Searchable abstracts of presentations at key conferences in endocrinology
Endocrine Abstracts (2011) 26 S26.1

ECE2011 Symposia The role of plasma binding proteins in tissue hormone delivery (3 abstracts)

Sex hormone-binding globulin: beyond plasma transport

G Hammond 1,


1Child and Family Research Institute, Vancouver, British Columbia, Canada; 2University of British Columbia, Vancouver, British Columbia, Canada.


Sex hormone-binding globulin (SHBG) transports sex steroids (androgens and estrogens) in the blood and regulates their access to tissues. In humans and other vertebrates, the liver produces the SHBG that circulates in the blood, and in most species the gene encoding SHBG is also expressed in the testis. The testicular cell types in which SHBG is produced vary between species; in most mammals, expression of the Shbg gene in Sertoli cells gives rise to a secreted protein that binds androgens in the seminiferous tubules and male reproductive tract. By contrast, the human SHBG gene is expressed in developing sperm cells rather than Sertoli cells. In spermatids and spermatozoa, human SHBG accumulates as an amino-terminally truncated isoform in the acrosome, the concentrations of which decrease with aging and are correlated with sperm motility. Studies in transgenic mice have indicated that human SHBG is also produced as distinct glycoforms in several other tissues, and accumulates inside sex steroid-sensitive cells of the kidney and small intestine. The physiological role(s) of these intracellular forms of SHBG remain to be established, but recent studies indicate that intracellular SHBG may influence the access of sex-steroids to the respective receptors and the response of sex steroid-target genes. In addition, immunoreactive SHBG has been located in the extra-vascular compartments of some tissues, where it has been reported to interact with proteins in the cell membrane, which are thought to act as endocytotic receptors, such as megalin; signaling receptors which remain to be identified; or proteins in the extra-cellular matrix, such as fibulin, with which SHBG interacts in a ligand dependent manner. These novel activities and functions of SHBG will be reviewed because they provide evidence that SHBG has activities beyond that of a simple plasma steroid transport protein.

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