Sex hormone binding globulin of the plasma: Towards understanding of a new regulatory system in steroid hormone action

Abstract

Sex hormone binding globulin (SHBG) is a protein that circulates in the plasma of many species and binds with high affinity to sex steroids in the human and primates, while it is androgen-binding protein in many animals including sheep, dog, rabbit etc. Its expression is regulated by many hormones and recent evidence has shown that steroids regulate SHBG expression in a species-specific manner. Studies from our laboratory have shown that estrogen binds to SHBG in a non-linear fashion emphasizing the importance of evaluation of SHBG levels in various conditions. The cell membrane SHBG receptor presence in various steroid dependent tissues revealed that SHBG may play an important role in cellular proliferation in those tissues. The present study discusses the recent theories and findings regarding the biological role of SHBG.