Characterization of selective glucocorticoid-dependent responses in a glucocorticoid-resistant smooth muscle tumor cell line

The DDT₁ MF2 smooth muscle cell line was derived from an estrogen/androgeninduced leiomyosarcoma arising in the hamster ductus deferens. Growth of this cell line is arrested in Go/G1 by treatment with glucocorticoids. To facilitate the study of the mechanism of glucocorticoid-induced cell growth arrest, a glucocorticoid-resistant variant cell line, DDT₁ MF2 GR1 (GR1), was developed by genetic selection. Growth of this mutant cell line is completely resistant to the inhibitory action of glucocorticoids. However, we now demonstrate that both primary and secondary glucocorticoid-induced events still exist in the GR1 cell line. By analyzing the expression and genetic pattern of glucocorticoid receptor, no detectable rearrangement of the glucocorticoid receptor gene was found although the expression of both mRNA and protein levels of the receptor were lower in the variant compared to wild-type cells. In addition, we found that the expression of two growth-associated genes, Ha-ras and transforming growth factor β1 (TGF-β1) are down-regulated by glucocorticoids in wild-type DDT₁ MF2 cells but not in GR1 cells. These results indicated that the function or activity of glucocorticoid receptor in the GR1 cells is not qualitatively altered. Our data suggest that a lower glucocorticoid receptor level is not the real cause or at least not the single cause for the GR1 cell's loss of sensitivity to the inhibitory action of glucocorticoid. Instead, we postulate the existence of a defect downstream of the primary site of action of glucocorticoid receptor complexes in GR1 cells. © 1993 Wiley-Liss, Inc.