The DDT1 MF2 smooth muscle cell line was derived from an
estrogen/
androgen-induced
leiomyosarcoma arising in the hamster ductus deferens. Growth of this cell line is arrested in G0/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 beta 1 (TGF-beta 1) 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.