Cloning of a μ-class glutathione S-transferase complementary DNA and characterization of its glucocorticoid inducibility in a smooth muscle tumor cell line

A cDNA (designated hGSTYBX) encompassing the complete coding sequence of a hamster μ-class glutathione S-transferase (GST) subunit was cloned from a λZAP library constructed with mRNA isolated from triamcinolone acetonide-treated smooth muscle tumor cells (DDT₁ MF-2). Analysis of its nucleotide and deduced amino acid sequences demonstrated highest homology to the rat μ-class GST YB2 subunit. In proliferating subconfluent cells, in which constitutive expression of hGSTYBX mRNA was undetectable, glucocorticoid treatment induced hGSTYBX expression after a time lag of 3 h, and maximal induction occurred at 10 h. Nuclear run-on analysis showed that glucocorticoid induction resulted at least in part from an increased rate of transcription. Simultaneous treatment with glucocorticoid and cycloheximide prevented glucocorticoid induction, but had little effect on basal expression in confluent cells. In contrast, cycloheximide treatment 3 h after glucocorticoid treatment resulted in nearly full induction. These results taken together suggest that hGSTYBX induction may be a second-ary glucocorticoid response.