Macrophage-fibroblast JAK/STAT dependent crosstalk promotes liver metastatic outgrowth in pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) is a highly metastatic disease for which better therapies are urgently needed. Fibroblasts and macrophages are heterogeneous cell populations able to enhance metastasis, but the role of a macrophage-fibroblast crosstalk in regulating their pro-metastatic functions remains poorly understood. Here we deconvolve how macrophages regulate metastasis-associated fibroblast (MAF) heterogeneity in the liver. We identify three functionally distinct MAF populations, among which the generation of pro-metastatic and immunoregulatory myofibroblastic-MAFs (myMAFs) critically depends on macrophages. Mechanistically, myMAFs are induced through a STAT3-dependent mechanism driven by macrophage-derived progranulin and cancer cell-secreted leukaemia inhibitory factor (LIF). In a reciprocal manner, myMAF secreted osteopontin promotes an immunosuppressive macrophage phenotype resulting in the inhibition of cytotoxic T cell functions. Pharmacological blockade of STAT3 or myMAF-specific genetic depletion of STAT3 restores an anti-tumour immune response and reduces metastases. Our findings provide molecular insights into the complex macrophage-fibroblast interactions in tumours and reveal potential targets to inhibit PDAC liver metastasis.

Efferocytosis reprograms the tumor microenvironment to promote pancreatic cancer liver metastasis.

Pancreatic ductal adenocarcinoma is a highly metastatic disease and macrophages support liver metastases. Efferocytosis, or engulfment of apoptotic cells by macrophages, is an essential process in tissue homeostasis and wound healing, but its role in metastasis is less well understood. Here, we found that the colonization of the hepatic metastatic site is accompanied by low-grade tissue injury and that efferocytosis-mediated clearance of parenchymal dead cells promotes macrophage reprogramming and liver metastasis. Mechanistically, progranulin expression in macrophages is necessary for efficient efferocytosis by controlling lysosomal acidification via cystic fibrosis transmembrane conductance regulator and the degradation of lysosomal cargo, resulting in LXRα/RXRα-mediated macrophage conversion and upregulation of arginase 1. Pharmacological blockade of efferocytosis or macrophage-specific genetic depletion of progranulin impairs macrophage conversion, improves CD8+ T cell functions, and reduces liver metastasis. Our findings reveal how hard-wired functions of macrophages in tissue repair contribute to liver metastasis and identify potential targets for prevention of pancreatic ductal adenocarcinoma liver metastasis.

Mesothelin Secretion by Pancreatic Cancer Cells Co-opts Macrophages and Promotes Metastasis.

Pancreatic ductal adenocarcinoma (PDAC) is a highly metastatic disease, yet effective treatments to inhibit PDAC metastasis are lacking. The rich PDAC tumor microenvironment plays a major role in disease progression. Macrophages are the most abundant immune cell population in PDAC tumors and can acquire a range of functions that either hinder or promote tumor growth and metastasis. Here, we identified that mesothelin secretion by pancreatic cancer cells co-opts macrophages to support tumor growth and metastasis of cancer cells to the lungs, liver, and lymph nodes. Mechanistically, secretion of high levels of mesothelin by metastatic cancer cells induced the expression of VEGF alpha (VEGFA) and S100A9 in macrophages. Macrophage-derived VEGFA fed back to cancer cells to support tumor growth, and S100A9 increased neutrophil lung infiltration and formation of neutrophil extracellular traps. These results reveal a role for mesothelin in regulating macrophage functions and interaction with neutrophils to support PDAC metastasis. SIGNIFICANCE: Mesothelin secretion by cancer cells supports pancreatic cancer metastasis by inducing macrophage secretion of VEGFA and S100A9 to support cancer cell proliferation and survival, recruit neutrophils, and stimulate neutrophil extracellular trap formation. See related commentary by Alewine, p. 513.

Chemotherapy-induced infiltration of neutrophils promotes pancreatic cancer metastasis via Gas6/AXL signalling axis.

OBJECTIVE: Pancreatic ductal adenocarcinoma (PDAC) is a highly metastatic disease and cytotoxic chemotherapy is the standard of care treatment for patients with advanced disease. Here, we investigate how the microenvironment in PDAC liver metastases reacts to chemotherapy and its role in metastatic disease progression post-treatment, an area which is poorly understood. DESIGN: The impact of chemotherapy on metastatic disease progression and immune cell infiltrates was characterised using flow and mass cytometry combined with transcriptional and histopathological analysis in experimental PDAC liver metastases mouse models. Findings were validated in patient derived liver metastases and in an autochthonous PDAC mouse model. Human and murine primary cell cocultures and ex vivo patient-derived liver explants were deployed to gain mechanistical insights on whether and how chemotherapy affects the metastatic tumour microenvironment. RESULTS: We show that in vivo, chemotherapy induces an initial infiltration of proinflammatory macrophages into the liver and activates cytotoxic T cells, leading only to a temporary restraining of metastatic disease progression. However, after stopping treatment, neutrophils are recruited to the metastatic liver via CXCL1 and 2 secretion by metastatic tumour cells. These neutrophils express growth arrest specific 6 (Gas6) which leads to AXL receptor activation on tumour cells enabling their regrowth. Disruption of neutrophil infiltration or inhibition of the Gas6/AXL signalling axis in combination with chemotherapy inhibits metastatic growth. Chemotherapy increases Gas6 expression in circulating neutrophils from patients with metastatic pancreatic cancer and recombinant Gas6 is sufficient to promote tumour cell proliferation ex vivo, in patient-derived metastatic liver explants. CONCLUSION: Combining chemotherapy with Gas6/AXL or neutrophil targeted therapy could provide a therapeutic benefit for patients with metastatic pancreatic cancer.

Transient protein accumulation at the center of the T cell antigen-presenting cell interface drives efficient IL-2 secretion.

Supramolecular signaling assemblies are of interest for their unique signaling properties. A µm scale signaling assembly, the central supramolecular signaling cluster (cSMAC), forms at the center of the interface of T cells activated by antigen-presenting cells. We have determined that it is composed of multiple complexes of a supramolecular volume of up to 0.5 µm3 and associated with extensive membrane undulations. To determine cSMAC function, we have systematically manipulated the localization of three adaptor proteins, LAT, SLP-76, and Grb2. cSMAC localization varied between the adaptors and was diminished upon blockade of the costimulatory receptor CD28 and deficiency of the signal amplifying kinase Itk. Reconstitution of cSMAC localization restored IL-2 secretion which is a key T cell effector function as dependent on reconstitution dynamics. Our data suggest that the cSMAC enhances early signaling by facilitating signaling interactions and attenuates signaling thereafter through sequestration of a more limited set of signaling intermediates.

Cells receive dozens of signals at different times and in different places. Integrating incoming information and deciding how to respond is no easy task. Signaling molecules on the cell surface pass messages inwards using chemical messengers that interact in complicated networks within the cell. One way to unravel the complexity of these networks is to look at specific groups of signaling molecules in test tubes to see how they interact. But the interior of a living cell is a very different environment. Molecules inside cells are tightly packed and, under certain conditions, they interact with each other by the thousands. They form structures known as 'supramolecular complexes', which changes their behavior. One such supramolecular complex is the 'central supramolecular activation cluster', or cSMAC for short. It forms under the surface of immune cells called T cells when they are getting ready to fight an infection. Under the microscope, the cSMAC looks like the bullseye of a dartboard, forming a crowd of signaling molecules at the center of the interface between the T cell and another cell. Its exact role is not clear, but evidence suggests it helps to start and stop the signals that switch T cells on. The cSMAC contains two key protein adaptors called LAT and SLP-76 that help to hold the structure together. So, to find out what the cSMAC does, Clark et al. genetically modified these adaptors to gain control over when the cSMAC forms. Clark et al. examined mouse T cells using super-resolution microscopy and electron microscopy, watching as other immune cells delivered the signal to switch on. As the T cells started to activate, the composition of the cSMAC changed. In the first two minutes after the cells started activating, the cSMAC included a large number of different components. This made T cell activation more efficient, possibly because the supramolecular complex was helping the network of signals to interact. Later, the cSMAC started to lose many of these components. Separating components may have helped to stop the activation signals. Understanding how T cells activate could lead to the possibility of turning them on or off in immune-related diseases. But these findings are not just relevant to immune cells. Other cells also use supramolecular complexes to control their signaling. Investigating how these complexes change over time could help us to understand how other cell types make decisions.