Correction: Zwergel et al. Novel Quinoline Compounds Active in Cancer Cells through Coupled DNA Methyltransferase Inhibition and Degradation. Cancers 2020, 12, 447.

In the original publication [...].

Mechanisms of mesothelial cell response to viral infections: HDAC1-3 inhibition blocks poly(I:C)-induced type I interferon response and modulates the mesenchymal/inflammatory phenotype.

Infectious peritonitis is a leading cause of peritoneal functional impairment and a primary factor for therapy discontinuation in peritoneal dialysis (PD) patients. Although bacterial infections are a common cause of peritonitis episodes, emerging evidence suggests a role for viral pathogens. Toll-like receptors (TLRs) specifically recognize conserved pathogen-associated molecular patterns (PAMPs) from bacteria, viruses, and fungi, thereby orchestrating the ensuing inflammatory/immune responses. Among TLRs, TLR3 recognizes viral dsRNA and triggers antiviral response cascades upon activation. Epigenetic regulation, mediated by histone deacetylase (HDAC), has been demonstrated to control several cellular functions in response to various extracellular stimuli. Employing epigenetic target modulators, such as epidrugs, is a current therapeutic option in several cancers and holds promise in treating viral diseases. This study aims to elucidate the impact of TLR3 stimulation on the plasticity of human mesothelial cells (MCs) in PD patients and to investigate the effects of HDAC1-3 inhibition. Treatment of MCs from PD patients with the TLR3 agonist polyinosinic:polycytidylic acid (Poly(I:C)), led to the acquisition of a bona fide mesothelial-to-mesenchymal transition (MMT) characterized by the upregulation of mesenchymal genes and loss of epithelial-like features. Moreover, Poly(I:C) modulated the expression of several inflammatory cytokines and chemokines. A quantitative proteomic analysis of MCs treated with MS-275, an HDAC1-3 inhibitor, unveiled altered expression of several proteins, including inflammatory cytokines/chemokines and interferon-stimulated genes (ISGs). Treatment with MS-275 facilitated MMT reversal and inhibited the interferon signature, which was associated with reduced STAT1 phosphorylation. However, the modulation of inflammatory cytokine/chemokine production was not univocal, as IL-6 and CXCL8 were augmented while TNF-α and CXCL10 were decreased. Collectively, our findings underline the significance of viral infections in acquiring a mesenchymal-like phenotype by MCs and the potential consequences of virus-associated peritonitis episodes for PD patients. The observed promotion of MMT reversal and interferon response inhibition by an HDAC1-3 inhibitor, albeit without a general impact on inflammatory cytokine production, has translational implications deserving further analysis.

Immune checkpoints between epithelial-mesenchymal transition and autophagy: A conflicting triangle.

Inhibitory immune checkpoint (ICP) molecules are pivotal in inhibiting innate and acquired antitumor immune responses, a mechanism frequently exploited by cancer cells to evade host immunity. These evasion strategies contribute to the complexity of cancer progression and therapeutic resistance. For this reason, ICP molecules have become targets for antitumor drugs, particularly monoclonal antibodies, collectively referred to as immune checkpoint inhibitors (ICI), that counteract such cancer-associated immune suppression and restore antitumor immune responses. Over the last decade, however, it has become clear that tumor cell-associated ICPs can also induce tumor cell-intrinsic effects, in particular epithelial-mesenchymal transition (EMT) and macroautophagy (hereafter autophagy). Both of these processes have profound implications for cancer metastasis and drug responsiveness. This article reviews the positive or negative cross-talk that tumor cell-associated ICPs undergo with autophagy and EMT. We discuss that tumor cell-associated ICPs are upregulated in response to the same stimuli that induce EMT. Moreover, ICPs themselves, when overexpressed, become an EMT-inducing stimulus. As regards the cross-talk with autophagy, ICPs have been shown to either stimulate or inhibit autophagy, while autophagy itself can either up- or downregulate the expression of ICPs. This dynamic equilibrium also extends to the autophagy-apoptosis axis, further emphasizing the complexities of cellular responses. Eventually, we delve into the intricate balance between autophagy and apoptosis, elucidating its role in the broader interplay of cellular dynamics influenced by ICPs. In the final part of this article, we speculate about the driving forces underlying the contradictory outcomes of the reciprocal, inhibitory, or stimulatory effects between ICPs, EMT, and autophagy. A conclusive identification of these driving forces may allow to achieve improved antitumor effects when using combinations of ICIs and compounds acting on EMT and/or autophagy. Prospectively, this may translate into increased and/or broadened therapeutic efficacy compared to what is currently achieved with ICI-based clinical protocols.

Contribution of Autophagy to Epithelial Mesenchymal Transition Induction during Cancer Progression.

Epithelial Mesenchymal Transition (EMT) is a dedifferentiation process implicated in many physio-pathological conditions including tumor transformation. EMT is regulated by several extracellular mediators and under certain conditions it can be reversible. Autophagy is a conserved catabolic process in which intracellular components such as protein/DNA aggregates and abnormal organelles are degraded in specific lysosomes. In cancer, autophagy plays a controversial role, acting in different conditions as both a tumor suppressor and a tumor-promoting mechanism. Experimental evidence shows that deep interrelations exist between EMT and autophagy-related pathways. Although this interplay has already been analyzed in previous studies, understanding mechanisms and the translational implications of autophagy/EMT need further study. The role of autophagy in EMT is not limited to morphological changes, but activation of autophagy could be important to DNA repair/damage system, cell adhesion molecules, and cell proliferation and differentiation processes. Based on this, both autophagy and EMT and related pathways are now considered as targets for cancer therapy. In this review article, the contribution of autophagy to EMT and progression of cancer is discussed. This article also describes the multiple connections between EMT and autophagy and their implication in cancer treatment.

HDAC1/2 control mesothelium/ovarian cancer adhesive interactions impacting on Talin-1-α5ß1-integrin-mediated actin cytoskeleton and extracellular matrix protein remodeling.

BACKGROUND: Peritoneal metastasis, which accounts for 85% of all epithelial ovarian carcinoma (EOC) metastases, is a multistep process that requires the establishment of adhesive interactions between cancer cells and the peritoneal membrane. Interrelations between EOC and the mesothelial stroma are critical to facilitate the metastatic process. No data is available so far on the impact of histone acetylation/deacetylation, a potentially relevant mechanism governing EOC metastasis, on mesothelial cells (MCs)-mediated adhesion. METHODS: Static adhesion and peritoneal clearance experiments were performed pretreating mesenchymal-like MCs and platinum-sensitive/resistant EOC cell lines with MS-275-a Histone deacetylase (HDAC)1-3 pharmacological inhibitor currently used in combination trials. Results were acquired by confocal microscopy and were analyzed with an automated Opera software. The role of HDAC1/2 was validated by genetic silencing. The role of α4-, α5-α1 Integrins and Fibronectin-1 was validated using specific monoclonal antibodies. Quantitative proteomic analysis was performed on primary MCs pretreated with MS-275. Decellularized matrices were generated from either MS-275-exposed or untreated cells to study Fibronectin-1 extracellular secretion. The effect of MS-275 on ß1 integrin activity was assessed using specific monoclonal antibodies. The role of Talin-1 in MCs/EOC adhesion was analyzed by genetic silencing. Talin-1 ectopic expression was validated as a rescue tool from MS-275-induced phenotype. The in vivo effect of MS-275-induced MC remodeling was validated in a mouse model of peritoneal EOC dissemination. RESULTS: Treatment of MCs with non-cytotoxic concentrations of MS-275 caused a consistent reduction of EOC adhesion. Proteomic analysis revealed several pathways altered upon MC treatment with MS-275, including ECM deposition/remodeling, adhesion receptors and actin cytoskeleton regulators. HDAC1/2 inhibition hampered actin cytoskeleton polymerization by downregulating actin regulators including Talin-1, impairing ß1 integrin activation, and leading to abnormal extracellular secretion and distribution of Fibronectin-1. Talin-1 ectopic expression rescued EOC adhesion to MS-275-treated MCs. In an experimental mouse model of metastatic EOC, MS-275 limited tumor invasion, Fibronectin-1 secretion and the sub-mesothelial accumulation of MC-derived carcinoma-associated fibroblasts. CONCLUSION: Our study unveils a direct impact of HDAC-1/2 in the regulation of MC/EOC adhesion and highlights the regulation of MC plasticity by epigenetic inhibition as a potential target for therapeutic intervention in EOC peritoneal metastasis.

Metal-based nanoparticles in cancer therapy: Exploring photodynamic therapy and its interplay with regulated cell death pathways.

Photodynamic therapy (PDT) represents a non-invasive treatment strategy currently utilized in the clinical management of selected cancers and infections. This technique is predicated on the administration of a photosensitizer (PS) and subsequent irradiation with light of specific wavelengths, thereby generating reactive oxygen species (ROS) within targeted cells. The cellular effects of PDT are dependent on both the localization of the PS and the severity of ROS challenge, potentially leading to the stimulation of various cell death modalities. For many years, the concept of regulated cell death (RCD) triggered by photodynamic reactions predominantly encompassed apoptosis, necrosis, and autophagy. However, in recent decades, further explorations have unveiled additional cell death modalities, such as necroptosis, ferroptosis, cuproptosis, pyroptosis, parthanatos, and immunogenic cell death (ICD), which helps to achieve tumor cell elimination. Recently, nanoparticles (NPs) have demonstrated substantial advantages over traditional PSs and become important components of PDT, due to their improved physicochemical properties, such as enhanced solubility and superior specificity for targeted cells. This review aims to summarize recent advancements in the applications of different metal-based NPs as PSs or delivery systems for optimized PDT in cancer treatment. Furthermore, it mechanistically highlights the contribution of RCD pathways during PDT with metal NPs and how these forms of cell death can improve specific PDT regimens in cancer therapy.

BET Protein Inhibitor JQ1 Ameliorates Experimental Peritoneal Damage by Inhibition of Inflammation and Oxidative Stress.

Peritoneal dialysis (PD) is a current replacement therapy for end-stage kidney diseases (ESKDs). However, long-term exposure to PD fluids may lead to damage of the peritoneal membrane (PM) through mechanisms involving the activation of the inflammatory response and mesothelial-to-mesenchymal transition (MMT), leading to filtration failure. Peritoneal damage depends on a complex interaction among external stimuli, intrinsic properties of the PM, and subsequent activities of the local innate-adaptive immune system. Epigenetic drugs targeting bromodomain and extra-terminal domain (BET) proteins have shown beneficial effects on different experimental preclinical diseases, mainly by inhibiting proliferative and inflammatory responses. However the effect of BET inhibition on peritoneal damage has not been studied. To this aim, we have evaluated the effects of treatment with the BET inhibitor JQ1 in a mouse model of peritoneal damage induced by chlorhexidine gluconate (CHX). We found that JQ1 ameliorated the CHX-induced PM thickness and inflammatory cell infiltration. Moreover, JQ1 decreased gene overexpression of proinflammatory and profibrotic markers, together with an inhibition of the nuclear factor-κB (NF-κB) pathway. Additionally, JQ1 blocked the activation of nuclear factor erythroid 2-related factor 2 (NRF2) and restored changes in the mRNA expression levels of NADPH oxidases (NOX1 and NOX4) and NRF2/target antioxidant response genes. To corroborate the in vivo findings, we evaluated the effects of the BET inhibitor JQ1 on PD patients' effluent-derived primary mesothelial cells and on the MeT-5A cell line. JQ1 inhibited tumor necrosis factor-α (TNF-α)-induced proinflammatory gene upregulation and restored MMT phenotype changes, together with the downmodulation of oxidative stress. Taken together, these results suggest that BET inhibitors may be a potential therapeutic option to ameliorate peritoneal damage.

Novel Aspects of the Immune Response Involved in the Peritoneal Damage in Chronic Kidney Disease Patients under Dialysis.

Chronic kidney disease (CKD) incidence is growing worldwide, with a significant percentage of CKD patients reaching end-stage renal disease (ESRD) and requiring kidney replacement therapies (KRT). Peritoneal dialysis (PD) is a convenient KRT presenting benefices as home therapy. In PD patients, the peritoneum is chronically exposed to PD fluids containing supraphysiologic concentrations of glucose or other osmotic agents, leading to the activation of cellular and molecular processes of damage, including inflammation and fibrosis. Importantly, peritonitis episodes enhance peritoneum inflammation status and accelerate peritoneal injury. Here, we review the role of immune cells in the damage of the peritoneal membrane (PM) by repeated exposure to PD fluids during KRT as well as by bacterial or viral infections. We also discuss the anti-inflammatory properties of current clinical treatments of CKD patients in KRT and their potential effect on preserving PM integrity. Finally, given the current importance of coronavirus disease 2019 (COVID-19) disease, we also analyze here the implications of this disease in CKD and KRT.

Nanomedicine for autophagy modulation in cancer therapy: a clinical perspective.

In recent years, progress in nanotechnology provided new tools to treat cancer more effectively. Advances in biomaterials tailored for drug delivery have the potential to overcome the limited selectivity and side effects frequently associated with traditional therapeutic agents. While autophagy is pivotal in determining cell fate and adaptation to different challenges, and despite the fact that it is frequently dysregulated in cancer, antitumor therapeutic strategies leveraging on or targeting this process are scarce. This is due to many reasons, including the very contextual effects of autophagy in cancer, low bioavailability and non-targeted delivery of existing autophagy modulatory compounds. Conjugating the versatile characteristics of nanoparticles with autophagy modulators may render these drugs safer and more effective for cancer treatment. Here, we review current standing questions on the biology of autophagy in tumor progression, and precursory studies and the state-of-the-art in harnessing nanomaterials science to enhance the specificity and therapeutic potential of autophagy modulators.

Novel pyridine-containing histone deacetylase inhibitors strongly arrest proliferation, induce apoptosis and modulate miRNAs in cancer cells.

After over 30 years of research, the development of HDAC inhibitors led to five FDA/Chinese FDA-approved drugs and many others under clinical or preclinical investigation to treat cancer and non-cancer diseases. Herein, based on our recent development of pyridine-based isomers as HDAC inhibitors, we report a series of novel 5-acylamino-2-pyridylacrylic- and -picolinic hydroxamates and 2'-aminoanilides 5-8 as anticancer agents. The hydroxamate 5d proved to be quite HDAC3/6-selective exhibiting IC50 values of 80 and 11 nM, respectively, whereas the congener 5e behaved as inhibitor of HDAC1-3, -6, -8, and -10 (class I/IIb-selective inhibitor) at nanomolar level. Compound 5e provided a huge antiproliferative activity (nanomolar IC50 values) against both haematological and solid cancer cell lines. In leukaemia U937 cells, the hydroxamate 5d and the 2'-aminoanilide 8f induced remarkable cell death after 48 h, with 76% and 100% pre-G1 phase arrest, respectively, showing a stronger effect with respect to SAHA and MS-275 used as reference compounds. In U937 cells, the highest dose- and time-dependent cytodifferentiation was obtained by the 2'-aminoanilide 8d (up to 35% of CD11c positive/propidium iodide negative cells at 5 µM for 48 h). The same 8d and the hydroxamates 5d and 5e were the most effective in inducing p21 protein expression in the same cell line. Mechanistically, 5d, 5e, 8d and 8f increased mRNA expression of p21, BAX and BAK, downregulated cyclin D1 and BCL-2 and modulated pro- and anti-apoptotic microRNAs towards apoptosis induction. Finally, 5e strongly arrested proliferation in nine different haematological cancer cell lines, with dual-digit nanomolar potency towards MV4-11, Kasumi-1, and NB4, being more potent than mocetinostat, used as reference drug.

HDAC1-3 inhibition increases SARS-CoV-2 replication and productive infection in lung mesothelial and epithelial cells.

Background: Despite the significant progress achieved in understanding the pathology and clinical management of SARS-CoV-2 infection, still pathogenic and clinical issues need to be clarified. Treatment with modulators of epigenetic targets, i.e., epidrugs, is a current therapeutic option in several cancers and could represent an approach in the therapy of viral diseases. Results: Aim of this study was the analysis of the role of histone deacetylase (HDAC) inhibition in the modulation of SARS-CoV-2 infection of mesothelial cells (MCs).MeT5A cells, a pleura MC line, were pre-treated with different specific class I and IIb HDAC inhibitors. Unexpectedly, treatment with HDAC1-3 inhibitors significantly increased ACE2/TMPRSS2 expression, suggesting a role in favoring SARS-CoV-2 infection. We focused our analysis on the most potent ACE2/TMPRSS2 inducer among the inhibitors analysed, MS-275, a HDAC1-3 inhibitor. ACE2/TMPRSS2 expression was validated by Western Blot (WB) and immunofluorescence. The involvement of HDAC inhibition in receptor induction was confirmed by HDAC1/HDAC2 silencing. In accordance to the ACE2/TMPRSS2 expression data, MS-275 increased SARS-CoV-2 replication and virus propagation in Vero E6 cells.Notably, MS-275 was able to increase ACE2/TMPRSS2 expression and SARS-CoV-2 production, although to a lesser extent, also in the lung adenocarcinoma cell line Calu-3 cells.Mechanistically, treatment with MS-275 increased H3 and H4 histone acetylation at ACE2/TMPRSS2 promoters, increasing their transcription. Conclusion: This study highlights a previously unrecognized effect of HDAC1-3 inhibition in increasing SARS-CoV-2 cell entry, replication and productive infection correlating with increased expression of ACE2 and TMPRSS2. These data, while adding basic insight into COVID-19 pathogenesis, warn for the use of HDAC inhibitors in SARS-CoV-2 patients.

Restoration of WT1/miR-769-5p axis by HDAC1 inhibition promotes MMT reversal in mesenchymal-like mesothelial cells.

Histone acetylation/deacetylation play an essential role in modifying chromatin structure and in regulating cell plasticity in eukaryotic cells. Therefore, histone deacetylase (HDAC) pharmacological inhibitors are promising tools in the therapy of fibrotic diseases and in cancer. Peritoneal fibrosis is a pathological process characterized by many cellular and molecular alterations, including the acquisition of invasive/pro-fibrotic abilities by mesothelial cells (MCs) through induction of mesothelial to mesenchymal transition (MMT). The aim of this study was to characterize the molecular mechanism of the antifibrotic role of HDAC1 inhibition. Specifically, treatment with MS-275, an HDAC1-3 inhibitor previously known to promote MMT reversal, induced the expression of several TGFBRI mRNA-targeting miRNAs. Among them, miR-769-5p ectopic expression was sufficient to promote MMT reversal and to limit MC migration and invasion, whereas miR-769-5p silencing further enhanced mesenchymal gene expression. These results were confirmed by HDAC1 genetic silencing. Interestingly, miR-769-5p silencing maintained mesenchymal features despite HDAC1 inhibition, thus indicating that it is necessary to drive MMT reversal induced by HDAC1 inhibition. Besides TGFBRI, miR-769-5p was demonstrated to target SMAD2/3 and PAI-1 expression directly. When analyzing molecular mechanisms underlying miR-769-5p expression, we found that the transcription factor Wilms' tumor 1 (WT1), a master gene controlling MC development, binds to the miR-769-5p promoter favoring its expression. Interestingly, both WT1 expression and binding to miR-769-5p promoter were increased by HDAC1 inhibition and attenuated by TGFß1 treatment. Finally, we explored the significance of these observations in the cell-to-cell communication: we evaluated the ability of miR-769-5p to be loaded into extracellular vesicles (EVs) and to promote MMT reversal in recipient mesenchymal-like MCs. Treatment of fibrotic MCs with EVs isolated from miR-769-5p over-expressing MCs promoted the down-regulation of specific mesenchymal targets and the reacquisition of an epithelial-like morphology. In conclusion, we highlighted an HDAC1-WT1-miR-769-5p axis potentially relevant for therapies aimed at counteracting organ fibrosis.

Exposure to b-LED Light While Exerting Antimicrobial Activity on Gram-Negative and -Positive Bacteria Promotes Transient EMT-like Changes and Growth Arrest in Keratinocytes.

While blue LED (b-LED) light is increasingly being studied for its cytotoxic activity towards bacteria in therapy of skin-related infections, its effects on eukaryotic cells plasticity are less well characterized. Moreover, since different protocols are often used, comparing the effect of b-LED towards both microorganisms and epithelial surfaces may be difficult. The aim of this study was to analyze, in the same experimental setting, both the bactericidal activity and the effects on human keratinocytes. Exposure to b-LED induced an intense cytocidal activity against Gram-positive (i.e, Staphylococcus aureus) and Gram-negative (i.e., Pseudomonas aeruginosa) bacteria associated with catheter-related infections. Treatment with b-LED of a human keratinocyte cell line induced a transient cell cycle arrest. At the molecular level, exposure to b-LED induced a transient downregulation of Cyclin D1 and an upregulation of p21, but not signs of apoptosis. Interestingly, a transient induction of phosphor-histone γ-H2Ax, which is associated with genotoxic damages, was observed. At the same time, keratinocytes underwent a transient epithelial to mesenchymal transition (EMT)-like phenotype, characterized by E-cadherin downregulation and SNAIL/SLUG induction. As a functional readout of EMT induction, a scratch assay was performed. Surprisingly, b-LED treatment provoked a delay in the scratch closure. In conclusion, we demonstrated that b-LED microbicidal activity is associated with complex responses in keratinocytes that certainly deserve further analysis.

SYNCRIP Modulates the Epithelial-Mesenchymal Transition in Hepatocytes and HCC Cells.

Heterogeneous nuclear ribonucleoproteins (hnRNPs) control gene expression by acting at multiple levels and are often deregulated in epithelial tumors; however, their roles in the fine regulation of cellular reprogramming, specifically in epithelial-mesenchymal transition (EMT), remain largely unknown. Here, we focused on the hnRNP-Q (also known as SYNCRIP), showing by molecular analysis that in hepatocytes it acts as a "mesenchymal" gene, being induced by TGFß and modulating the EMT. SYNCRIP silencing limits the induction of the mesenchymal program and maintains the epithelial phenotype. Notably, in HCC invasive cells, SYNCRIP knockdown induces a mesenchymal-epithelial transition (MET), negatively regulating their mesenchymal phenotype and significantly impairing their migratory capacity. In exploring possible molecular mechanisms underlying these observations, we identified a set of miRNAs (i.e., miR-181-a1-3p, miR-181-b1-3p, miR-122-5p, miR-200a-5p, and miR-let7g-5p), previously shown to exert pro- or anti-EMT activities, significantly impacted by SYNCRIP interference during EMT/MET dynamics and gathered insights, suggesting the possible involvement of this RNA binding protein in their transcriptional regulation.

Ovarian Cancer-Driven Mesothelial-to-Mesenchymal Transition is Triggered by the Endothelin-1/ß-arr1 Axis.

Transcoelomic spread of serous ovarian cancer (SOC) results from the cooperative interactions between cancer and host components. Tumor-derived factors might allow the conversion of mesothelial cells (MCs) into tumor-associated MCs, providing a favorable environment for SOC cell dissemination. However, factors and molecular mechanisms involved in this process are largely unexplored. Here we investigated the tumor-related endothelin-1 (ET-1) as an inducer of changes in MCs supporting SOC progression. Here, we report a significant production of ET-1 from MCs associated with the expression of its cognate receptors, ETA and ETB, along with the protein ß-arrestin1. ET-1 triggers MC proliferation via ß-arrestin1-dependent MAPK and NF-kB pathways and increases the release of cancer-related factors. The ETA/ETB receptor activation supports the genetic reprogramming of mesothelial-to-mesenchymal transition (MMT), with upregulation of mesenchymal markers, as fibronectin, α-SMA, N-cadherin and vimentin, NF-kB-dependent Snail transcriptional activity and downregulation of E-cadherin and ZO-1, allowing to enhanced MC migration and invasion, and SOC transmesothelial migration. These effects are impaired by either blockade of ETAR and ETBR or by ß-arrestin1 silencing. Notably, in peritoneal metastases both ETAR and ETBR are co-expressed with MMT markers compared to normal control peritoneum. Collectively, our report shows that the ET-1 axis may contribute to the early stage of SOC progression by modulating MC pro-metastatic behaviour via MMT.

Pleural Mesothelial Cells Modulate the Inflammatory/Profibrotic Response During SARS-CoV-2 Infection.

Although lung fibrosis has a major impact in COVID-19 disease, its pathogenesis is incompletely understood. In particular, no direct evidence of pleura implication in COVID-19-related fibrotic damage has been reported so far. In this study, the expression of epithelial cytokeratins and Wilms tumor 1 (WT1), specific markers of mesothelial cells (MCs), was analyzed in COVID-19 and unrelated pleura autoptic samples. SARS-CoV-2 replication was analyzed by RT-PCR and confocal microscopy in MeT5A, a pleura MC line. SARS-CoV-2 receptors were analyzed by RT-PCR and western blot. Inflammatory cytokines from the supernatants of SARS-CoV-2-infected MeT5A cells were analysed by Luminex and ELLA assays. Immunohistochemistry of COVID-19 pleura patients highlighted disruption of pleura monolayer and fibrosis of the sub-mesothelial stroma, with the presence of MCs with fibroblastoid morphology in the sub-mesothelial stroma, but no evidence of direct infection in vivo. Interestingly, we found evidence of ACE2 expression in MCs from pleura of COVID-19 patients. In vitro analysis shown that MeT5A cells expressed ACE2, TMPRSS2, ADAM17 and NRP1, plasma membrane receptors implicated in SARS-CoV-2 cell entry and infectivity. Moreover, MeT5A cells sustained SARS-CoV-2 replication and productive infection. Infected MeT5A cells produced interferons, inflammatory cytokines and metalloproteases. Overall, our data highlight the potential role of pleura MCs as promoters of the fibrotic reaction and regulators of the immune response upon SARS-CoV-2 infection.