Identification of albumin in breast tumor cytosol as a factor involved in the stimulation of estradiol 17 beta-hydroxysteroid dehydrogenase (reductive) activity.

Estradiol 17 beta-hydroxysteroid dehydrogenase (E2DH) is the enzyme responsible for the interconversion of estrone (E1), and the more biologically potent steroid, estradiol (E2), and has a crucial role in regulating breast tissue concentrations of E2. It has previously been shown that breast tumor cytosol is able to preferentially stimulate the reductive conversion of E1 to E2 in cultured MCF-7 breast cancer cells. In this study the stimulatory factor(s) from breast tumor cytosol have been partially purified by gel filtration and affinity chromatography. Human serum albumin (HSA) has been identified as a component of this bioactive fraction. Subsequent testing of commercially purified HSA preparations has revealed the ability of some preparations to be highly stimulatory. The albumin present in breast tumor cytosol may therefore be a contributing factor to the observed stimulation of reductive E2DH activity in cultured MCF-7 cells. Such a mechanism may account in part for the higher concentrations of E2 which are observed in breast tumors in vivo.