Dexamethasone regulates somatostatin receptor subtype messenger ribonucleic acid expression in rat pituitary GH4C1 cells

Ligand binding studies have shown that glucocorticoids down-regulate somatostatin receptor (sst) concentration in several endocrine target cells and cell lines including GH4C1 cells. However, it has not been determined whether this decrease in sst number occurred via transcriptional and/or posttranscriptional events. In the present study, we have investigated the effect of dexamethasone (Dex) treatment (1 microM) of GH4C1 cells for up to 48 h on the steady state level of messenger RNA (mRNA) for sst1, sst2, and sst3, the predominant isoforms expressed in this cell line, by solution hybridization-nuclease protection analysis. Exposure of GH4C1 cells to Dex for 2 h increased sst1 mRNA levels 2.5-fold and sst2 1.5-fold compared with controls (Con). Prolonged exposure, however, resulted in a decrease in mRNA levels of sst1 to 50% and sst2 to 30% of Con by 24-48 h. In contrast, sst3 mRNA levels were unchanged at 2 h, decreased to 30% of Con by 6 h, and remained decreased for up to 24 h. Longer exposure resulte...