Abstract 13896: The Bromodomain-containing Protein 4: the Epigenetic Origin of the Cancer Paradigm in Pulmonary Arterial Hypertension
Background: As in cancer, pulmonary arterial hypertension (PAH) is associated with sustained DNA damage accounting for a PARP-1-dependent downregulation of miR-204. By an unknown mechanism, miR-204 downregulation promotes the expression of oncogenes implicated in PAH including Survivin, Bcl-2, Pim-1 and c-Myc. Once activated, by affecting the mitochondrial function through the transcription factor NFAT, they contribute to the pro-proliferative and anti-apoptotic phenotype of PAH-pulmonary arterial smooth muscle cells (PAH-PASMC). In cancer, the increase of the epigenetic reader Bromodomain-containing protein 4 (BRD4) increases the transcription of multiple oncogenes sustaining cell proliferation. Interestingly, BRD4 is upregulated by DNA damage and is a predicted target of miR-204. We hypothesized that the PARP-1/miR-204-dependent upregulation of BRD4 triggers the oncogenes-dependent pro-proliferative and anti-apoptotic phenotype seen in PAH-PASMC.
Method/Results: BRD4 is upregulated (immunoblot; p<0.01) in the lungs, distal PAs and PASMC of PAH patients (n=5) compared to control (n=5). This increase is miR-204 dependent, as miR-204 (downregulated in PAH) upregulation using mimic in PAH-PASMC decreases BRD4 (p<0.05). Compared to control PASMC, BRD4 activation in PAH-PASMC induces Survivin, c-Myc and Pim-1 expression (immunoblot; p<0.05), leading to mitochondrial hyperpolarization (TMRM; p<0.05), decreasing mitochondrial respiration (Seahorse XFe 24) and increasing NFAT activation (p<0.05), all of which were reversed upon molecular (siRNA) and pharmacological ((+)JQ1 and I-BET762) inhibition of BRD4. Finally, BRD4 inhibition reverses PAH-PASMC proliferation (Ki67; p<0.05) and resistance to apoptosis (TUNEL; p<0.05).
Conclusion: Through a miR-204-dependent mechanism, BRD4 upregulation triggers the expression of multiple oncogenes contributing to the proliferative and anti-apoptotic phenotype seen in PAH-PASMC, whereas BRD4 inhibition improves PAH. As BRD4 inhibitors have recently been developed and tested in cancer, this offers a short-term new therapeutic perspective for PAH patients.
Author Disclosures: M. Vaillancourt: None. J. Meloche: None. P. Ferraro: None. S. Provencher: None. S. Bonnet: Research Grant; Modest; Bayer. Other Research Support; Modest; actellion. Honoraria; Modest; Merck.
- © 2014 by American Heart Association, Inc.