Isolation and characterization of HPRT-deficient human hepatoma cells.

Human hepatoma cells deficient in HPRT activity were isolated by challenging HepG2 cells with 6-thioguanine (6TG). Three 6TG-resistant isolates were plated in selective media, and each clonal line displayed an 8-azaguanine-resistant, HAT-sensitive phenotype. The HPRT-deficient phenotype of one of these clones, H30-1, was confirmed in genetic tests: the HAT-sensitivity of H30-1 cells was complemented by fusion by HPRT+ (Ltk-) but not HPRT- (A9) cells. Furthermore, transfection of the bacterial xanthine-guanine phosphoribosyl transferase (gpt) gene into H30-1 cells rendered them HAT-resistant. H30-1 cells maintained the differentiated morphology, growth characteristics, fusion properties, and transfection efficiencies typical of parental HepG2 cells, and they expressed several liver-specific genes. Finally, the H30-1 cell line contained a modal number of 50 chromosomes. Therefore, H30-1 cells represent an HPRT-deficient HepG2 derivative that retains its differentiated phenotype in vitro.