Establishment of 8-azaguanine-resistant mutants from rat thyroid cell line FRTL-5.

8-Azaguanine (AG)-resistant mutant clones were isolated from FRTL-5 rat thyroid cells, by treating them with ethylmethane sulfonate for 48 h and then, after the recovery period, by selecting them in AG-containing medium. Isolated mutants were further selected in 6-thioguanine-containing medium, and two mutant clones were finally obtained (AG1 and AG2). The mutants retained several thyroid stimulating hormone (TSH) responsiveneses following acquisition of AG resistance: they responded to bovine TSH (bTSH), by producing cyclic 3',5'-adenosine monophosphate (cAMP) and thyroglobulin, and taking up iodine. However, TSH-responsive profiles were slightly different from each other in several points. They were killed in hypoxanthine-aminopterin-thymidine (HAT)-selective medium and applied to cell hybridization study with human thyrocyte from a Graves' patient: the hybrid turned out to produce both rat and human thyroglobulin even 12 months after the hybridization.