Small extracellular vesicle-mediated bidirectional crosstalk between neutrophils and tumor cells

Abstract

Neutrophils are the first line of defense against tissue injury and play an important role in tumor progression. Tumor-associated neutrophils (TANs) mediate pro-tumor immunosuppressive activity and their infiltration into tumors is associated with poor outcome in a variety of malignant diseases. The tumor cell-neutrophil crosstalk is mediated by small extracellular vesicles (sEVs) also referred to as exosomes which represent a major mechanism for intercellular communication. This review will address the role of neutrophil-derived sEVs (NEX) in reprogramming the TME and on mechanisms that regulate the dual potential of NEX to promote tumor progression on one hand and suppress tumor growth on the other. Emerging data suggest that both, NEX and tumor-derived sEVs (TEX) carry complex molecular cargos which upon delivery to recipient cells in the tumor microenvironment (TME) modulate their behavior and reprogram them to mediate pro-inflammatory or immunosuppressive responses. Although it remains unknown how the balance between the often conflicting signaling of TEX and NEX is regulated, this review is an attempt to provide insights into mechanisms that underpin this complex bidirectional crosstalk. A better understanding of the signals NEX process or deliver in the TME might lead to the development of novel approaches to the control of tumor progression in the future.

Keywords: Neutrophils; Small extracellular vesicles; Tumor microenvironment (TME); Tumor-associated neutrophils (TAN); Tumor-derived exosomes (TEX).

Figure 1.

Neutrophil mobilization and functions in cancer. (A) Cells in the TME release cytokines, such as G-CSF, which induces granulopoiesis in the bone marrow, and chemokines which stimulate the migration of different neutrophil subpopulations. Some factors, such as TGF-β, are involved in promoting a pro-tumor phenotype in neutrophils. (B) Granulopoiesis is the formation and maturation of neutrophils, which is also important for granule production. Neutrophils are attracted to the bloodstream through cytokines and chemokines, especially by the release of IL-8 and their activation via CXCR2. Neutrophil primes with the first stimuli and enhanced expression of adhesion molecules, which allows diapedesis. When neutrophils reach the tumor site, they are exposed to second stimuli, such as DAMPs, and accomplish their major functions: NETosis, degranulation and extracellular vesicle release. Abbreviations: G-CSF - granulocyte colony-stimulating factor, IFNγ – interferon gamma, TGF-β - transforming growth factor beta, IL-8 - interleukin-8, CXCR2 - CXC chemokine receptor 2, DAMPs - damage-associated molecular patterns, PMN - polymorphonuclear, MPO - myeloperoxidase, NE – neutrophil elastase, MMP-9 – metalloproteinase 9, NGAL – neutrophil gelatinase-associated lipocalin

Figure 2:

The role neutrophils in the tumor microenvironment. (A) The composition of the TME is complex and includes, in addition to tumor cells, surrounding blood vessels, the ECM, and non-malignant cells. (B) Tumor cells are capable of producing sEVs as a mean of cell communication. The biogenesis of these sEVs occurs via initial endocytosis, which forms early endosomes and later MVBs with ILVs, followed by exocytosis and sEV release. sEVs can be internalized by recipient cells and reprogram its phenotype and functions. Neutrophils can internalize sEVs via endocytosis. Also, neutrophils are capable of producing their own sEVs (NEX), which are released to the extracellular space and interact with a variety of different cells types. (C) General cargo composition of sEVs: the cargo changes according to the metabolism of the parent cell and each sEV can carry different molecules even if derived from the same cell. (D) Neutrophils express a variety of cell surface proteins: chemokine receptors, for responding to chemokines; toll-like receptors, which recognize tumor molecules, such as HMGB1; adhesion molecules for migration and diapedesis; activation markers; adenosine receptors, which bind ADO and enhance immunosuppressive functions. Abbreviations: TME - tumor microenvironment, ECM - extracellular matrix, HMGB1 - high mobility group box 1, ADO – adenosine,

Figure 3.

Differential neutrophil polarization as source of N1 and N2 NEX. The phenotypes and biological functions of neutrophils are heterogenous and it is most likely that this heterogeneity is reflected in NEX. The molecular content of NEX was found to be varying depending on the microenvironmental conditions of the parent cells, thus N1 and N2 neutrophils might produce N1 NEX and N2 NEX, respectively. N1 NEX have the potential to promote anti-tumor effects and might enhance the anti-tumor immune response with special regards to lymphocytes. N2 NEX carry tumor-promoting cargo components, which are potentially involved in promoting tumor growth, survival, angiogenesis and escape of immune surveillance. Abbreviations: NEX – neutrophil-derived small extracellular vesicles, A2MG – alpha-2-macroglobulin, MPO - myeloperoxidase, NE – neutrophil elastase, MMP-2 – mettaloproteinase-2, FGF1 - fibroblast growth factor 1, MMP-9 – mettaloproteinase-9, HSPs - heat shock proteins, IL-6 – interleukin-6, LTB4 - leukotriene B4, 5-LO - 5-lipoxygenase, FLAP - 5-lipoxygenase-activating protein, LTA4H - leukotriene A4 Hydrolase, VEGF - vascular endothelial growth factor

Figure 4.

Tumor cells release TEX which interact with a variety of cell types, including TANs in the TME and neutrophils at distant sites. TEX were shown to alter the phenotype and functional behavior of neutrophils. This figure summarizes the tumor-promoting effects of neutrophils reprogrammed by the tumor. Abbreviations: TEX – tumor-derived small extracellular vesicles, TANs – tumor-associated neutrophils, TME – tumor microenvironment, MMP-9 – mettaproteinase-9, VEGF - vascular endothelial growth factor , PD1 - programmed cell death protein 1, PDL1 - programmed cell death ligand 1, IL – interleukin