Cyclic adenosine 3',5'-monophosphate regulation of corticotropin-releasing hormone promoter activity in AtT-20 cells and in a transformed hypothalamic cell line.
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.
Nikodemova
Maria
M
Section on Endocrine Physiology, Developmental Endocrinology Branch, National Institutes of Health, Bethesda, Maryland 20892, USA.
Kasckow
John
J
Liu
Hanguan
H
Manganiello
Vincent
V
Aguilera
Greti
G
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D002461:Cell Line, Transformed; D005576:Colforsin / Q000494:pharmacology; D003346:Corticotropin-Releasing Hormone / Q000235:genetics*; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects / Q000502:physiology; D007031:Hypothalamus / Q000166:cytology*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D010902:Pituitary Gland / Q000166:cytology; D011401:Promoter Regions, Genetic / Q000502:physiology*; D051381:Rats; D014667:Vasopressins / Q000235:genetics
D010726:Phosphodiesterase Inhibitors; D014667:Vasopressins; D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D003346:Corticotropin-Releasing Hormone; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D010727:Phosphoric Diester Hydrolases; D015056:1-Methyl-3-isobutylxanthine