Variants of HTC cells with low tyrosine aminotransferinase inducibility and apparently normal glucorticoid receptors.

Variants of HTC cells showing little or no induction of tyrosine aminotransferase in response to glucorticoids have been isolated by repeated cloning without deliberate selective pressures. In this paper, the derivation and some properties of these cells, compared with both high-inducing clones and wild-type cells, are described. The non-inducing cells all grew well, and were not induced even by unusually high concentrations of steroid. The enzyme activity had a normal half-life of decay and heat inactivation. It was inactivated by antiserum against authentic tyrosine aminotransferase, and no evidence for antigenically active, enzymatically inactive enzyme was found. No great variability was seen in the few other enzyme activities tested. Glucorticoid receptors were present in all the clones, With respect to concentration, cellular uptake, cell-free binding to nuclei and intracellular localiztion, no differences were found between the receptors of inducible and non-inducible clones. These are the first cells derived from an inducible type to be characterized as having normal receptor while becoming steroid resistant. They appear to be blocked in a late step of the response to the steroid, and therefore may prove useful in analyzing these later steps.