PROMOTER INDEPENDENT DOWN-REGULATION OF THE FIREFLY LUCIFERASE GENE BY T(3) AND T(3) RECEPTOR IN CV1 CELLS

We report that the activity of the firefly luciferase (LUC) reporter g ene is down-regulated by T3 and T3 receptor (TR) in the CV1 mammalian cell line, which is widely used for studies of TR action. Repression w as highly reproducible, T3 and TR dependent, promoter independent, and observed regardless of whether an internal control for transfection e fficiency was used. Cotransfections with normal and mutant TRs indicat e that the negative T3 response is mediated by sequences within the LU C gene coding region, and is not due to the interaction of TR with a l imiting transcription factor. Negative regulation of the LUC reporter was overcome by a strong, cis-linked T3 response element (TRE), but co ntinued in the presence of a TRE of moderate strength. The results des cribed here demonstrate that conclusions drawn from studies of TRE str ucture and activity performed using the LUC reporter in CV1 cells shou ld be interpreted with caution.