Macrophage | EPFL Graph Search

Macrophages (abbreviated as Mφ, MΦ or MP) (large eaters, from Greek μακρός (makrós) = large, φαγεῖν (phagein) = to eat) are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris, and foreign substances, which do not have proteins that are specific to healthy body cells on their surface. This process is called phagocytosis, which acts to defend the host against infection and injury. Macrophages are found in essentially all tissues, where they patrol for potential pathogens by amoeboid movement. They take various forms (with various names) throughout the body (e.g., histiocytes, Kupffer cells, alveolar macrophages, microglia, and others), but all are part of the mononuclear phagocyte system. Besides phagocytosis, they play a critical role in nonspecific defense (innate immunity) and also help initiate specific defense mechanisms (adaptive immunity) by recruiting other immune cells such as lymphocytes. For

Immunosuppressive roles of Activin-A in melanoma and characterization of its precursor cleavage

Katarina Pinjusic

Activin-A, a transforming growth factor êµ family member, is a pleiotropic cytokine with diverse functions in development, fertility, adult tissue homeostasis, and aging. Accordingly, deregulation of Activin-A signaling has been associated with many pathological conditions, including cancer and cancer-associated muscle wasting (cachexia). Activin-A was shown to signal in endocrine, but also local autocrine and paracrine manner. Its secretion in many cancer types is associated with a poor prognosis. Previous studies suggest that Activin-A expression in melanoma promotes tumor growth and metastasis indirectly by inhibiting adaptive anti-tumor immunity, leading to a decrease in the intratumoral frequency of cytotoxic CD8+ T cells (CTLs). However, the underlying mechanisms and the relevant direct target cells of Activin-A and their significance for cancer therapies remained unknown. Similar to other TGFêµ-related ligands, proActivin-A is cleaved by proprotein convertases (PCs) to release mature ligands. However, unlike other family members whose signaling is tightly regulated, Activin-A apparently does not have latency.In this thesis, I characterize proActivin-A cleavage and show that one prodomain can be cleaved independently of known PCs. The resulting hemi-cleaved Activin-A can bind activin type II receptors and induce SMAD3 signaling in reporter cells. A protein interactome screen and analysis of cleavage intermediates in plasma revealed that the hemi-cleaved Activin-A likely interacts with extracellular matrix proteins via the remaining prodomain where it promotes local signaling and regulates trafficking. Luciferase reporter assay showed that hemi-cleaved Activin-A can avoid, at least partially, inhibition by endogenous inhibitors FSTL3 and FST, and enable parallel activation of BMP and Activin signaling pathways. Finally, analysis of B16-F1 melanoma models revealed that only fully cleaved Activin-A in source cells increased tumor growth by acting locally in the tumor microenvironment suggesting that the context of Activin-A precursor processing regulates its tumor growth-promoting effect.The second part of this thesis addresses the mechanisms of Activin-induced immunosuppression in melanoma. We found that Activin-A impairs CTL function indirectly and independently of CD4+ T cell, CSF1R+ macrophages, and IL4 signaling. At least in part, anti-tumor CTL responses are impaired by the inhibitory effects of Activin-A on the secretion of critical CTL-recruiting chemokines CXCL9 and CXCL10 by macrophages and dendritic cells (DCs). Furthermore, Activin-A conferred resistance to immune checkpoint blockade therapy. Characterization of Activin-induced changes in the gene expression of tumor-infiltrating cells by Single cell RNA sequencing revealed that INHBA expression induced the most changes in DCs and least in T cells. Interestingly, the most prominently induced hallmark in Activin-secreting tumors across cell types was the IFN signature. In vitro analyses showed that Activin-A increases IFNÎ³-induced activation of STAT1 and confers resistance to cytostatic IFN signaling in cancer cells.Altogether, the findings of this thesis expand our knowledge on the regulation of Activin-A signaling by precursor cleavage and offer insights into mechanisms of Activin-induced immunosuppression in melanoma. Inhibition of Activin-A maturation thus emerges as a potential new strategy to improve responses to immunotherapies in melanoma and likely other cancers

EPFL2022

Functional characterization of the virulence determinant ESX-1 from Mycobacterium tuberculosis

Paloma Julia Soler Arnedo

Tuberculosis (TB) is a chronic infectious disease that mainly affects the lungs and causes extensive human morbidity and mortality. It results from infection with Mycobacterium tuberculosis, a slow-growing intracellular pathogen that can replicate and survive inside macrophages. M. tuberculosis relies on the specialised ESX-1 secretion system to export virulence factors needed for intracellular spread and pathogenesis. The ESX-1 apparatus is a multi-subunit nanomachine composed of ~20 polypeptides including membrane proteins, ATPases, proteases, chaperones and substrates. Although many of the individual components of this secretion system have been characterised, the overall mechanism underlying ESX-1 secretion is still far from clear. To obtain a more comprehensive picture of the functioning of the ESX-1 apparatus, we have studied various components which were largely unexplored in M. tuberculosis. The structural component EccE1, the ESX-1 specific protein EspL and the transcriptional regulator WhiB6 have been investigated in this thesis using an integrative approach involving genetics, biochemistry, proteomics and microscopy. We have demonstrated that EccE1 is a membrane- and cell-wall associated protein critical for secretion of ESX-1 substrates and M. tuberculosis-mediated cell lysis. Deletion of eccE1 from the chromosome severely compromised secretion of EsxA, EsxB, EspA and EspC but not EspB. Localization studies using a florescent-fusion protein showed that EccE1 localises to the poles of M. tuberculosis in the presence of an active ESX-1 system. Our study also shows that EspL is a cytosolic protein needed for stabilising EspE, EspF and EspH, suggesting that it acts as a specific chaperone of the ESX-1 secretion system. Moreover, EspL was shown to interact with EspD and to be important for the secretion of ESX-1 substrates. Lack of EspL resulted in a growth defect ex vivo, loss of cytotoxicity and reduction of innate cytokine production demonstrating its critical role in M. tuberculosis virulence. Analysis of the transcriptional response revealed that the only gene deregulated in the absence of espL was whiB6, encoding a transcriptional factor that positively controls ESX-1 genes. To explore the role of this regulator in M. tuberculosis virulence, we generated a deletion mutant of whiB6 and discovered that its loss resulted in severe reduction of cytotoxicity ex vivo. Overall this investigation improves our current understanding of the ESX-1 secretion system and of the molecular basis of M. tuberculosis virulence. The increased knowledge of the complex interactions between the pathogen and the human host will hopefully translate into new strategies to control the spread of TB.

EPFL2018

Regulation of macrophage arginase expression and tumor growth by the Ron receptor tyrosine kinase

Michele De Palma, Mario Leonardo Squadrito, Shan Yu

M1 activation of macrophages promotes inflammation and immunity to intracellular pathogens, whereas M2 macrophage activation promotes resolution of inflammation, wound healing, and tumor growth. These divergent phenotypes are characterized, in part, by the expression of inducible NO synthase and arginase I (Arg1) in M1 versus M2 activated macrophages, respectively. In this study, we demonstrate that the Ron receptor tyrosine kinase tips the balance of macrophage activation by attenuating the M1 phenotype while promoting expression of Arg1 through a Stat6-independent mechanism. Induction of the Arg1 promoter by Ron is mediated by an AP-1 site located 433 bp upstream of the transcription start site. Treatment of primary macrophages with macrophage stimulating protein, the ligand for Ron, induces potent MAPK activation, upregulates Fos, and enhances binding of Fos to the AP-1 site in the Arg1 promoter. In vivo, Arg1 expression in tumor-associated macrophages (TAMs) from Ron(-/-) mice was significantly reduced compared with that in TAMs from control animals. Furthermore, we show that Ron is expressed specifically by Tie2-expressing macrophages, a TAM subset that exhibits a markedly skewed M2 and protumoral phenotype. Decreased Arg1 in TAMs from Ron(-/-) mice was associated with reduced syngeneic tumor growth in these animals. These findings indicate that Ron induces Arg1 expression in macrophages through a previously uncharacterized AP-1 site in the Arg1 promoter and that Ron could be therapeutically targeted in the tumor microenvironment to inhibit tumor growth by targeting expression of Arg1.