A cytosolic binding protein for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the uterus and deciduoma of rats.

The cytosol fraction of the uterus of proestrous rats and of deciduoma specifically binds 3H-2,3,7,8-tetrachlorodibenzo-p-dioxin (3H-TCDD). The 3H-TCDD binding protein has a sedimentation coefficient of 9 S in low ionic 10-40% sucrose density gradients. The binding of 3H-TCDD in the 9 S region is abolished by a 500-fold molar excess of unlabeled benzo[a]pyrene, 3-methylcholanthrene or by a 100-fold molar excess of unlabeled TCDD. Incubation of the binding protein with TCDD in amounts in excess of 500 nM causes aggregation of the TCDD binding protein. Neither estradiol, progesterone, testosterone, dihydrotestosterone nor cortisol competed with TCDD in binding to this 9 S protein. The decidual tissue contains two binding components for TCDD as shown by Scatchard analysis. One of the components has a high affinity for TCDD (Kd = 1.68 nM) and is saturable. The number of binding sites is about 75 fmol/mg protein. The TCDD binding protein eluted through a DEAE-cellulose column using a gradient of 0.25 M KCl. The binding of estradiol and progesterone to their respective receptors was not affected by TCDD or by other polycyclic aromatic hydrocarbons as shown by sucrose density gradients and by microtiter competition assays. These results suggest that TCDD acts by binding to its own receptor system in the target tissue and not by competing with estrogen or progesterone for binding to their receptors. The possible role of the receptor in teratogenesis is discussed.