Characterization of dominant hamster cell mutants resistant to oxygenated sterols

Stable mutants of Dede and CHO cells, resistant to suppression of cholesterogenesis by oxygenated sterols, have been isolated in a single step. Luria-Delbrück fluctuation analysis indicated a random occurrence of resistant at a rate of 1 x 10(-7) mutations/cell/generation. Cholesterol biosynthesis, 3-hydroxy-3-methylglutaryl coenzyme A reductase activity, and growth of the mutant cells were coordinately resistant to oxygenated sterols in the culture medium, and this resistance was expressed as a dominant trait in somatic cell hybrids of the wild-type and mutant cells. The dominant resistance was employed in the selection of various cells hybrids. There was complete additivity of reductase activities in mixed lysates of inhibited wild-type and uninhibited mutant cells, indicating that cytosolic (in)activation factors were not causative of this resistance. We suggest that oxygenated sterols are (co)repressors in suppression of the synthesis of the reductase and that the resistance mutant phenotypes result from altered regulatory loci.