IS THERE A NEGATIVE TRE IN THE LUCIFERASE REPORTER CDNA

Transient expression assays using a luciferase (LUG) reporter gene are often used in studies of positive and negative thyroid hormone respon se elements (TREs) or of wild-type and mutated thyroid hormone recepto rs (TRs). However, unliganded TR (the beta isoform > than the alpha) i ncreases LUC expression from 2 different TK-LUC vectors in several cel l types, especially JEG-3 cells, and 3,5,3'-triiodothyronine (T-3) red uces that expression by as much as 80% in a TR-dependent manner. The T R effects require an intact TR DNA-binding domain and the results sugg est that there may be a negative TRE in the LUC cDNA. We conclude that great care must be used in the interpretation of studies of thyroid h ormone action using LUC expression plasmids especially when these are performed in JEG-3 cells.