Half-life of aryl hydrocarbon receptor in Hepa 1 cells: evidence for ligand-dependent alterations in cytosolic receptor levels

Arch Biochem Biophys. 1993 Apr;302(1):167-74. doi: 10.1006/abbi.1993.1195.

Abstract

The rate of turnover of the Ah receptor (AhR) was determined using the density shift method in Hepa 1 and in a Hepa 1 mutant line, c4, which fails to accumulate AhR complexes in the nucleus. The half-life of the AhR was found to be 7.7 and 9.7 h in Hepa 1 and c4 cells, respectively. The effect of AhR occupation with either an agonist, beta-naphthoflavone (beta NF), or a partial antagonist, alpha-naphthoflavone (alpha NF), on AhR half-life and concentration in the cytosolic fraction was examined. In Hepa 1 cells, a 12-h exposure to beta NF resulted in a 62% decrease in AhR concentration. The same treatment, using alpha NF as the ligand, resulted in a 14% decrease. The half-life of the AhR increased from 7.7 to 9.3 h during beta NF treatment and was essentially the same during alpha NF treatment in Hepa 1 cells. In c4 cells, a 12-h exposure to beta NF resulted in a 44% decrease in AhR concentrations, whereas exposure to alpha NF resulted in an 8% decrease. The half-life of the AhR in c4 cells during beta NF exposure increased from 9.7 to 14.6 h, and alpha NF exposure increased half-life to 17.6 h. These results indicate: (a) cytosolic AhR concentrations are modulated by ligand occupation, (b) exposure to AhR ligands, after an initial decrease in AhR levels, resulted in an increase in AhR half-life, and (c) similar results were obtained in Hepa 1 and c4 cells, this would indicate that AhR occupation with ligand and subsequent AhR-ligand nuclear translocation does not appear to play a significant role in regulation of AhR half-life in Hepa 1 cells.

Publication types

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

MeSH terms

  • Animals
  • Benzoflavones / pharmacology
  • Cell Nucleus / metabolism
  • Cytosol / metabolism
  • Half-Life
  • Ligands
  • Liver Neoplasms, Experimental / metabolism*
  • Mice
  • Receptors, Aryl Hydrocarbon
  • Receptors, Drug / metabolism*
  • Tumor Cells, Cultured
  • beta-Naphthoflavone

Substances

  • Benzoflavones
  • Ligands
  • Receptors, Aryl Hydrocarbon
  • Receptors, Drug
  • alpha-naphthoflavone
  • beta-Naphthoflavone