Glucocorticoid Receptor Structure and Function in an Adrenocorticotropin-Secreting Small Cell Lung Cancer

Mol Endocrinol. 1995 Sep;9(9):1193-201. doi: 10.1210/mend.9.9.7491111.

Abstract

ACTH secretion by tumors of nonpituitary origin is characteristically resistant to negative feedback regulation by glucocorticoids. One possible mechanism for the phenomenon could be a structural defect in the intracellular glucocorticoid receptor (GR). We studied the GR in DMS-79 cells derived from a human ACTH-secreting small cell lung cancer. Compared with control cells, DMS-79 cells were found to have greatly diminished GR ligand-binding activity and immunoreactive 94-kilodalton (kDa) GR content. Northern blot analysis revealed expression of GR transcripts that appeared to be slightly larger than those in control cells. A DMS-79 cell GR cDNA was cloned by reverse transcription/polymerase chain reaction amplification of mRNA using primers specific for full-length normal GR. The derived sequence of this full-length GR differed from the reported sequence by a single altered codon (G to A; Asn to Ser at codon 363) outside the steroid-binding domain. This N363S DMS-79 GR functioned normally to activate a target gene [mouse mammary tumor virus-chloramphenicol acetyl transferase (MMTV-CAT)] in transient transfection experiments in COS cells. Evidence for expression of a second type of GR mRNA was obtained by screening a DMS-79 cell cDNA library. This GR cDNA contained normal GR sequence up to nucleotide 2155, corresponding exactly to the end of exon 7 in the normal GR gene. The sequence appended to the GR sequences was not matched by any known sequence in DNA databases and included an in-frame termination codon after only 6 bases. The predicted truncated GR protein product (GR delta) has a mol wt of 73,740 and lacks most of the ligand-binding domain. Transient transfection of the GR delta form into COS cells did not reveal any dominant negative effect on the function of a cotransfected normal GR.(ABSTRACT TRUNCATED AT 250 WORDS)

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adrenocorticotropic Hormone / metabolism*
  • Animals
  • Base Sequence
  • Blotting, Northern
  • Carcinoma, Small Cell / metabolism*
  • DNA, Complementary / chemistry
  • Humans
  • Lung Neoplasms / metabolism*
  • Mice
  • Molecular Sequence Data
  • RNA, Messenger / analysis
  • Receptors, Glucocorticoid / chemistry*
  • Receptors, Glucocorticoid / genetics
  • Receptors, Glucocorticoid / physiology*
  • Signal Transduction
  • Transfection
  • Tumor Cells, Cultured

Substances

  • DNA, Complementary
  • RNA, Messenger
  • Receptors, Glucocorticoid
  • Adrenocorticotropic Hormone

Associated data

  • GENBANK/U25029