Renin-Angiotensin System in Lung Tumor and Microenvironment Interactions

Abstract

The mechanistic involvement of the renin-angiotensin system (RAS) reaches beyond cardiovascular physiopathology. Recent knowledge pinpoints a pleiotropic role for this system, particularly in the lung, and mainly through locally regulated alternative molecules and secondary pathways. Angiotensin peptides play a role in cell proliferation, immunoinflammatory response, hypoxia and angiogenesis, which are critical biological processes in lung cancer. This manuscript reviews the literature supporting a role for the renin-angiotensin system in the lung tumor microenvironment and discusses whether blockade of this pathway in clinical settings may serve as an adjuvant therapy in lung cancer.

Keywords: hypoxia; lung cancer; renin-angiotensin; tumor microenvironment.

Figure 1

Schematic representation of the renin-angiotensin system, its interaction with tumor hypoxia and angiogenesis and subsequent functional impact on tumor phenotype. Full line arrows represent positive effects, whereas dashed lines with blunt ends represent inhibitory effects. Angiotensinogen, a precursor of angiotensin peptides, is the only known naturally occurring renin substrate. Ang I is processed by ACE or ACE2 to produce Ang II and Ang-(1–7), respectively. Alternatively, Ang I can be converted to Ang II through chymase. Ang-(1–7) can be generated from Ang I, via Ang-(1–9), a pathway that utilizes both ACE2 and ACE, or by neprilysin that hydrolyzes Ang I directly to Ang-(1–7). Ang II acts in cells through two classes of seven trans-membrane G protein-coupled receptors: the angiotensin type I (AT1) and angiotensin type II (AT2) receptors. Upon binding of Ang II to ATR1, a downstream intracellular cascade is induced that results in cell proliferation, fibrosis and hypoxia by generating reactive oxygen species and subsequently pro-inflammatory and pro-angiogenic signals. The AT1 receptor is overexpressed in neoplastic tissues, suggesting its involvement in carcinogenesis. The role of AT2 receptors in cancer remains controversial, although including pro-apoptotic and anti-proliferative effects. Ang-(1–7) binds to MasR and counteracts the resulting effects of Ang II/AT1 receptor activation, preventing tissue remodeling, improving vascular and cardiac function, and promoting the downregulation of cell proliferation, migration and metastasis. Hypoxia up-regulates Ang II, ACE, and AT1 receptor, while downregulating ACE2 and AT2 receptor. Local angiotensin II predominantly exists in the hypoxic regions of tumors, while these tumor cells produce Ang II by a chymase-dependent mechanism. Subsequently, the hypoxic tumor microenvironment induces the upregulation of the ACE/Ang II/AT1R axis, which is associated with the hallmarks of cancer, while it downregulates the ACE2/Ang-(1–7)/Mas receptor axis. ACE, angiotensin converting enzyme; ACE2, angiotensin converting enzyme 2; AMNA, aminopeptidase A; AMNN, aminopeptidase N; Ang, angiotensin; AT1R, angiotensin receptor 1; AT2R, angiotensin receptor 2; AT4R, angiotensin receptor 4; CAGE, chymostatin-sensitive angiotensin II-generating enzyme; COX-2, cyclooxygenase 2; EMT, epithelial-to-mesenchymal transition; HIF1α, hypoxia-inducible factor 1-alpha; MASR, Mas receptor; NADPH, hydro-nicotinamide adenine dinucleotide phosphate; TGFβ1, transforming growth factor beta 1; t-PA, tissue-plasminogen activator; VEGF, vascular endothelial growth factor.

Figure 2

Angiotensin-associated pathways associated with cell proliferation, invasion, and migration in lung tumor microenvironment. Membrane-bound and soluble ACE and ACE2 catalyze the production of angiotensin II or angiotensin (1,7), ligands that exert regulatory functions in tumor microenvironment cells. The effects of activating Ang II/AT1R, Ang II/AT2R and Ang (1,7)/MasR axes’ signaling has been mostly studied in tumor cells, including lung cancer cells. Overall, in contrast to the Ang II/AT1R that mediates several pathological events associated with activated RAS, the Ang (1,7)/MasR and Ang II/AT2R pathways are thought to antagonize many of the cellular actions of the Ang II-AT1R axis. In cancer cells, upon binding of Ang II to AT1R, a pleiotropic downstream signaling cascade is triggered, ultimately causing, either directly or indirectly, upregulation of cell proliferation, survival, motility, migration, invasion and EMT. Activated AT1R subunits stimulate PLCβ, that hydrolyses membrane lipids, activates PKC and mobilization of intracellular Ca²⁺, while free Gβ and Gγ subunits bind and gate ion channels. Activated Gαq/11 units also activate the JAK-SHP2/STAT pathway and receptor tyrosine kinase (RTK) transactivation. Activation of RTK, depicted in the figure as EGFR, occurs through second messenger’s stimulation of ADAM family and MMPs to cleave its ligands (in the figure EGF and TGFα) that bind and activate RTK. Alternatively, the AT1R-mediated activation of MMPs can follow a PLCβ/DAG/PKC/c-SRC signaling mechanism to elicit increased ligands for RTK. Subsequent signaling upon activation of EGFR is represented in the figure using dashed arrows. Other intracellular cascades mediated by Ang II/AT1R include the activation of CXCR4/SDF-1 signaling through FAK/RhoA/ROCK1-2/MLC increasing cell contraction, migratory potential and tumor invasion. The Ang (1,7)/MasR activation inhibits NFAT transcriptional regulation that reduces proliferation. Notably, this pathway blocks the NF-kB molecule formation thereby impacting EMT (including Snail1-mediated), invasion and survival. In addition, the inhibitory effect over ERK1/2 and NAPH oxidase signaling pathways significantly impact cell proliferation. The Ang II/AT2R pathway signals are mediated through protein phosphatases PTP1B, PTP and PP2A. The inhibition of CAV-1 phosphorylation stops the Rab5/Rac1/GTP migratory potential of malignant cells, thus suppressing invasion. Furthermore, AT2R-associated increase in PTP and PP2A exerts blocking effects in RTK-mediated signals of the RAS/RAF/MEK1-2/ERK1-2 pathway at the level of MERK1/2 and RAS molecules, reducing cell proliferation. Macrophages, endothelial cells and fibroblasts are important components of the tumor microenvironment and capable of generating and expressing RAS components. These cells, beyond their functional ligands and receptors that are altered in tumor microenvironment, and reflect the crosstalk between all cell constituents, also use the RAS signaling pathway (mostly AT1R, but also MasR in endothelial cells) to yield functional characteristics that ultimately may favor the cell itself and enhance tumor growth. BIRC5, surviving gene; BCL2, B-cell leukemia/lymphoma 2; BAD, BCL2 associated agonist of cell death; GADD45, Growth Arrest and DNA Damage 45; SREBP, Sterol regulatory element binding proteins; ROCK1/2, Rho-associated protein kinase 1/2; Rab5, Ras-related protein Rab-5; S6K, ribosomal S6 kinase; PTP, protein tyrosine phosphatase; PP2A, Protein phosphatase 2; 4E-BP1, Eukaryotic translation initiation factor 4E-binding protein 1; IKKB, Inhibitor of nuclear factor kappa-B kinase subunit beta; c-SRC, cellular Proto-oncogene tyrosine-protein kinase; SHP2, Src homology region 2 domain-containing phosphatase-2; PTP1B, Protein tyrosine phosphatase 1B; MLC, myosin light chain; CAV1, caveolin 1; IL1, interleukin 1; TNFA, tumor necrosis factor; Snail1, Zinc finger protein SNAI1; SNAI1, Snail Family Transcriptional Repressor 1; JAK, janus kinase; STAT, signal transduction and activator of transcription; GTP, guanosine triphosphate; EGF, epidermal growth factor; EGFR, epidermal growth factor receptor; CXCL1, The chemokine (C-X-C motif) ligand 1; IL8, interleukin 8; NF-kB, Nuclear Factor-kappa B; SDF1, stromal cell-derived factor 1; IL6, interleukin 6; HGF, hepatocyte growth factor; RAS, oncogene protein p21; FGF, fibroblast growth factor; FGFR, fibroblast growth factor receptor; Cas9, caspase 9; Cas3, caspase 3; ERK1/2, extracellular signal-regulated kinase; PI3K/Akt, phosphoinositide 3-kinase/protein kinase B; MEK1/2, mitogen activated protein kinase kinase; HIF1α, hypoxia inducible factor 1 alpha; NO, nitric oxide; RhoA, Ras homolog family member A; MAPK, mitogen activated protein kinase; mTOR, mammalian target of rapamycin; IP3, inositol trisphosphate; DAG, diacylglycerol; M2, macrophage polarized towards M2; ADAM17, Desintegrin and metalloproteinase domain-containing protein 17; p38/MAPK, protein 38/mitogen activated protein kinase; AT1R, angiotensin receptor 1; AT2R, angiotensin receptor 2; MasR, G-protein coupled Mas receptor; VEGF, vascular endothelial growth factor; NADPH, reduced form of nicotinamide adenine dinucleotide phosphate; mACE, membrane angiotensin converting enzyme; sACE, soluble angiotensin converting enzyme; mACE2, membrane angiotensin converting enzyme 2; sACE2, soluble angiotensin converting enzyme 2; TGFBR, transforming growth factor beta receptor; VEGFR2, vascular endothelial growth factor receptor 2; TGFα, transforming growth factor alpha; Ang (1,7), angiotensin 1,7; PLCβ, phospholipase C beta; FAK, Focal adhesion kinase; NFAT, nuclear factor of activated T cells.

Figure 3

Angiotensin-associated pathways involved on hypoxia and angiogenesis in lung tumor microenvironment. In cancer cells, upon binding of Ang II to AT1R, a pleiotropic downstream signaling cascade is triggered, ultimately causing, either directly or indirectly, upregulation of angiogenesis and metastasis. Activated AT1R subunits trigger potent oxidant signaling through NADPH complex, which is involved in angiogenesis. Activated Gαq/11 units also activate the JAK-SHP2/STAT pathway and receptor tyrosine kinase (RTK) transactivation. Subsequent signaling upon activation of EGFR is herein represented. Macrophages, endothelial cells and fibroblasts are important components of the tumor microenvironment and capable of generating and expressing RAS components. These cells, beyond their functional ligands and receptors that are altered in tumor microenvironment, and reflect the crosstalk between all cell constituents, also use the RAS signaling pathway (mostly AT1, but also MasR in endothelial cells) to yield functional characteristics that ultimately may favor the cell itself and enhancing tumor angiogenesis and metastasis. 4E-BP1, Eukaryotic translation initiation factor 4E-binding protein 1; IKKB, Inhibitor of nuclear factor kappa-B kinase subunit beta; c-SRC, cellular Proto-oncogene tyrosine-protein kinase; SHP2, Src homology region 2 domain-containing phosphatase-2; IL1, interleukin 1; JAK, janus kinase; STAT, signal transduction and activator of transcription; Ang I, angiotensin I; Ang II, angiotensin II; EGF, epidermal growth factor; EGFR, epidermal growth factor receptor; ANGPT2, angiopoietin 2; ICAM1, Intercellular Adhesion Molecule 1; VCAM1, vascular cell adhesion molecule 1; NF-kB, Nuclear Factor-kappa B; ROS, reactive oxygen species; ERK1/2, extracellular signal-regulated kinase; PLCγ/PKC, phospholipase C gamma/protein kinase C; PI3K/Akt, phosphoinositide 3-kinase/protein kinase B; MEK1/2, mitogen activated protein kinase kinase; HIF1α, hypoxia inducible factor 1 alpha; NO, nitric oxide; MAPK, mitogen activated protein kinase; mTOR, mammalian target of rapamycin; IP3, inositol trisphosphate; DAG, diacylglycerol; M2, macrophage polarized towards M2; ADAM17, Disintegrin and metalloproteinase domain-containing protein 17; AT1R, angiotensin receptor 1; AT2R, angiotensin receptor 2; MasR, G-protein coupled Mas receptor; VEGF, vascular endothelial growth factor; NADPH, reduced form of nicotinamide adenine dinucleotide phosphate; mACE, membrane angiotensin converting enzyme; sACE, soluble angiotensin converting enzyme; mACE2, membrane angiotensin converting enzyme 2; sACE2, soluble angiotensin converting enzyme 2; VEGFR1, vascular endothelial growth factor receptor 1; VEGFR2, vascular endothelial growth factor receptor 2 Ang (1,7), angiotensin 1,7; PLCβ, phospholipase C beta.

Figure 4

Angiotensin-associated immunoinflammatory pathways in lung tumor microenvironment. Extracellular proteins of the RAS, ligands (Ang I, Ang II and Ang 1,7) and enzymes (ACE, ACE2 and neprilysin), are represented with distinct colors in the tumor microenvironment. The expression and cleavage of ACE and ACE2 are represented in tumor and endothelial cells, showing the AT1R signaling-associated activation of ADAM17 that cleaves the ectodomain of mACE and mACE2 shedding the enzymes into sACE and sACE2. The Ang II/AT1R-mediated direct intracellular signaling is represented with full black arrows as a first step after AT1R triggering in the cascade. The subsequent steps of signaling cascades are depicted, up to moving towards intranuclear space, using dashed black arrows. Intranuclear signaling from these pathways mainly results in transcriptional regulatory effects and is represented by full white arrows. The Ang II/AT2R and Ang (1,7)/MasR-mediated counter-regulatory mechanisms are depicted using black arrows and when adequate the suppressive step is represented by blunt-ended red arrows. In cancer cells, upon binding of Ang II to AT1R, a pleiotropic downstream signaling cascade is triggered, ultimately causing, either directly or indirectly inflammation immune cells recruitment. Activated AT1R triggers potent oxidant signaling through NADPH complex, which is involved in inflammation and angiogenesis. Other intracellular cascades mediated by Ang II/AT1R include the activation of PLA2/AA/COX-2/PGE2 signaling. The Ang (1,7)/MasR activation elicits downstream signaling through PI3K/Akt/NOS3 or NOS1 to produce NO that inhibits NFAT transcriptional regulation that reduces inflammation. Notably, this pathway blocks the NF-kB molecule formation thereby impacting inflammation. In addition, the inhibitory effect over COX-2 significantly impact inflammation. Macrophages, endothelial cells and fibroblasts are important components of the tumor microenvironment and capable of generating and expressing RAS components. These cells, beyond their functional ligands and receptors that are altered in tumor microenvironment, and reflect the crosstalk between all cell constituents, also use the RAS signaling pathway (mostly AT1, but also MasR in endothelial cells) to yield functional characteristics that ultimately may favor the cell itself and enhance tumor growth and aggressiveness. PLA2, phospholipase A2; PTP, protein tyrosine phosphatase; PP2A, Protein phosphatase 2; IKKB, Inhibitor of nuclear factor kappa-B kinase subunit beta; CARMA3, CARD recruited membrane associated protein 3; MALT1, Mucosa-associated lymphoid tissue lymphoma translocation protein 1; BCL-10, B-cell lymphoma/leukemia 10; c-SRC, cellular Proto-oncogene tyrosine-protein kinase; SHP2, Src homology region 2 domain-containing phosphatase-2; AA, arachidonic acid; COX-2, cyclooxygenase 2; PGE2, prostaglandin E2; IL1, interleukin 1; TNFA, tumor necrosis factor; Ang I, angiotensin I; Ang II, angiotensin II; GTP, guanosine triphosphate; EGF, epidermal growth factor; EGFR, epidermal growth factor receptor; ANGPT2, angiopoietin 2; ICAM1, Intercellular Adhesion Molecule 1; VCAM1, vascular cell adhesion molecule 1; CXCL1, The chemokine (C-X-C motif) ligand 1; IL8, interleukin 8; NF-kB, Nuclear Factor-kappa B; NFKB1, Nuclear Factor-kappa B Subunit 1; IL6, interleukin 6; NFE2L2, Nuclear Factor, Erythroid 2 Like 2; HGF, hepatocyte growth factor; RAS, oncogene protein p21; ROS, reactive oxygen species; NOS3, nitric oxide synthase 3 endothelial; NOS1, nitric oxide synthase 1 neuronal; Cas9, caspase 9; Cas3, caspase 3; ERK1/2, extracellular signal-regulated kinase; PLCγ/PKC, phospholipase C gamma/protein kinase C; PI3K/Akt, phosphoinositide 3-kinase/protein kinase B; TNFR1, tumor necrosis factor receptor 1; c-Raf, kinase Raf-1; MEK1/2, mitogen activated protein kinase kinase; HIF1α, hypoxia inducible factor 1 alpha; NO, nitric oxide; RhoA, Ras homolog family member A; IP3, inositol trisphosphate; DAG, diacylglycerol; M2, macrophage polarized towards M2; ADAM17, Disintegrin and metalloproteinase domain-containing protein 17; p38/MAPK, protein 38/mitogen activated protein kinase; AT1R, angiotensin receptor 1; AT2R, angiotensin receptor 2; MASR, G-protein coupled Mas receptor; VEGFA, vascular endothelial growth factor A; NADPH, reduced form of nicotinamide adenine dinucleotide phosphate; mACE, membrane angiotensin converting enzyme; sACE, soluble angiotensin converting enzyme; mACE2, membrane angiotensin converting enzyme 2; sACE2, soluble angiotensin converting enzyme 2; PDGFRβ, platelet derived growth factor receptor beta; VEGFR1, vascular endothelial growth factor receptor 1; VEGFR2, vascular endothelial growth factor receptor 2; TGFα, transforming growth factor alpha; Ang (1,7), angiotensin 1,7; PLCβ, phospholipase C beta; FAK, Focal adhesion kinase; NFAT, nuclear factor of activated T cells; PDGF, platelet derived growth factor.