Characteristics of a thyroid hormone responsive reporter gene transduced into a Xenopus laevis cell line using lentivirus vector

We introduced a self-inactivation (SIN) lentivirus vector (LV) into Xenopus laevis cell lines and established a permanent cell line expressing a reporter gene in a 3,5,3′-l-triiodothyronine (T3) dependent manner. The SIN LV contained the luciferase gene downstream from the X. laevis T3-response elements (TREs) and the SV40 promoter, and the enhanced green fluorescent protein (EGFP) gene downstream from the cytomegalovirus (CMV) promoter. It was integrated into the genome of X. laevis XL58, XTC2, and KR cells. The SIN LV transduced the X. laevis cells as efficiently as mammalian cells; however, the expression of EGFP in the transgene decreased with increasing culture time. A cell clone exhibiting the highest TH-dependent luciferase gene expression (XL58-TRE-Luc clone) was isolated from the EGFP-positive XL58 cell pool and characterized. The minimum effective concentration of T3 that significantly induced the luciferase gene expression was 10−11 M in the XL58-TRE-Luc clone. The application of the luciferase gene assay using the permanent XL58-TRE-Luc clone for the screening of thyroid-disrupting chemicals revealed that tetrachlorobisphenol A, at 10−6 M, had a weak T3-agonist activity, whereas trichlorobisphenol A, at 10−8-10−6 M had a weak T3-antagonist activity. Our results indicated that the permanent X. laevis cell line containing a T3-response transgene could be used as a bioassay, with small intra-assay variation, for the rapid screening, identification, and characterization of the thyroid-disrupting chemicals.