Why the study?
The mechanisms by which TPA inhibits angiotensin II-stimulated CYP11B2 gene expression in adrenocortical cells were not fully understood.
The study demonstrates that TPA inhibits angiotensin II-stimulated aldosterone synthase expression in adrenocortical cells through the p44/42 MAPK signaling pathway and increased nuclear JunB.
May warrant aldosterone monitoring during MEK inhibitor use; leaves open ERK pathway role in clinical hyperaldosteronism.
We have previously reported that the protein kinase C ligand 12-O-tetradecanoyphorbol-13-acetate (TPA) inhibited the angiotensin II (AII) stimulated CYP11B2 gene expression in the adrenocortical H295R cell line. Here we report that TPA increased the level of phospho-p44/42 MAPK but AII did not. The MEK1 inhibitor PD98059 was found to increase the level of aldosterone synthase mRNA and the activity of a human CYP11B2(-2023 bp)-promoter construct. The cotransfection of H295R with ERK 1 and the hCYP11B2 promoter resulted in the inhibition of the promoter activity. TPA but not AII increased the level of the transcription factor JunB in nuclear extracts and the increase was partially abolished by the MEK1 inhibitor PD98059. The cotransfection of H295R with JunB and the hCYP11B2 promoter abolished the AII stimulating effect. Taken together these results suggest that TPA inhibits the AII-dependent activation of CYP11B2 via the p44/42 MAPK signaling pathway leading to an increase of the level of nuclear JunB.
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Lehoux et al. (2004) studied this question. 12-O-tetradecanoyphorbol-13-acetate (TPA) vs. Angiotensin II alone was evaluated on CYP11B2 gene expression and promoter activity.
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