Expression of nuclear hormone receptors, their coregulators and type I iodothyronine 5′-deiodinase gene in mammary tissue of nonlactating and postlactating rats

The aim of the study was to test the hypothesis that expression of retinoid receptors (RARα, RARβ, RARγ), rexinoid receptors (RXRα, RXRβ), thyroid hormone receptors (TRα, TRβ), estrogen receptors (ERα, ERβ), nuclear receptor coregulators (N-CoR, SRC-1, SMRT), and in addition type I iodothyronine 5′-deiodinase (5′-DI), EGFR and erb-B2/neu would be different in mammary postlactating tissue in comparison with that of nonlactating mammary gland. Using RT-PCR, we have shown that expression of RARα, RXRα, TRα, ERα, ERβ, N-CoR, SRC-1, SMRT and EGFR in rat was significantly increased in postlactating mammary gland when compared to that of nonlactating mammary tissue. Postlactating mammary glands were found to express all RAR and RXR subtypes studied when compared to nonlactating mammary tissues that express exclusively RARα and RXRα subtypes. Enhanced expression of a number of nuclear hormone receptors, their coregulators in mammary tissue of postlactating rats in comparison with nonlactating animals identify a potential role for retinoid, thyroid and estrogen signalling pathways also after lactation period.