Academic literature on the topic 'TGFbeta pathway'

In C. elegans, the TGFbeta-like type II receptor daf-4 is required for two distinct signaling pathways. In association with the type I receptor daf-1, it functions in the dauer pathway. In addition, it is also required for body size determination and male tail patterning, roles which do not require daf-1. In an effort to determine how two different signals are transmitted through daf-4, we looked for other potential signaling partners for DAF-4. We have cloned and characterized a novel type I receptor and show that it is encoded by sma-6. Mutations in sma-6 generate the reduced body size (Sma) and abnormal mail tail (Mab) phenotypes identical to those observed in daf-4 and sma-2, sma-3, sma-4 mutants (C. elegans Smads), indicating that they function in a common signaling pathway. However, mutations in sma-6, sma-2, sma-3, or sma-4 do not produce constitutive dauers, which demonstrates that the unique biological functions of daf-4 are mediated by distinct type I receptors functioning in parallel pathways. We propose that the C. elegans model for TGFbeta-like signaling, in which distinct type I receptors determine specificity, may be a general mechanism of achieving specificity in other organisms. These findings distinguish between the manner in which signaling specificity is achieved in TGFbeta-like pathways and receptor tyrosine-kinase (RTK) pathways.

Abstract Pluripotent stem cells derived from patients, including embryonic stem (ES) cells and “induced pluripotent stem” (iPS) cells, are a promising area of regenerative medical research. A major roadblock toward human clinical therapies using ES cells or iPS cells is to define the factors that direct ES cell differentiation into lineage specific cells. We previously established a simple and efficient human embryonic stem cell (hESC) differentiation system to generate CD34+/CD31+ progenitor cells that gave rise to hematopoietic and endothelial cells (Nat Biotech.25:317, 2007). To advance potential clinical application and to define the effects of growth factors on hematopoietic and vascular differentiation, we assessed hESC differentiation on human feeder cells in serum-free condition without intermediate embryoid body (EB) formation. We investigated the roles of BMPs, TGFbeta, VEGF, and FGF2 in directing hESC differentiation. Growth factors were added into culture at different time points to test their stage specific roles. Our study demonstrated that BMP proteins, including BMP2, BMP4, and BMP7, but not BMP9, had synergic effects to VEGF and FGF-2 on hESC differentiation to CD34+/CD31+ progenitor cells. BMP4 was essential to initial CD34+/CD31+ cell development, whereas VEGF and FGF2 promoted the differentiation in later stage, suggesting the sequential roles of BMP4, VEGF and FGF2 in directing hESC differentiation to CD34+/CD31+ progenitor cells. TGFbeta or activin promoted hESC differentiation into CD34+/CD31− cells that were unable to give rise to hematopoietic, endothelial, and smooth muscle cells. Furthermore, TGFbeta or activin activated Smad2/3 signaling, and suppressed BMP4-induced CD34+/CD31+ cells. Microarray analysis revealed that BMP4-induced CD34+ cells expressed hematopoietic, endothelial and smooth muscle genes, including GATA2, gamma globins, VE-Cad, KDR, CD31, Tie2, and aortic smooth muscle actin, whereas TGFbeta-induced CD34+ cells expressed pluripotent markers and endoderm markers, including Oct3/4, Sox2, and Nanog, HHEX, GATA6, and FoxA2. Both canonical BMP signaling (Smad1/5/8-dependent) and non-canonical BMP signaling (p38 MAPK and p42 ERK pathway) were activated by BMP4 in hESCs. Dorsomorphin specifically inhibited BMP4-mediated phosphorylation of Smad1/5/8, and blocked hESC differentiation into CD34+/CD31+ cells. In summary, BMPs and TGFbeta regulate distinct populations of CD34+ cells in hESCs. BMP-Smad1/5/8 pathway is critical for hematopoietic and vascular progenitor development.

Abstract Intro: Mutations in TGFbR1, TGFbR2 and SMAD3 are associated with familial thoracic aortic aneurysms and aortic dissections (TAAD). These patients offer an opportunity to study their immune development. Methods: PBMC from TAAD (n=9) and controls (CT, n=8) were analyzed by FACS. Th1 (IFNg) and Th17 (IL17A) were determined with intracellular cytokine staining. Foxp3+ Tregs were detected with anti-Foxp3. CD19+ were analyzed for naive (IgD+CD27-), unswitched (IgD+CD27+) and switched memory (IgD-CD27+). Plasmacytoid (CD303+pDC) and myeloid (CD1c+mDC) were defined within lineage-1 negative population. Results: %CD3-CD16+NK, CD3+CD16+NKT, CD4+, CD8+ and CD4+CD45RA+ in TAAD were similar to HC. Average %CD19+ (20.8vs7.3, p=0.006) and naive B cells (81.3vs66.6, p=0.004) were higher in TAADvsCT. The unswitched were similar but the switched B cells were lower (8.6vs15.5, p=0.01). While the %Tregs were similar, there was a remarkable reduction (1/2-3 folds, p<0.05) in Foxp3 concentration based on median fluorescence intensity of Foxp3 in TAAD. There was a significant reduction of %Th17 (0.14vs0.61, p=0.01), while the Th1 were similar. %pDC (9.4vs24.1, p=0.009) and %mDC (11.4vs17.9, p=0.01) were also lower in TAAD. Conclusions: These results demonstrate the involvement of TGFbeta signaling in B cells, DCs, Th17 and Treg development. Further studies and monitoring of the clinical effects of these immunological perturbations are needed to appreciate the impact of their underlying disease.

Abstract Hepsin (encoded by HPN gene) is a type II transmembrane serine protease, which is commonly overexpressed in carcinomas of prostate and breast. Hepsin protein is known to be stabilized by Ras-MAPK pathway signaling, and downstream, this protease regulates the degradation of extracellular matrix (ECM) components and activates growth factor pathways, including hepatocyte growth factor (HGF) and transforming growth factor beta (TGF beta) pathway. However, the impact of the hepsin-dependent signaling on cell proliferation and tumor growth is not well-understood. Therefore, we sought to clarify the role of hepsin during these events using engineered breast cancer cell lines, Hpn CRISPR knockout mouse model crossed with Wap-Myc breast cancer mouse model, and patient-derived explant cultures (PDEC)s from human breast tumors. We isolated Wap-Myc; Hpn-/- mammary tumor cells and made orthotopic transplantation into syngeneic wild-type recipient mice. The resulting Wap-Myc tumors that lack hepsin had reduced size both in primary and metastatic site compared to tumors derived from Wap-Myc; Hpn+/+ tumor cells. This decrease in growth was accompanied by downregulation in TGF beta and EGFR signaling as well as substantial reduction in total EGFR protein level. We further demonstrated that in 3D culture conditions overexpression of hepsin induced cell proliferation, which was TGF beta 1 and EGFR signaling-dependent, while PDECs treated with hepsin inhibitory antibodies and small molecules had decreased EGFR and TGF beta signaling activity and reduction in proliferation marker expression. Taken together, this study demonstrates a role for hepsin as a regulator of cell proliferation and tumor growth through TGF beta and EGFR pathways and may provide an interesting druggable upstream target to inhibit TGF beta and EGFR pathways in breast cancer. Citation Format: Topi A. Tervonen, Denis Belitškin, Pauliina Munne, Shishir M. Pant, Ilida Suleymanova, Kati Belitškina, Jeroen Pouwels, Juha Klefström. Serine protease hepsin regulates tumor growth via TGFbeta-EGFR signaling axis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 834.

TGFbeta-related factors are critical regulators of vertebrate mesoderm development. However, the signalling cascades required for their function during this developmental process are poorly defined. Tlx-2 is a homeobox gene expressed in the primitive streak of mouse embryos. Exogenous BMP-2 rapidly activates Tlx-2 expression in the epiblast of E6.5 embryos. A Tlx-2 promoter element responds to BMP-2 signals in P19 cells, and this response is mediated by BMP type I receptors and Smad1. These results suggest that Tlx-2 is a downstream target gene for BMP signalling in the primitive streak where BMP-4 and other TGFbeta-related factors are expressed. Furthermore, disruption of Tlx-2 function leads to early embryonic lethality. Similar to BMP4 and ALK3 mutants, the mutant embryos display severe defects in primitive streak and mesoderm formation. These experiments thus define a BMP/Tlx-2 signalling pathway that is required during early mammalian gastrulation.

Gene expression in the pharyngeal muscles of Caenorhabditis elegans is controlled in part by organ-specific signals, which in the myo-2 gene target a short DNA sequence termed the C subelement. To identify genes contributing to these signals, we performed a yeast one-hybrid screen for cDNAs encoding factors that bind the C subelement. One clone recovered was from daf-3, which encodes a Smad most closely related to vertebrate Smad4. We demonstrated that DAF-3 binds C subelement DNA directly and specifically using gel mobility shift and DNase1 protection assays. Mutation of any base in the sequence GTCTG interfered with binding in the gel mobility shift assay, demonstrating that this pentanucleotide is a core recognition sequence for DAF-3 binding. daf-3 is known to promote formation of dauer larvae and this activity is negatively regulated by TGFbeta-like signaling. To determine how daf-3 affects C subelement enhancer activity in vivo, we examined expression a gfp reporter controlled by a concatenated C subelement oligonucleotide in daf-3 mutants and other mutants affecting the TGFbeta-like signaling pathway controlling dauer formation. Our results demonstrate that wild-type daf-3 can repress C subelement enhancer activity during larval development and, like its dauer-promoting activity, daf-3's repressor activity is negatively regulated by TGFbeta-like signaling. We have examined expression of this gfp reporter in dauer larvae and have observed no daf-3-dependent repression of C activity. These results suggest daf-3 directly regulates pharyngeal gene expression during non-dauer development.

Cell signalling determines physiological responses to many cellular stimuli and environmental changes. The transforming growth factor-beta (TGFβ)/bone morphogenetic protein (BMP) signalling pathways begin by binding of ligand to the heterodimeric receptor complex, followed by activation of Smads that translocate to the nucleus to regulate transcription of genes that further mediate cellular physiology. The TGFβ/BMP pathways are very important for proper tissue development and homeostasis, thus precise spatial and temporal regulation of the signalling pathway is required and achieved by many positive and negative signalling regulators. This thesis work identified the liver kinase B1 (LKB1) pathway as a negative regulator of TGFβ/BMP signalling pathways. In the first paper, we established LKB1 as a negative regulator of TGFβ signalling and TGFβ-induced epithelial to mesenchymal transition (EMT). LKB1 impairs Smad4 binding capacity to DNA leading to suppressed TGFβ-activated gene transcription. The second paper describes further the mechanism of LKB1 negative regulation on BMP signalling, by mediating BMP type I receptor degradation resulting in inhibition of BMP-induced cell differentiation. Downstream of LKB1, salt inducible kinase 1 (SIK1) is a TGFβ target gene and its expression is up-regulated by Smad2/3/4-mediated gene transcription. The third paper elucidates the mechanism of SIK1 transcriptional induction via an enhancer element located 3’ of the gene and SIK1-mediated type I TGFβ receptor degradation, which requires the activity of Smad7 and of the Smurf2 ubiquitin ligase. The fourth manuscript finds sucrose non-fermenting (SNF) 1-like kinase 2 (NUAK2) as another TGFβ target gene and its up-regulation results in modification of the mammalian target of rapamycin (mTOR) pathway that controls protein synthesis. NUAK2 cooperates with LKB1 leading to Raptor phosphorylation and inhibition of mTOR-mediated protein synthesis. Collectively, this thesis work has provided a functional link between two important signalling pathways, the metabolic LKB1 pathway and TGFβ/BMP pathway.

La régénération musculaire s’appuie sur une réserve de cellules souches résidant dans le muscle appelées cellules satellites (MuSCs). Les MuSCs sont quiescentes et peuvent s’activer à la suite d’une blessure du muscle afin de former des progéniteurs amplificateurs (myoblastes) qui se différencieront et fusionneront pour former de nouvelles myofibres. Durant ce processus, un réseau complexe de voies de signalisation est impliqué, parmi lequel la signalisation du facteur de croissance transformant bêta (TGFβ) joue un rôle fondamental. Précédents rapports ont proposé de nombreuses fonctions pour la signalisation TGFβ dans les cellules musculaires, comme leur quiescence, activation et différenciation, mais l’impact de TGFβ sur la fusion de myoblastes n’a jamais été étudié. Dans cette étude, nous avons montré que cette signalisation réduit la fusion des cellules musculaires indépendamment de leur différenciation. Au contraire, l’inhibition de la signalisation TGFβ accroît la fusion cellulaire et favorise les ramifications entre myotubes. Une pharmaco-modulation de la voie in vivo perturbe la régénération musculaire après blessure. Une addition exogène de la protéine TGFβ conduit à une perte de fonction du muscle, tandis que l’inhibition de la voie induit la formation de myotubes géants. Les analyses transcriptomiques et fonctionnelles ont montré que TGFβ agit sur la dynamique de l’actine afin de réduire la diffusion cellulaire à travers une modulation des protrusions à base d’actine. Nos résultats ont donc révélé une voie de signalisation qui limite la fusion de myoblastes et ajoutent un nouveau niveau de compréhension sur la régulation moléculaire de la myogenèse
Muscle regeneration relies on a pool of muscle-resident stem cells called satellite cells (MuSCs). MuSCs are quiescent and can activate following muscle injury to give rise to transient amplifying progenitors (myoblasts) that will differentiate and finally fuse together to form new myofibers. During this process, a complex network of signalling pathways is involved, among which, Transforming Growth Factor beta (TGFβ) signalling cascade plays a fundamental role. Previous reports proposed several functions for TGFβ signalling in muscle cells including quiescence, activation and differentiation. However, the impact of TGFβ on myoblast fusion has never been investigated. In this study, we show that TGFβ signalling reduces muscle cell fusion independently of the differentiation step. In contrast, inhibition of TGFβ signalling enhances cell fusion and promotes branching between myotubes. Pharmacological modulation of the pathway in vivo perturbs muscle regeneration after injury. Exogenous addition of TGFβ protein results in a loss of muscle function while inhibition of the TGFβ pathway induces the formation of giant myofibres. Transcriptome analyses and functional assays revealed that TGFβ acts on actin dynamics to reduce cell spreading through modulation of actin-based protrusions. Together our results reveal a signalling pathway that limits mammalian myoblast fusion and add a new level of understanding to the molecular regulation of myogenesis

Head and Neck Squamous Cell Carcinoma (HNSCC) represents the sixth most common cancer worldwide, with about 550,000 new cases/year. Despite the development of precise and accurate surgery followed by radio- and/or chemo-therapy, in the last decade patients’ overall survival was only slightly improved. In particular, only 40-50% of patients with advanced HNSCC will survive for 5 years. The main worse prognostic event is considered the onset of loco-regional and distant recurrences, that is also accepted as surrogate markers of patients’ overall survival. HNSCC is a heterogeneous disease and, although many studies have been conducted to clarify the molecular mechanisms behind the development of local or distant metastasis, no clear molecular mediators of recurrence formation have been identified and no valid biomarkers exist to identify and treat patients at high-risk of recurrence. We aimed to fill this gap taking advantage of an unbiased approach in which we evaluated microRNA (miRNA) expression profile in a cohort of HNSCC primary tumours from recurrent and non-recurrent patients. We identified and validated a four-miRNA signature, composed by miR-1, miR-9, miR-133a and miR-150 that could be used as biomarker of recurrence. All these miRNAs are not only well-known molecular modulators of cell plasticity in different tumours, but intriguingly in our HNSCC model they are also able to classify HNSCC patients at high- or low-risk of recurrence formation. We demonstrated that these miRNAs collectively impinge on the epithelial-mesenchymal transition process. In silico and wet lab approaches showed that miR-9, expressed at high levels in recurrent HNSCC, targets the epithelial genes SASH1 and KRT13, while miR-1, miR-133a and miR-150, expressed at low levels in recurrent HNSCC, collectively target SP1 and TGF pathways. In vivo, a six-genes signature comprising the above targets, consistently predicts low progression free- and overall-survival in different panels of HNSCC samples. This is of particular clinical relevance, since the detection of this gene signature in tumours specimens could identify patients with poor prognosis who may benefit for a more accurate targeted therapy. In a preclinical model of HNSCC recurrence, the combined pharmacological inhibition of SP1 and TGF pathways, when timely administered, induced HNSCC cell death and prevented recurrence formation. By integrating different experimental approaches, we identified critical mediators of recurrence formation in advanced HNSCC. Since both SP1 and TGF pathways could be pharmacologically targeted, their combined inhibition may merit to be considered for future clinical development.

La spondyloarthrite (SpA) est une maladie inflammatoire chronique fréquente. Chez l'Homme, l'association entre l'allèle HLA-B27 du complexe majeur d'histocompatibilité de classe-I (CMH-I) et le développement de la maladie a été démontrée il y a 50 ans, 70 à 90% des patients atteints de SpA étant porteurs de cet allèle. Cependant, le rôle exact du HLA-B27 dans la physiopathologie de la SpA reste inconnu. Le modèle du rat transgénique pour le HLA-B27 et la β2-microglobuline humaine (hβ2m) (rat B27), qui développe des manifestations similaires à la maladie humaine, a permis d'éclaircir certains aspects de la question. Notamment, l'implication des lymphocytes T (LT) CD4+ dans la SpA a pu être mise en évidence. Chez le rat B27, les LT CD4+ régulateurs (Treg) présentent un déséquilibre de la balance interleukine-10/interleukine-17 (IL-10/IL-17), respectivement anti- et pro- inflammatoires. D'autre part, une expansion de la sous-population des LT CD4+ helper 17 (Th17) pro-inflammatoires, producteurs d'IL-17 est observée aussi bien chez le rat B27 que chez les patients. Dans le but d'étudier les effets non-canoniques du HLA-B27, un modèle de Drosophila melanogaster transgénique pour le HLA-B27 et la hβ2m a été développé et a permis de mettre en évidence qu'une interaction entre le HLA-B27 et des récepteurs de type I de la voie BMP/TGFβ (BMPR1) altérait la formation des veines transversales de l'aile. Dans ce modèle, il a précédemment été montré une interaction entre le HLA-B27 et le récepteur Saxophone (Sax) conduisant à l'augmentation de la signalisation BMP. Notre étude a complété ces résultats en montrant qu'une signalisation aberrante passant par le BMPR1 Baboon (Babo) de la voie de l'activine/TGFβ participait aussi au phénotype anormal induit par l'expression du HLA-B27. Pour tenter d'extrapoler ces résultats à un mécanisme de pathogénicité du HLA-B27 au cours de la SpA, nous avons tout d'abord démontré qu'il existait une interaction spécifique entre HLA-B27 et l'activin receptor-like kinase 2 (ALK2), orthologue de Sax d'une part, mais aussi avec ALK5, le récepteur de type 1 au TGFβ orthologue de Babo dans les lymphocytes de rat B27. L'étude de SMAD2/3, le principal transducteur du signal TGFβ, dans les LT de rats B27 et non transgéniques révèle une phosphorylation basale plus faible et une amplitude de phosphorylation plus forte après stimulation par le TGFβ1. De façon concordante, nous avons observé que certains gènes induits par la signalisation TGFβ et impliqués dans la différenciation des Treg et Th17 (Foxp3, Rorc, Runx1) avaient une expression augmentée dans les LT CD4+ naïfs (Tn) de rat B27. Ensemble, ces résultats indiquent une possible activation précoce de la voie TGFβ dans les Tn des rats B27 suivie d'une boucle de rétrocontrôle négatif. De façon intéressante, le gène Tgfb1 lui-même était diminué. Compte tenu de l'importance du TGFβ1 autocrine produit par les LT pour prévenir l'inflammation chronique, ces observations ouvrent des perspectives pour mieux comprendre le rôle du HLA-B27 dans le développement de la SpA. Nous pourrons en particulier, étudier de façon plus approfondie la réponse des Tn de rats B27 au TGFβ1 par des méthodes multi-omiques (transciptomique, phosphoprotéomique, protéomique...). Enfin, compte tenu du rôle essentiel du TGFβ1 autocrine dans le maintien des profils Treg et Th17, une étude de la plasticité des Treg et Th17 des rats B27 serait pertinentes pour mieux comprendre la physiopathologie de la SpA
Spondyloarthritis (SpA) is a common chronic inflammatory disease. In human, the association between the HLA-B27 allele of the class-I major histocompatibility complex (MHC-I) and the development of this disease was demonstrated 50 years ago, with 70-90% of SpA patients carrying this allele. However, the exact role of HLA-B27 in the pathophysiology of SpA remains unknown. The model of rat transgenic for HLA-B27 and the human β2-microglobulin (hβ2m) (B27 rat), which develops manifestations similar to the human disease, has shed light on certain aspects of the question. In particular, the involvement of CD4+ T lymphocytes in SpA has been demonstrated. In the B27 rat, regulatory CD4+ T lymphocytes (Treg) exhibit an imbalance of the interleukin-10/interleukin-17 (IL-10/IL-17) ratio, which are anti-inflammatory and pro-inflammatory, respectively. On the other hand, an expansion of the sub-population of pro-inflammatory CD4+ T helper 17 (lymphocytes Th17), which produce IL-17, was observed in both B27 rats and SpA patients. To study the non-canonical effects of HLA-B27, a Drosophila melanogaster model transgenic for HLA-B27 and hβ2m was developed and demonstrated that an interaction between HLA-B27 and type I receptors of the BMP/TGFβ pathway (BMPR1s) altered the formation of the wing transverse veins. In this model, an interaction between HLA-B27 and the Saxophone (Sax) receptor has previously been shown to lead to increased BMP signalling. Our study complemented these results by showing that aberrant signaling via the BMPR1 Baboon (Babo) of the activin/TGFβ pathway also contributed to the abnormal phenotype induced by HLA-B27 expression. In an attempt to extrapolate these results to a mechanism of HLA-B27 pathogenicity in SpA, we first demonstrated that there was a specific interaction between HLA-B27 and activin receptor-like kinase 2 (ALK2), the orthologue of Sax, and also with ALK5, the type 1 receptor for TGFβ orthologue of Babo, in rat B27 lymphocytes. Study of SMAD2/3, the main transducer of the TGFβ signal, in T lymphocytes from B27 and nontransgenic rats revealed a lower basal phosphorylation and a higher amplitude of phosphorylation after stimulation by TGFβ1. Concordantly, we observed that several genes induced by TGFβ signaling and involved in Treg and Th17 differentiation (Foxp3, Rorc, Runx1) had increased expression in naive CD4+ T lymphocytes (Tn) from B27 rats. Taken together, these results indicate a possible early activation of the TGFβ pathway in B27 rat Tn followed by a negative feedback loop. Interestingly, the Tgfb1 gene itself was decreased. Given the importance of autocrine TGFβ1 produced by T lymphocytes in preventing chronic inflammation, these observations open up prospects for a better understanding of the role of HLA-B27 in the development of SpA. In particular, we propose to study in greater depth the response of Tn from B27 rats to TGFβ1 using multi-omics methods (transciptomic, phosphoproteomic, proteomic). Finally, given the essential role of autocrine TGFβ1 in the maintenance of Treg and Th17 profiles, a study of the plasticity of Treg and Th17 in B27 rat would be relevant to a better understanding of the pathophysiology of SpA

Pulmonary arterial hypertension (PAH) is a cardiovascular disorder associated with enhanced proliferation and suppressed apoptosis of pulmonary arterial smooth muscle cells (PASMCs). Heterozygous mutations in the type II receptor for bone morphogenetic protein (BMPR2) underlie the majority of the inherited and familial forms of PAH. The transforming growth factor beta (TGFbeta) pathway is activated in both human and experimental models of PAH. However, how these factors exert pro-proliferative and anti-apoptotic responses in PAH remains unclear. Using mouse primary PASMCs derived from knock-in mice, we demonstrated that BMPR-II dysfunction promotes the activation of small mothers against decapentaplegia-independent mitogen-activated protein kinase (MAPK) pathways via TGFbeta-associated kinase 1 (TAK1), resulting in a pro-proliferative and anti-apoptotic response. Inhibition of the TAK1-MAPK axis rescues abnormal proliferation and apoptosis in these cells. In both hypoxia and monocrotaline-induced PAH rat models, which display reduced levels of bmpr2 transcripts, this study further indicates that the TGFbeta-MAPK axis is activated in lungs following elevation of both expression and phosphorylation of the TAK1 protein. In ex vivo cell-based assays, TAK1 inhibits BMP-responsive reporter activity and interacts with BMPR-II receptor. In the presence of pathogenic BMPR2 mutations observed in PAH patients, this interaction is greatly reduced. Taken together, these data suggest dysfunctional BMPR-II responsiveness intensifies TGFbeta-TAK1-MAPK signalling and thus alters the ratio of apoptosis to proliferation. This axis may be a potential therapeutic target in PAH.