Bidirectional regulation of the 1, 25-dihydroxyvitamin d3receptor by phorbol ester-activated protein kinase-c in osteoblast-like cells: Interaction with adenosine 3’, 5’-monophosphate-induced up-regulation of the 1, 25-dihydroxy vitamin d3receptor

J. P.T.M.Van Leeuwen*, J. C. Birkenhäger, C. J. Buurman, G. J.C.M.Van Den Bemd, M. P. Bos, H. A.P. Pols

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

33 Citations (Scopus)

Abstract

In the present study the involvement of protein kinase-C (PKC) in the regulation of the vitamin D receptor (VDR) and interaction of PKC with cAMP-induced up-regulation of VDR in osteoblast-like cells were examined. Activation of PKC by incubation for 4 h with the phorbol ester phorbol 12-myristate 13-acetate (PMA) resulted in a comparable dose-dependent decrease in 1, 25-dihydroxyvitamin D3binding in the osteoblast-like cell lines UMR 106 and ROS 17/2.8, with a maximum inhibition at 100 nM and an IC50at 5 nM PMA. Time-course studies revealed that in both UMR 106 and ROS 17/2.8 cells, 24-h incubation with PMA caused an increase in 1, 25-dihydroxyvitamin D3binding. This can be related to down-regulation of PKC. Scatchard analysis demonstrated that activation of PKC resulted not in a change in receptor affinity, but, rather, in an increase in VDR number. This is supported by Northern blot analysis, which shows at 2 h a decrease and at 24 h an increase in VDR mRNA. At 4 h, when activation of the cAMP pathway results in an increase in VDR, activation of PKC results in a decrease in VDR. Coincubation for 4 h with PMA caused a decrease in PTH- and forskolin-induced up-regulation of VDR. This inhibition is not due to a reduction in cAMP production, as PTH-stimulated cAMP production was potentiated by PMA. The effect of activation of PKC on VDR is not a general effect, as PMA does not affect basal ornithine decarboxylase activity and potentiates PTH-induced ornithine decarboxylase activity. The present study demonstrates that PKC is involved in the regulation of VDR in UMR 106 and ROS 17/2.8 and that PKC interacts with cAMP in the regulation of VDR. The current data point to a negative controlling role for PKC in the regulation of VDR. Moreover, two different cAMPregulated actions in UMR 106 cells (VDR up-regulation and ornithine decarboxylase activity) are differently modulated by PKC. Although the precise mechanism by which PKC represses and stimulates gene expression is not yet clear, this study demonstrates the important regulatory role for PKC in two osteoblast-like sarcoma cell lines.

Original languageEnglish
Pages (from-to)2259-2266
Number of pages8
JournalEndocrinology
Volume130
Issue number4
DOIs
Publication statusPublished - Apr 1992

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