Cyclic Adenosine 3′,5′-Monophosphate Regulation of Corticotropin-Releasing Hormone Promoter Activity in AtT-20 Cells and in a Transformed Hypothalamic Cell Line

• Published in: Endocrinology (Philadelphia) Vol. 144; no. 4; pp. 1292 - 1300
• Main Authors: Nikodemova, Maria, Kasckow, John, Liu, Hanguan, Manganiello, Vincent, Aguilera, Greti
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Endocrine Society 01.04.2003
• Subjects: 1-Methyl-3-isobutylxanthine - pharmacology; 8-Bromo Cyclic Adenosine Monophosphate - pharmacology; Animals; Biological and medical sciences; Cell Line; Cell Line, Transformed; Colforsin - pharmacology; Corticotropin-Releasing Hormone - genetics; Cyclic AMP - metabolism; Cyclic AMP-Dependent Protein Kinases - metabolism; Fundamental and applied biological sciences. Psychology; Gene Expression - drug effects; Gene Expression - physiology; Hypothalamus - cytology; Phosphodiesterase Inhibitors - pharmacology; Phosphoric Diester Hydrolases - metabolism; Pituitary Gland - cytology; Promoter Regions, Genetic - physiology; Rats; Vasopressins - genetics
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/en.2002-220990

The regulation of CRH promoter activity by cAMP was studied in two cell lines, the pituitary corticotroph cell line AtT-20 and the immortalized hypothalamic cell line 4B, which expresses CRH and vasopressin. In 4B cells transfected with a CRH promoter-luciferase construct, the adenylyl cyclase stimulator, forskolin, increased luciferase activity in parallel with increases in intracellular cAMP. In 4B cells, however, the phosphodiesterase inhibitor, isobutylmethylxanthine, potentiated forskolin-stimulated cAMP without affecting further increases in luciferase activity. In AtT-20 cells, forskolin plus isobutylmethylxanthine elevated cAMP only slightly, but increased luciferase activity to levels similar to those observed in 4B cells. AtT-20 cells were also unresponsive to 8-bromo-cAMP, due in part to higher phosphodiesterase (PDE) activities. Although both cells contained PDE1, -3, and -4, inhibition of either PDE4 or PDE1 potentiated luciferase activity stimulated by submaximal forskolin concentrations in 4B cells, while only simultaneous inhibition of PDE3 and PDE4 was effective in AtT-20 cells. The data show that minor elevations in intracellular cAMP are sufficient for full stimulation of CRH promoter activity regardless of the cell line. Furthermore, poor CRH promoter activation in AtT-20 cells appears to result from deficient cAMP production and rapid cAMP degradation by PDE.