The mechanism for glucocorticoid-resistance in a rat hepatoma cell variant that contains functional glucocorticoid receptor

Sam Okret, Yu Dong, Hirotoshi Tanaka, Bill Cairns, Jan Åke Gustafsson

Research output: Contribution to journalArticlepeer-review

27 Scopus citations

Abstract

The mechanism of glucocorticoid resistance has been studied in a rat hepatoma cell variant (6.10.2),which contains low levels of glucocorticoid receptor (GR). These cells seem to have lost all the glucocorticoid-induced transcriptional responses as measured by the lack of induction of expression of stably integrated mouse mammary tumor virus (MMTV) and the endogenous gene tyrosine aminotransferase (TAT), as well as the transcriptional suppression of GR gene expression. Physico-chemical characterization of the GR in the glucocorticoid resistant 6.10.2 cells revealed that the receptor is indistinguishable from the wild-type receptor with regard to size hormone- and DNA-binding. The levels of the receptor mRNA and the total immunoreactive protein found in 6.10.2 cells were about 20% of those found in wild-type cells. Further analysis of 6.10.2 cells demonstrated that the receptor was indeed biologically functional. Treatment of 6.10.2 cells with 8-bromo-cAMP, which induced the endogenous GR level two-fold, restored responsiveness to glucocorticoids. Secondly, pretreatment of the cells with cycloheximide also led to reacquisition of cellular responsiveness to glucocorticoids. We propose that there exists a "threshold" level of GR, which is required for responsiveness and that under normal culture conditions, the level of GR in 6.10.2 cells is below this threshold. Glucocorticoid responsiveness can be restored by raising the GR level above the threshold with 8-bromo-cAMP or, alternatively, by removing the threshold barrier (repressor protein) with cycloheximide. Finally, the existence of such a repressor protein for MMTV induction was shown by in vivo titration with an isolated negative cis-element from the MMTV promoter.

Original languageEnglish (US)
Pages (from-to)353-361
Number of pages9
JournalJournal of Steroid Biochemistry and Molecular Biology
Volume40
Issue number1-3
DOIs
StatePublished - 1991

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Biochemistry
  • Molecular Medicine
  • Molecular Biology
  • Endocrinology
  • Clinical Biochemistry
  • Cell Biology

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