Differential Regulation of Telomerase Reverse Transcriptase Promoter Activation and Protein Degradation by Histone Deacetylase Inhibition.

Telomerase reverse transcriptase (TERT) maintains telomeres and is rate limiting for replicative life span. While most somatic tissues silence TERT transcription resulting in telomere shortening, cells derived from cancer or cardiovascular diseases express TERT and activate telomerase. In the present study, we demonstrate that histone deacetylase (HDAC) inhibition induces TERT transcription and promoter activation. At the protein level in contrast, HDAC inhibition decreases TERT protein abundance through enhanced degradation, which decreases telomerase activity and induces senescence. Finally, we demonstrate that HDAC inhibition decreases TERT expression during vascular remodeling in vivo. These data illustrate a differential regulation of TERT transcription and protein stability by HDAC inhibition and suggest that TERT may constitute an important target for the anti-proliferative efficacy of HDAC inhibitors.

Qing H ，Aono J ，Findeisen HM ，Jones KL ，Heywood EB ，Bruemmer D ... -  《-》

Epigenetic regulation of vascular smooth muscle cell proliferation and neointima formation by histone deacetylase inhibition.

Findeisen HM ，Gizard F ，Zhao Y ，Qing H ，Heywood EB ，Jones KL ，Cohn D ，Bruemmer D ... -  《-》

Telomerase Reverse Transcriptase Deficiency Prevents Neointima Formation Through Chromatin Silencing of E2F1 Target Genes.

Aberrant proliferation of smooth muscle cells (SMC) in response to injury induces pathological vascular remodeling during atherosclerosis and neointima formation. Telomerase is rate limiting for tissue renewal and cell replication; however, the physiological role of telomerase in vascular diseases remains to be determined. The goal of the present study was to determine whether telomerase reverse transcriptase (TERT) affects proliferative vascular remodeling and to define the molecular mechanism by which TERT supports SMC proliferation. We first demonstrate high levels of TERT expression in replicating SMC of atherosclerotic and neointimal lesions. Using a model of guidewire-induced arterial injury, we demonstrate decreased neointima formation in TERT-deficient mice. Studies in SMC isolated from TERT-deficient and TERT overexpressing mice with normal telomere length established that TERT is necessary and sufficient for cell proliferation. TERT deficiency did not induce a senescent phenotype but resulted in G1 arrest albeit hyperphosphorylation of the retinoblastoma protein. This proliferative arrest was associated with stable silencing of the E2F1-dependent S-phase gene expression program and not reversed by ectopic overexpression of E2F1. Finally, chromatin immunoprecipitation and accessibility assays revealed that TERT is recruited to E2F1 target sites and promotes chromatin accessibility for E2F1 by facilitating the acquisition of permissive histone modifications. These data indicate a previously unrecognized role for TERT in neointima formation through epigenetic regulation of proliferative gene expression in SMC.

Endorf EB ，Qing H ，Aono J ，Terami N ，Doyon G ，Hyzny E ，Jones KL ，Findeisen HM ，Bruemmer D ... -  《-》

Drugs targeting epigenetic histone acetylation in vascular smooth muscle cells for restenosis and atherosclerosis.

Natarajan R 《-》

DNA-dependent protein kinase (DNA-PK) permits vascular smooth muscle cell proliferation through phosphorylation of the orphan nuclear receptor NOR1.

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. 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. 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.

Medunjanin S ，Daniel JM ，Weinert S ，Dutzmann J ，Burgbacher F ，Brecht S ，Bruemmer D ，Kähne T ，Naumann M ，Sedding DG ，Zuschratter W ，Braun-Dullaeus RC ... -  《-》