PIM1 (Moloney Murine Leukemia Provirus Integration Site) Inhibition Decreases the Nonhomologous End-Joining DNA Damage Repair Signaling Pathway in Pulmonary Hypertension

Abstract

Objective: Pulmonary arterial hypertension (PAH) is a fatal disease characterized by the narrowing of pulmonary arteries (PAs). It is now established that this phenotype is associated with enhanced PA smooth muscle cells (PASMCs) proliferation and suppressed apoptosis. This phenotype is sustained in part by the activation of several DNA repair pathways allowing PASMCs to survive despite the unfavorable environmental conditions. PIM1 (Moloney murine leukemia provirus integration site) is an oncoprotein upregulated in PAH and involved in many prosurvival pathways, including DNA repair. The objective of this study was to demonstrate the implication of PIM1 in the DNA damage response and the beneficial effect of its inhibition by pharmacological inhibitors in human PAH-PASMCs and in rat PAH models. Approach and Results: We found in vitro that PIM1 inhibition by either SGI-1776, TP-3654, siRNA (silencer RNA) decreased the phosphorylation of its newly identified direct target KU70 (lupus Ku autoantigen protein p70) resulting in the inhibition of double-strand break repair (Comet Assay) by the nonhomologous end-joining as well as reduction of PAH-PASMCs proliferation (Ki67-positive cells) and resistance to apoptosis (Annexin V positive cells) of PAH-PASMCs. In vivo, SGI-1776 and TP-3654 given 3× a week, improved significantly pulmonary hemodynamics (right heart catheterization) and vascular remodeling (Elastica van Gieson) in monocrotaline and Fawn-Hooded rat models of PAH. Conclusions: We demonstrated that PIM1 phosphorylates KU70 and initiates DNA repair signaling in PAH-PASMCs and that PIM1 inhibitors represent a therapeutic option for patients with PAH.

DNA Damage and Repair in Pulmonary Arterial Hypertension

“…Beyond DNA damage, various studies focused on the status of DDR in PAH have ascertained a dysfunctional repair mechanism leading to an augmented apoptosis-resistant and proliferative phenotype [ 49 , 67 , 73 , 88 ]. Taken together, it is likely that the pathways underlying DDR play a key role in PAH.…”

“…At present, there is not enough evidence to draw conclusions on the status of different DNA repair pathways in PAH. There are reports suggesting amplified DDR in PAH-PASMCs [ 49 , 67 ], while a few stand in contradiction ( Table 1 : OGG1, RAD51), reporting reduced DDR in PAH-PAECs [ 47 , 65 , 89 ] under different DNA damaging environments ( Table 1 ). One of the major reasons behind this gap is a lack of paired cell types from the patients in the same study, as well as replication of the findings across different types of PAH.…”

“…In another study from the same group, Lampron and colleagues explored the role of Moloney murine leukemia provirus integration site (PIM1) [ 67 ], a regulator of NHEJ repair pathway gene in PAH [ 68 ]. Increased PIM1 expression was observed in PAH lungs and PASMCs as compared to the controls [ 67 ]. PIM1 inhibition itself did not increase DNA damage; however, it reduced the expression of its downstream target, KU70, encoded by the gene X-Ray Repair Cross Complementing 6 ( XRCC6 ) that stabilizes the ends of DSBs.…”

“…Overall, PIM1 reduction significantly reduced the DNA repair capacity of the cells by inhibiting the primary events involved in DNA repair. Treatment with PIM1 inhibitors SGI-1776 and TP-3654 affected proliferation and apoptosis in PAH-PASMCs in an anti-pathological manner ( Figure 3 ) [ 67 ]. These observations were recapitulated in PH animal models, where pharmacological intervention in two experimental rat models with PIM1 inhibitors improved the hemodynamic characteristics, reduced vascular remodeling, reduced proliferation, and enhanced apoptosis [ 67 ].…”

“…Treatment with PIM1 inhibitors SGI-1776 and TP-3654 affected proliferation and apoptosis in PAH-PASMCs in an anti-pathological manner ( Figure 3 ) [ 67 ]. These observations were recapitulated in PH animal models, where pharmacological intervention in two experimental rat models with PIM1 inhibitors improved the hemodynamic characteristics, reduced vascular remodeling, reduced proliferation, and enhanced apoptosis [ 67 ]. As opposed to the previous pharmacological inhibitor of the DNA repair pathway studied by this group [ 66 ], PIM1 inhibition does not expose vascular cells to additional genetic insults.…”