Originally named T-cell-originated Lymphokine-activated killer protein kinase (TOPK), PDZ-Binding Kinase (PBK) is a serine/threonine kinase that is a member of the family of mitogen-activated protein kinases (MAPKKs), which is overexpressed in lung cancer and interstitial pulmonary fibrosis (IPF). Along these lines, recent work also shows that PBK expression is upregulated in pulmonary arterial hypertension (PAH) in part due to the inappropriate proliferation of pulmonary arterial smooth muscle cells (PASMC), similar to the hyper-proliferative cellular properties seen in both lung cancer and IPF. Genetic knock-out of PBK as well as pharmacologically selective inhibitors of PBK improve PA remodeling and cardiopulmonary function. Further, PBK bound to the Protein Regulator of Cytokinesis 1 (PRC1) induces PRC1 phosphorylation and cytokinesis in PASMC, and thus, it is conjectured that PBK enhances PASMC proliferation via PRC1-mediated cytokinesis, identifying a key mechanism which contributes to the pathologic pulmonary vascular remodeling that occurs in PAH. Towards this end, along with the already published studies showing that PBK is involved in both lung cancer and IPF, PBK-mediated pulmonary vascular remodeling reveals a new signaling pathway in lung vascular disease and a novel mechanism of PASMC proliferation. Exploration of this signaling pathway will advance the utility of identifying novel therapeutic approaches targeting PBK-mediated cytokinesis to reduce pulmonary vascular remodeling (as seen in PAH) and subsequently improve the morbidity and mortality associated with lung vascular disease. Collectively, the literature strongly suggests that PBK is a worthy and viable therapeutic target to pursue in the context of lung disease.

OBJECTIVE:This study utilized AAV gene delivery as an approach to induce and reverse hyperphagia in mice. We hypothesized that the delivery of orexigenic neuropeptides to the brain via AAV precipitates obesity and that the implementation of genetic switches to reverse transgene expression would elicit weight loss. METHODS:We utilized capsid-modified AAV-PHP.eB and AAV-CAP.B10 to deliver AgRP, NPY, a leptin superantagonist, and ghrelin to the mouse brain. Cre-LoxP, TETOFF, and cumate expression systems were used to alter transgene expression. RESULTS:Delivery of three out of four orexigenic neuropeptides to the brain precipitated severe obesity. Cre-mediated excision of AgRP from the brain caused a return to baseline weight, confounded by tamoxifen-associated weight loss. Doxycycline-mediated suppression of AgRP in a TETOFF vector paused weight gain but did not elicit weight loss. Cumate induction of AgRP in the brain was unaffected by systemic administration, suggesting that cumate inadequately penetrates the blood-brain barrier. CONCLUSIONS:Brain-targeted delivery of orexigenic peptides induces obesity in mice. This allows for temporally controlled, convenient, and robust preclinical models of obesity. The implementation of genetic switches enabled suppression/removal of AgRP expression, but we unexpectedly observed that removal of hyperphagic stimuli does not elicit robust weight loss.

BACKGROUND:Pulmonary arterial hypertension (PAH) is high blood pressure in the lungs that originates from structural changes in small resistance arteries. A defining feature of PAH is the inappropriate remodeling of pulmonary arteries (PA) leading to right ventricle failure and death. Although treatment of PAH has improved, the long-term prognosis for patients remains poor, and more effective targets are needed. METHODS:Gene expression was analyzed by microarray, RNA sequencing, quantitative polymerase chain reaction, Western blotting, and immunostaining of lung and isolated PA in multiple mouse and rat models of pulmonary hypertension (PH) and human PAH. PH was assessed by digital ultrasound, hemodynamic measurements, and morphometry. RESULTS:Microarray analysis of the transcriptome of hypertensive rat PA identified a novel candidate, PBK (PDZ-binding kinase), that was upregulated in multiple models and species including humans. PBK is a serine/threonine kinase with important roles in cell proliferation that is minimally expressed in normal tissues but significantly increased in highly proliferative tissues. PBK was robustly upregulated in the medial layer of PA, where it overlaps with markers of smooth muscle cells. Gain-of-function approaches show that active forms of PBK increase PA smooth muscle cell proliferation, whereas silencing PBK, dominant negative PBK, and pharmacological inhibitors of PBK all reduce proliferation. Pharmacological inhibitors of PBK were effective in PH reversal strategies in both mouse and rat models, providing translational significance. In a complementary genetic approach, PBK was knocked out in rats using CRISPR/Cas9 editing, and loss of PBK prevented the development of PH. We found that PBK bound to PRC1 (protein regulator of cytokinesis 1) in PA smooth muscle cells and that multiple genes involved in cytokinesis were upregulated in experimental models of PH and human PAH. Active PBK increased PRC1 phosphorylation and supported cytokinesis in PA smooth muscle cells, whereas silencing or dominant negative PBK reduced cytokinesis and the number of cells in the G2/M phase of the cell cycle. CONCLUSIONS:PBK is a newly described target for PAH that is upregulated in proliferating PA smooth muscle cells, where it contributes to proliferation through changes in cytokinesis and cell cycle dynamics to promote medial thickening, fibrosis, increased PA resistance, elevated right ventricular systolic pressure, right ventricular remodeling, and PH.

The detection of superoxide anion (O2●−) in biological tissues remains challenging. Barriers to convenient and reproducible measurements include expensive equipment, custom probes, and the need for high sensitivity and specificity. The luminol derivative, L-012, has been used to measure O2●− since 1993 with mixed results and concerns over specificity. The goal of this study was to better define the conditions for use and their specificity. We found that L-012 coupled with depolymerized orthovanadate, a relatively impermeable tyrosine phosphatase inhibitor, yielded a highly sensitive approach to detect extracellular O2●−. In O2●− producing HEK-NOX5 cells, orthovanadate increased L-012 luminescence 100-fold. The combination of L-012 and orthovanadate was highly sensitive, stable, scalable, completely reversed by superoxide dismutase, and selective for O2●− generating NOXes versus NOX4, which produces H2O2. Moreover, there was no signal from cells transfected with NOS3 (NO●) and NOS2(ONOO−). To exclude the effects of altered tyrosine phosphorylation, O2●− was detected using non-enzymatic synthesis with phenazine methosulfate and via novel coupling of L-012 with niobium oxalate, which was less active in inducing tyrosine phosphorylation. Overall, our data shows that L-012 coupled with orthovanadate or other periodic group 5 salts yields a reliable, sensitive, and specific approach to measuring extracellular O2●− in biological systems.

Endothelin (ET)-1 is an endothelial-derived peptide that exerts biphasic effects on nitric oxide (NO) levels in endothelial cells such that acute exposure stimulates-while sustained exposure attenuates-NO production. Although the mechanism involved in the decrease in NO generation has been identified but the signaling involved in the acute increase in NO is still unresolved. This was the focus of this study. Our data indicate that exposing pulmonary arterial endothelial cells (PAEC) to ET-1 led to an increase in NO for up to 30min after which levels declined. These effects were attenuated by ET receptor antagonists. The increase in NO correlated with significant increases in pp60Src activity and increases in eNOS phosphorylation at Tyr83 and Ser1177. The ET-1 mediated increase in phosphorylation and NO generation were attenuated by the over-expression of a pp60Src dominant negative mutant. The increase in pp60Src activity correlated with a reduction in the interaction of Caveolin-1 with pp60Src and the calcineurin-mediated dephosphorylation of caveolin-1 at three previously unidentified sites: Thr91, Thr93, and Thr95. The calcineurin inhibitor, Tacrolimus, attenuated the acute increase in pp60Src activity induced by ET-1 and a calcineurin siRNA attenuated the ET-1 mediated increase in eNOS phosphorylation at Tyr83 and Ser1177 as well as the increase in NO. By using a Caveolin-1 celluSpot peptide array, we identified a peptide targeting a sequence located between aa 41-56 as the pp60Src binding region. This peptide fused to the TAT sequence was found to decrease caveolin-pp60Src interaction, increased pp60Src activity, increased eNOS pSer1177 and NO levels in PAEC and induce vasodilation in isolated aortic rings in wildtype but not eNOS knockout mice. Together, our data identify a novel mechanism by which ET-1 acutely increases NO via a calcineurin-mediated dephosphorylation of caveolin-1 and the subsequent stimulation of pp60Src activity, leading to increases in phosphorylation of eNOS at Tyr83 and Ser1177.

Pulmonary arterial hypertension (PAH) is a complex and fatal disorder characterized by an unrelenting increase in pulmonary arterial pressure. Excessive proliferation of pulmonary artery smooth muscle cells (PASMC) leads to increased vascular resistance and eventually right ventricular failure and death. Our lab has hypothesized that circulating Galectin-3 (Gal-3), a readily secreted b-galactoside-binding lectin protein, previously investigated as a biomarker of PAH, has a key role in the pathology of PAH. Co-culture experiments as well as recombinant protein supplementation show that soluble GAL-3 is biologically active and induces SMC growth and proliferation(P<.05). Inversely, inhibition of GAL-3 using blocking antibodies prevents this SMC proliferation. (p<.05) To test our hypothesis in-vivo we injected GAL-3 KO mice with a liver specific AAV overexpressing GAL-3 or GFP (control) and exposed them to sugen/hypoxia to induce PAH. Surprisingly our initial findings indicate no protection with liver GAL-3 overexpression compared to GFP transduced mice. Contrary to our hypothesis, while liver overexpression of GAL-3 was robustly increased, there was no evidence of GAL3 in the lungs or plasma of GAL3KO mice indicating it may not be robustly secreted from the hepatocyte, unlike what was observed in other cell types. This lack of circulating Gal-3 generated by liver overexpression revealed a knowledge gap in the mechanism of Gal-3 secretion into the circulation. To address this we have generated at a number of mutant forms of GAL3 that alter motifs proposed to be relevant to Gal-3 secretion. R186S prevents binding to the all but 1 of the 176 of GAL-3 binding glycans however this appears to have no impact on its uptake in GAL-3 KO cells. Similarly, L131A/L203A GAL-3 which prevents the oligomerization of GAL-3 by preventing interaction of the carbohydrate recognition domain with its n terminal binding domain (responsible for oligomerization) also maintains its ability to interact with these cells. These changes did not interfere with its secretion into the media. However, these interactions do appear to be altered somewhat, when a cell surface biotinylation assay is performed there is significantly less R185S on the cell surface compared to WT GAL-3. Our findings suggest that ECs and SMCs can secrete GAL-3 and exert pathological actions such as increasing proliferation in vitro. Our blocking antibody further suggests that this secreted GAL-3 is capable of regulating SMC proliferation and provides evidence for possible treatment of PAH. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Pulmonary Hypertension is a progressive vascular disease resulting from the tapering of pulmonary arteries causing high pulmonary arterial blood pressure and ultimately right ventricular failure. A defining characteristic of Pulmonary Hypertension is the excessive remodeling of pulmonary arteries that includes increased proliferation, vascular fibrosis and inflammation. There is no outward cure for Pulmonary Hypertension nor are there interventions that effectively impede or reverse pulmonary arterial remodeling, and pulmonary vascular research over the past several decades has sought to identify novel molecular mechanisms to target for therapeutic benefit. Galectin-3 is a carbohydrate binding lectin that is unique for its chimeric structure, comprised of an N-terminal oligomerization domain and a C-terminal carbohydrate-recognition domain. Galectin-3 is a regulator of modifications in cell behavior that contribute to aberrant pulmonary arterial remodeling including cell proliferation, inflammation, and fibrosis, but its role in Pulmonary Hypertension is poorly understood. In this review, we define Galectin-3 and summarize specific topics regarding the role of Galectin-3 expression in the development of Pulmonary Hypertension by providing evidence which supports the ability of Galectin-3 to influence reactive oxygen species production, NADPH enzyme expression, vascular inflammation and vascular fibrosis, all phenomena which contribute to pulmonary arterial remodeling and the development of Pulmonary Hypertension.

Acute lung injury (ALI) is characterized by lung vascular endothelial cell (EC) barrier compromise resulting in increased endothelial permeability and pulmonary edema. The infection of gram-negative bacteria that produce toxins like LPS is one of the major causes of ALI. LPS activates Toll-like receptor 4, leading to cytoskeleton reorganization, resulting in lung endothelial barrier disruption and pulmonary edema in ALI. However, the signaling pathways that lead to the cytoskeleton reorganization and lung microvascular EC barrier disruption remain largely unexplored. Here we show that LPS induces calpain activation and talin cleavage into head and rod domains and that inhibition of calpain attenuates talin cleavage, RhoA activation, and pulmonary EC barrier disruption in LPS-treated human lung microvascular ECs in vitro and lung EC barrier disruption and pulmonary edema induced by LPS in ALI in vivo. Moreover, overexpression of calpain causes talin cleavage and RhoA activation, myosin light chain (MLC) phosphorylation, and increases in actin stress fiber formation. Furthermore, knockdown of talin attenuates LPS-induced RhoA activation and MLC phosphorylation and increased stress fiber formation and mitigates LPS-induced lung microvascular endothelial barrier disruption. Additionally, overexpression of talin head and rod domains increases RhoA activation, MLC phosphorylation, and stress fiber formation and enhances lung endothelial barrier disruption. Finally, overexpression of cleavage-resistant talin mutant reduces LPS-induced increases in MLC phosphorylation in human lung microvascular ECs and attenuates LPS-induced lung microvascular endothelial barrier disruption. These results provide the first evidence that calpain mediates LPS-induced lung microvascular endothelial barrier disruption in ALI via cleavage of talin.

Pulmonary arterial hypertension is a rare and debilitating condition with a five-year survival rate of only 34% without treatment. The origins of pulmonary arterial hypertension are complex and incompletely understood and elevated pulmonary artery pressures result from excessive vascular remodeling due to functional changes in endothelial, vascular smooth muscle cells (VSMCs), and adventitial cells. Recent papers have explored the importance of metabolic switching of VSMCs in pulmonary hypertension in the transition towards a proliferative, apoptotic resistant phenotype which involves a shift from fatty acid oxidation to increased glycolysis. We hypothesized that ATPase Inhibitory Factor 1 (ATPIF1) in VSMCs could function as a metabolic switch that promotes a shift from fatty acid oxidation to glycolysis to increase the severity of pulmonary arterial hypertension. This hypothesis will be investigated using Western blot, Seahorse extracellular flux assays, qRT-PCR, and imaging of GFP-labelled ATPIF1. In preliminary data, we have cloned ATPIF1 and transfected cells to show overexpression of ATPIF1 decreases the maximal respiratory rate while increasing extracellular acidification, a measure of glycolysis. Future goals are to investigate the links between hypoxia, hypoxia-inducible factors and ATPIF1, the role of increased glycolysis in pulmonary smooth muscle cells, and ultimately whether ATPIF1 impacts of the development of pulmonary arterial hypertension in mice. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Pulmonary arterial hypertension (PAH) is a complex and fatal disorder characterized by an unrelenting increase in pulmonary arterial pressure. Excessive proliferation of pulmonary artery smooth muscle cells (PASMC) leads to increased vascular resistance and eventually right ventricular failure and death. Our laboratory has identified a key role for Galectin-3 (GAL-3) in PAH. However, the mechanisms by which GAL-3 alters PASMC behavior remains poorly understood. GAL-3 contains a functional BH1 like domain that has an NWGR sequence with high homology to the anti-apoptotic protein, BCL2, and this domain has previously been shown to be functional in cancer cell lines. Our hypothesis is GAL-3 upregulation plays an important role in driving PASMC proliferation through repression of apoptosis via this NWGR domain. Using adenoviral vector encoding the GAL-3 G182A mutation and isolated GAL-3 PASMCs from a GAL3 KO rat (RPASMC). Our in vitro studies show that overexpression of GAL-3 G182A causes a decrease in viability upon treatment overnight with 0.5% serum containing media(p<.001) compared to normal media (p=.840). When exposed to apoptotic stimuli (TNFα, Cycloheximide) GAL-3 G182A overexpressing GAL-3 KO RPASMCs had significantly (p<.001) decreased vitality. Interestingly however, this domain also seems to regulate non-apoptotic related events such as cell attachment. Our previous work had shown that GAL-3 is readily excreted protein, and co-culture experiments as well as recombinant protein supplementation show that soluble GAL-3 is biologically active and induces SMC growth and proliferation(P<.05). Further experimentation also shows that inhibition of GAL-3 using blocking antibodies prevents SMC proliferation. (p<.05) To test this hypothesis in-vivo we injected GAL-3 KO mice with a liver specific AAV overexpressing GAL-3, or GFP (control) and exposed them to sugen/hypoxia to induce PAH. Surprisingly our initial findings indicate a slight protection with liver GAL-3 overexpression when compared to wt mice.(p<.05) Also very interestingly, while liver overexpression of GAL-3 was very high there was no evidence of GAL3 in the lungs or plasma of GAL3KO mice indicating it may not be secreted from the liver in sufficient amounts unlike what was observed in other cell types. Overall our data suggests that the NWGR domain of GAL-3 is an important regulator of PASMC survivability and the blocking antibody suggests that secreted GAL-3 is capable of regulating SMC proliferation, however it does not appear that hepatocytes secrete sufficient GAL-3 for it to circulate and play a role in the lung vasculature.

Pneumolysin (PLY) is a bacterial pore forming toxin and primary virulence factor of Streptococcus pneumonia, a major cause of pneumonia. PLY binds cholesterol-rich domains of the endothelial cell (EC) plasma membrane resulting in pore assembly and increased intracellular (IC) Ca2+ levels that compromise endothelial barrier integrity. Caveolae are specialized plasmalemma microdomains of ECs enriched in cholesterol. We hypothesized that the abundance of cholesterol-rich domains in EC plasma membranes confers cellular susceptibility to PLY. Contrary to this hypothesis, we found increased PLY-induced IC Ca2+ following membrane cholesterol depletion. Caveolin-1 (Cav-1) is an essential structural protein of caveolae and its regulation by cholesterol levels suggested a possible role in EC barrier function. Indeed, Cav-1 and its scaffolding domain peptide protected the endothelial barrier from PLY-induced disruption. In loss of function experiments, Cav-1 was knocked-out using CRISPR-Cas9 or silenced in human lung microvascular ECs. Loss of Cav-1 significantly enhanced the ability of PLY to disrupt endothelial barrier integrity. Rescue experiments with re-expression of Cav-1 or its scaffolding domain peptide protected the EC barrier against PLY-induced barrier disruption. Dynamin-2 (DNM2) is known to regulate caveolar membrane endocytosis. Inhibition of endocytosis, with dynamin inhibitors or siDNM2 amplified PLY induced EC barrier dysfunction. These results suggest that Cav-1 protects the endothelial barrier against PLY by promoting endocytosis of damaged membrane, thus reducing calcium entry and PLY-dependent signaling.

Pulmonary Arterial Hypertension (PAH) is a progressive disease that is caused by high blood pressure in the lungs that originates from increased resistance of small pulmonary arteries (PA). A defining characteristic of PAH is vascular smooth muscle cell (VSMC) proliferation and remodeling of PA, that eventually results in right ventricular failure and death. The hyperproliferative nature of vascular cells in PAH shares many characteristics with cancer cells such as sustained proliferative signaling, changes in hypoxia signaling and cellular metabolism. Using microarray analysis, we discovered a novel gene, PDZ-Binding Kinase (PBK) that is upregulated in hypertensive PA. PBK is a serine/threonine kinase that has important roles in mitosis and cell proliferation. Also, elevated expression of PBK is associated with numerous aggressive cancers suggesting that it may be an important contributor to PAH. Our hypothesis is that PBK has a functional role in the pathogenesis of PAH but the therapeutic utility of targeting PBK in PAH and the mechanisms by which PBK promotes pulmonary vascular remodeling have not been studied. To investigate the role of PBK in PAH, we performed immunostaining, and found that PBK was highly upregulated in pulmonary arterial smooth muscle in the lungs of two experimental PAH rat models (MCT; Su/H), in the Su/H mouse model, as well as in human PAs and lungs with PAH. Furthermore, human pulmonary arterial smooth cells (HPASMCs) overexpressing PBK showed increased proliferation, while silencing PBK or in vitro pharmacological inhibition significantly reduced HPASMC proliferation. To determine whether PBK plays an important role in PA remodeling and PAH in vivo, we next utilized PBK inhibitor (OTS-514) to treat MCT-induced PAH rats in a reversal treatment method and Su/H Rats and Mouse in a preventative treatment. In all of the PAH animal models, right ventricle (RV) thickness, velocity time integral (VTI, index of PA stiffness), right ventricular systolic pressure (RVSP), and the Fulton Index were significantly improved in the presence of the PBK inhibitor. To complement our pharmacological studies with a genetic approach, we have generated PBK KO rats to investigate whether genetic ablation of PBK protects against the development of PAH. Taken together, these data support the hypothesis, that PBK drives pulmonary artery smooth muscle proliferation leading to abnormal vascular remodeling and the development of PAH. Our findings advance the utility of novel therapeutic approaches targeting PBK to improve the morbidity and mortality associated with PAH.

AIMS:Proliferation of vascular smooth muscle cells (VSMCs) is a hallmark of pulmonary hypertension (PH). Proliferative cells utilize purine bases from the de novo purine synthesis (DNPS) pathways for nucleotide synthesis; however, it is unclear whether DNPS plays a critical role in VSMC proliferation during development of PH. The last two steps of DNPS are catalysed by the enzyme 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/inosine monophosphate cyclohydrolase (ATIC). This study investigated whether ATIC-driven DNPS affects the proliferation of pulmonary artery smooth muscle cells (PASMCs) and the development of PH.METHODS AND RESULTS:Metabolites of DNPS in proliferative PASMCs were measured by liquid chromatography-tandem mass spectrometry. ATIC expression was assessed in platelet-derived growth factor-treated PASMCs and in the lungs of PH rodents and patients with pulmonary arterial hypertension. Mice with global and VSMC-specific knockout of Atic were utilized to investigate the role of ATIC in both hypoxia- and lung interleukin-6/hypoxia-induced murine PH. ATIC-mediated DNPS at the mRNA, protein, and enzymatic activity levels were increased in platelet-derived growth factor-treated PASMCs or PASMCs from PH rodents and patients with pulmonary arterial hypertension. In cultured PASMCs, ATIC knockdown decreased DNPS and nucleic acid DNA/RNA synthesis, and reduced cell proliferation. Global or VSMC-specific knockout of Atic attenuated vascular remodelling and inhibited the development and progression of both hypoxia- and lung IL-6/hypoxia-induced PH in mice.CONCLUSION:Targeting ATIC-mediated DNPS compromises the availability of purine nucleotides for incorporation into DNA/RNA, reducing PASMC proliferation and pulmonary vascular remodelling and ameliorating the development and progression of PH.

Pulmonary Arterial Hypertension (PAH) is a progressive vascular disease arising from the narrowing of pulmonary arteries (PA) resulting in high pulmonary arterial blood pressure and ultimately right ventricular (RV) failure. A defining characteristic of PAH is the excessive remodeling of PA that includes increased proliferation, inflammation, and fibrosis. There is no cure for PAH nor interventions that effectively impede or reverse PA remodeling, and research over the past several decades has sought to identify novel molecular mechanisms of therapeutic benefit. Galectin-3 (Gal-3; Mac-2) is a carbohydrate-binding lectin that is remarkable for its chimeric structure, comprised of an N-terminal oligomerization domain and a C-terminal carbohydrate-recognition domain. Gal-3 is a regulator of changes in cell behavior that contribute to aberrant PA remodeling including cell proliferation, inflammation, and fibrosis, but its role in PAH is poorly understood. Herein, we summarize the recent literature on the role of Gal-3 in the development of PAH and provide experimental evidence supporting the ability of Gal-3 to influence reactive oxygen species (ROS) production, NOX enzyme expression, inflammation, and fibrosis, which contributes to PA remodeling. Finally, we address the clinical significance of Gal-3 as a target in the development of therapeutic agents as a treatment for PAH.

Macrophage infiltration into the lungs is a characteristic of pulmonary hypertension (PH). Glycolysis is the main metabolic pathway for macrophage activation. However, the effect of macrophage glycolysis on the development of PH remains unknown. We investigated the effect of 6‐phosphofructo‐2‐kinase/fructose‐2,6‐bisphosphatase 3 (PFKBF3), a critical enzyme of macrophage glycolysis, on PH development.

Pulmonary Arterial Hypertension (PAH) is an insidious disease that develops gradually and becomes symptomatic only in the latter stages. In PAH, along with increased pulmonary artery (PA) pressure, the PAs in the lungs continue to become more muscular, narrower restricting blood flow through the lungs. Increased proliferation of pulmonary arterial smooth muscle cells (PASMC) are largely responsible for the development PA hypertrophy. Because excessive proliferation of PASMC in PAH shares many characteristics with other hyperproliferative diseases such as cancer, there is a growing interest in repurposing therapeutic targets in cancer, for the treatment of PAH. In preliminary studies, we screened a microarray of isolated PAs from control and monocrotaline (MCT)‐induced PAH rats for novel genes that may be responsible for the proliferation of PASMCs in PAH. We found that the gene PDZ‐Binding Kinase (PBK) was significantly higher in PAs from MCT rats versus controls. PBK (also known as TOPK or T‐cell‐originated Lymphokine‐activated killer protein kinase) is a serine/threonine kinase that plays a key role in several types of cancer. Although PBK levels are typically very low in healthy tissues, expression levels are significantly increased in cancer cells, which correlates with a poor prognosis of breast, gastric and lung cancers. We performed immunostaining, and found that PBK was highly upregulated and concentrated in the smooth muscle layer of both PAH rats (MCT and Sugen/Hypoxia induced) as well as in human PAs with PAH. To determine a functional role for PBK in PASMCs, we generated an adenovirus encoding PBK and found that increased expression stimulated PASMC proliferation and resistance to apoptosis. In contrast, silencing PBK or in vitro pharmacological inhibition (HI‐TOPK‐032, 2μM) significantly (p<0.05; n=5) reduced PASMC proliferation and increased cell death. Furthermore, the specific PBK inhibitor OTS514 (5mg/kg/day for 14 days) reduced right ventricle hypertrophy (Fulton Index) and improved PA remodeling in the MCT‐induced model of PAH. Collectively, these findings suggest that PBK drives pulmonary artery smooth muscle proliferation leading to abnormal vascular remodeling and the development of PAH.Support or Funding InformationAHA 19PRE34450087R01HL125926‐03