Synergistic enhancement of PRB-mediated RU486 and R5020 agonist activities through cyclic adenosine 3',5'-monophosphate represents a delayed primary response.
Activators of protein kinase A have been shown to affect the transactivation potential of progestins and antiprogestins. To analyze the mechanisms and factors involved, we have created HeLa and CV1 cell clones stably expressing isoform B of progesterone receptor. In the HeLa cell background, the progesterone antagonist RU486 significantly induces progesterone-regulatable reporter genes, and this agonistic effect is synergistically enhanced by elevating cAMP or through overexpression of protein kinase A catalytic subunit. In contrast, in CV1 cells containing functional progesterone receptors no agonist activity of RU486 could be detected, suggesting the involvement of cell specifically expressed factors. In a PR(B)-positive HeLa cell clone containing stably integrated copies of a thymidine kinase-luciferase reporter gene with two progesterone response elements, we observed a complete loss of RU486 antagonist potential upon cotreatment with cAMP for 25 h while partial antagonist potential was maintained in a 5-h experiment. This result shows that, particularly in the presence of protein kinase A activators, the duration of hormone treatment is a crucial parameter in the evaluation of antagonist properties of antiprogestins. A detailed analysis of the kinetics of the hormone effects on transcription revealed that the onset of cAMP/RU486 synergism is delayed relative to the responses induced by RU486 or R5020 alone. Moreover, partial inhibition of protein synthesis by cycloheximide completely abolished cAMP/RU486 synergism while R5020 and RU486 responses were not inhibited. Together, these data indicate that cAMP/RU486 synergism is a delayed primary response requiring the intermediate induction of an essential factor.
Kahmann
S
S
Institut für Zellbiologie (Tumorforschung) Universitätsklinikum, Essen, Germany.
Vassen
L
L
Klein-Hitpass
L
L
D002875:Chromosomes / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism / Q000494:pharmacology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D004357:Drug Synergism; D005260:Female; D017930:Genes, Reporter; D006367:HeLa Cells; D006801:Humans; D008324:Mammary Tumor Virus, Mouse / Q000235:genetics; D015735:Mifepristone / Q000819:agonists / Q000494:pharmacology*; D011397:Promegestone / Q000819:agonists / Q000494:pharmacology*; D011980:Receptors, Progesterone / Q000819:agonists / Q000096:biosynthesis / Q000502:physiology*; D013347:Subcellular Fractions / Q000378:metabolism
D011980:Receptors, Progesterone; C097314:progesterone receptor B; D015735:Mifepristone; D011397:Promegestone; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases