Table 1.

Relative ability of different TG preparations to decrease TPO gene expression in FRTL-5 thyroid cells

TG source and characteristics	Relative inhibition activity
Bovine TG
Sigma	1
Salt-extracted/agarose-purified 19S	6.8  ±  3
Human TG–salt-extracted/agarose-purified 19S
Normal thyroid	8.5  ±  2
Iodide deficiency goiter	15  ±  3*
Colloid adenoma	18  ±  3*

Bold and italicized values represent significantly improved inhibition relative to the action of Sigma TG (P < 0.01); asterisks indicate values that are significantly higher than TG from normal human thyroids (P < 0.05). FRTL-5 cells in 6H medium containing 5% calf serum were transfected with 5 μg of the TPO-luciferase chimera, pTPO-1372-LUC, by using a DEAE procedure. Cells were washed with 6H medium without serum, and the different types of TG were added; luciferase activity was measured 48 h later. The activity of 1 mg/ml of each of the TG preparations was compared; the activity of 1 mg/ml Sigma TG was the arbitrary standard having 1 unit of activity. The same data were obtained with two other TPO-luciferase chimeras (pTRO-6300-LUC; pTRO-181-LUC) and were not duplicated by albumin.