affinity, saturable estradiol binding sites.
The potent synthetic androgen methytrienolone (R 1881), which does not bind to serum proteins, was utilized to characterize binding to receptors in human androgen responsive tissues. Cytosol extracts prepared from hypertrophic prostates (BPH) were utilized as the source of receptor for the initial studies. High affinity binding was detected in the cytosol of 29 of 30 samples of BPH (average number of binding sites, 45.8+/-4.7 fmol/mg of protein; dissociation constant, 0.9+/-0.2 nM). This binding had the characteristics of a receptor: heat lability, precipitability by 0-33% ammonium sulfate and by protamine sulfate, and 8S sedimentation coefficient. High affinity binding was also detected in cytosol prepared from seminal vesicle, epididymis, and genital skin but not in non-genital skin or muscle. However, similar binding was demonstrated in the cytosol of human uterus. The steroid specificities of binding to the cytosol of male tissues of accessory reproduction and of uterus were similar in that progestational agents were more effective competitors than natural androgens. Binding specificities in cytosol prepared from genital skin were distinctly different and were similar to those of ventral prostate from the castrated rat in that dihydrotestosterone was much more potent than progestins in competition. Thus binding of R 1881 to the cytosol of prostate, epididymis, and seminal vesicle has some characteristics of binding to a progesterone receptor. When the nuclear extract from BPH was analyzed, high affinity binding was demonstrated that conformed to the specificities of binding to an androgen receptor. Here dihydrotestosterone was a more potent competitor than progestational agents. Similar patterns of binding were detected in the crude nuclear extracts from seminal vesicle, epididymis, and genital skin but not in uterus, muscle, or non-genital skin. We conclude that the androgen receptor is not demonstrable in the cytosol of prostate, epididymis, or seminal vesicle of non-castrated men but can be measured in the cytosol of genital skin and the nuclear extracts of androgen responsive tissues. Because steroid hormones exert their major influence within the nucleus of target tissues, the measurement of nuclear receptor may provide valuable insight into the regulation of growth of target tissues.
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We have searched for tissue-specific binding of 5alpha-androstan-17beta-ol-3-one (5alpha-dihydrotestosterone; 5alpha-DHT) in cytosols prepared from 25 surgically obtained benign prostatic hypertrophy (BPH) samples and in 3 tissue specimens containing prostate cancer cells. The distinction between steroid-receptor complexes and ligand binding to serum sex hormone-binding globulin (SHBG) was facilitated by combination experiments involving both sucrose gradient ultracentrifugation and agar gel electrophoresis. Gradient analysis of a cytosol prepared from a cervical lymph node (CLN) containing metastatic prostate tissue, revealed both 8-S and 4-S forms of high affinity (charcoal stable) 5alpha-[3H]DHT binding. When electrophoresis was performed on gradient fractions from these zones, anodally migrating steroid-receptor complexes were found only in the 8-S peak, the 4-S region containing radioligand bound to cathodally directed SHBG. In similar experiments with two BPH samples heavily invaded with prostate cancer cells only a single 4-S peak of radioligand binding was detected. Its multicomponent nature was uncovered electrophoretically when, in addition to SHBG, saturable, androgen binding molecules appeared anodally. Their incomplete resolution from SHBG on a gradient might have prevented their identification had this been the only method used. In contrast to the cancer-containing tissues, no saturable 5alpha-[3H]-DHT binding, other than that to SHBG, was detected in any of the BPH samples analysed. It is considered that, of the methods currently available, agar gel electrophoresis may be particularly useful for further investigations into the possible multicomponent nature of androgen binding of tissue origin in the human prostate.
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Explore the source record for details and available documents.
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Agar gel electrophoresis and ultracentrifugation on continuous sucrose gradients revealed the presence of a 4S estradiol 'receptor' in cytosols of samples of human benign hyperplastic prostate tissue. High affinity (charcoal stability) and saturability (disappearance with excess competitor) binding characteristics of the molecular species concerned facilitated its clear distinction from similarly migrating serum albumin-steroid complexes. Our data, obtained with human serum, purified human albumin and albumin-enriched cytosol strongly suggest that agar gel electrophoresis, when used alone, may lack specificity for the quantification of estrogen 'receptors'. Radioligand binding to these molecules may be obscured by similarly migrating albumin-steroid complexes which fail to dissociate during electrophoresis. We advocate the inclusion of competitor experiments to improve the specificity of the method.