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Biphasic Regulation of the Messenger Ribonucleic Acid Coding for the Estrogen Receptor by Cyclic Adenosine 3':5'-Monophosphate in Tumor Leydig Cells¹

Institute of Medical Biochemistry, University of Oslo, P. O. Box 1112 Blindern, 0317 Oslo3 [A. H. R., A. F., W. E., T. J., V. H.], and Laboratory of Gene Technology, Institute of Pathology, Rikshospitalet, Oslo [T. J.], Norway

In this report we show that the mRNA level for the estrogen receptor (ER) is regulated by 8-bromo cyclic AMP (8-Br-cAMP) and human chorionic gonadotropin in a mouse tumor Leydig cell line (MA-10 cells). When the MA-10 cells were cultured in the presence of the cAMP analogue for varying time periods, a transient increase in the level of ER mRNA was observed. Short time incubation (0–2 h) with 8-Br-cAMP enhanced the expression of ER mRNA (2-fold), whereas longer times of incubation (6 h) had the opposite effect (the level of ER mRNA was reduced by 60–70%). The inhibitory effect of 8-Br-cAMP on ER mRNA was not counteracted by aminoglutethimide, an inhibitor of steroidogenic enzymes, indicating that this effect is not mediated via steroids (progesterone). Treatment of 8-Br-cAMP for 6 h caused a concentration-dependent inhibition of ER mRNA with a half-maximal effect of approximately 150 µM.

Increasing concentrations of human chorionic gonadotropin for 6 h was also associated with a biphasic effect on the ER mRNA level. Low concentrations (0.20–0.40 ng/ml) increased ER mRNA in the MA-10 cells whereas the highest concentration (20 ng/ml) caused a suppression of this mRNA.

In contrast to the biphasic effects observed for the ER mRNA, the level of the regulatory subunit type II_ß of the cAMP-dependent protein kinase (protein kinase A) was enhanced in a concentration-dependent manner by human chorionic gonadotropin. Furthermore, 8-Br-cAMP stimulated the mRNA for regulatory subunit type II_ß (10- to 20-fold) by all concentrations examined (50–1000 µM).

The observations reported here indicate that the expression of ER mRNA is regulated both by endogenously formed and exogenously added cAMP and that there may exist regulatory loops between the steroid and the cAMP/protein kinase A systems.

¹ This work was supported by the Norwegian Research Council for Science and the Humanities, The Norwegian Cancer Society, The Nordic Insulin Foundation, and Jacob Aal's grant.

² To whom requests for reprints should be addressed.

Received 6/14/89. Revised 10/ 5/89. Accepted 12/ 4/89.

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