DNA-dependent protein kinase (DNA-PK) permits vascular smooth muscle cell proliferation through phosphorylation of the orphan nuclear receptor NOR1.
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Medunjanin S, Daniel JM, Weinert S, Dutzmann J, Burgbacher F, Brecht S, Bruemmer D, Kahne T, Naumann M, Sedding DG, Zuschratter W, Braun-Dullaeus RC
DNA-dependent protein kinase (DNA-PK) permits vascular smooth muscle cell proliferation through phosphorylation of the orphan nuclear receptor NOR1.
Cardiovasc Res. 2015 Jun 1;106(3):488-97. doi: 10.1093/cvr/cvv126. Epub 2015 Apr 7.
- PubMed ID
- 25852083 [ View in PubMed]
- Abstract
AIMS: Being central part of the DNA repair machinery, DNA-dependent protein kinase (DNA-PK) seems to be involved in other signalling processes, as well. NOR1 is a member of the NR4A subfamily of nuclear receptors, which plays a central role in vascular smooth muscle cell (SMC) proliferation and in vascular proliferative processes. We determined putative phosphorylation sites of NDA-PK in NOR1 and hypothesized that the enzyme is able to modulate NOR1 signalling and, this way, proliferation of SMC. METHODS AND RESULTS: Cultured human aortic SMC were treated with the specific DNA-PK inhibitor NU7026 (or siRNA), which resulted in a 70% inhibition of FCS-induced proliferation as measured by BrdU incorporation. Furthermore, FCS-stimulated up-regulation of NOR1 protein as well as the cell-cycle promoting proteins proliferating cell nuclear antigen (PCNA), cyclin D1, and hyperphosphorylation of the retinoblastoma protein were prevented by DNA-PK inhibition. Co-immunoprecipitation studies from VSM cell lysates demonstrated that DNA-PK forms a complex with NOR1. Mutational analysis and kinase assays demonstrated that NOR1 is a substrate of DNA-PK and is phosphorylated in the N-terminal domain. Phosphorylation resulted in post-transcriptional stabilization of the protein through prevention of its ubiquitination. Active DNA-PK and NOR1 were found predominantly expressed within the neointima of human atherosclerotic tissue specimens. In mice, inhibition of DNA-PK significantly attenuated neointimal lesion size 3 weeks after wire-injury. CONCLUSION: DNA-PK directly phosphorylates NOR-1 and, this way, modulates SMC proliferation. These data add to our understanding of vascular remodelling processes and opens new avenues for treatment of vascular proliferative diseases.