Transmembrane serine protease TMPRSS2 implicated in SARS-CoV-2 infection is autoactivated intracellularly and requires N-glycosylation for regulation

SARS-CoV2 infection triggers inflammatory conditions and astrogliosis-related gene expression in long-term human cortical organoids

SARS-CoV2, severe acute respiratory syndrome coronavirus 2, is frequently associated with neurological manifestations. Despite the presence of mild to severe CNS-related symptoms in a cohort of patients, there is no consensus whether the virus can infect directly brain tissue or if the symptoms in patients are a consequence of peripheral infectivity of the virus. Here, we use long-term human stem cell-derived cortical organoids to assess SARS-CoV2 infectivity of brain cells and unravel the cell-type tropism and its downstream pathological effects. Our results show consistent and reproducible low levels of SARS-CoV2 infection of astrocytes, deep projection neurons, upper callosal neurons, and inhibitory neurons in 6 months of human cortical organoids. Interestingly, astrocytes showed the highest infection rate among all infected cell populations which led to changes in their morphology and upregulation of SERPINA3, CD44, and S100A10 astrogliosis markers. Further, transcriptomic analysis revealed overall changes in expression of genes related to cell metabolism, astrogliosis and, inflammation and further, upregulation of cell survival pathways. Thus, local and minor infectivity of SARS-CoV2 in the brain may induce widespread adverse effects and lead to the resilience of dysregulated neurons and astrocytes within an inflammatory environment.

Structural basis of TMPRSS11D specificity and autocleavage activation

Transmembrane Protease, Serine-2 (TMPRSS2) and TMPRSS11D are human proteases that enable SARS-CoV-2 and Influenza A/B virus infections, but their biochemical mechanisms for facilitating viral cell entry remain unclear. We show these proteases spontaneously and efficiently cleave their own zymogen activation motifs, activating their broader protease activity on cellular substrates. We determine TMPRSS11D co-crystal structures with a native and an engineered activation motif, revealing insights into its autocleavage activation and distinct substrate binding cleft features. Leveraging this structural data, we develop nanomolar potency peptidomimetic inhibitors of TMPRSS11D and TMPRSS2. We show that a broad serine protease inhibitor that underwent clinical trials for TMPRSS2-targeted COVID-19 therapy, nafamostat mesylate, was rapidly cleaved by TMPRSS11D and converted to low activity derivatives. In this work, we develop mechanistic insights into human protease viral tropism and highlight both the strengths and limitations of existing human serine protease inhibitors, informing future drug discovery efforts targeting these proteases.

Exploring TMPRSS2 Drug Target to Combat Influenza and Coronavirus Infection

Respiratory viral infections, including influenza and coronaviruses, present significant health risks worldwide. The recent COVID-19 pandemic highlights the urgent need for novel and effective antiviral agents. The host cell protease, transmembrane serine protease 2 (TMPRSS2), facilitates viral pathogenesis by playing a critical role in viral invasion and disease progression. This protease is coexpressed with the viral receptors of angiotensin-converting enzyme 2 (ACE2) for SARS-CoV-2 in the human respiratory tract and plays a significant role in activating viral proteins and spreading. TMPRSS2 activates the coronavirus spike (S) protein and permits membrane fusion and viral entry by cleaving the virus surface glycoproteins. It also activates the hemagglutinin (HA) protein, an enzyme necessary for the spread of influenza virus. TMPRSS2 inhibitors can reduce viral propagation and morbidity by blocking viral entry into respiratory cells and reducing viral spread, inflammation, and disease severity. This review examines the role of TMPRSS2 in viral replication and pathogenicity. It also offers potential avenues to develop targeted antivirals to inhibit TMPRSS2 function, suggesting a possible focus on targeted antiviral development. Ultimately, the review seeks to contribute to improving public health outcomes related to these viral infections.

Divergent responses to SARS-CoV-2 infection in bronchial epithelium with pre-existing respiratory diseases

Pre-existing respiratory diseases may influence coronavirus disease (COVID-19) susceptibility and severity. However, the molecular mechanisms underlying the airway epithelial response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection severity in patients with chronic respiratory diseases remain unelucidated. Using an in vitro model of differentiated primary bronchial epithelial cells, we aimed to investigate the molecular mechanisms of SARS-CoV-2 infection in pre-existing cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD). Our study revealed reduced susceptibility of CF and COPD airway epithelia to SARS-CoV-2, relative to that in healthy controls. Mechanistically, reduced transmembrane serine protease 2 (TMPRSS2) activity potentially contributed to this resistance of CF epithelium. Upregulated complement and inflammatory pathways in CF and COPD epithelia potentially primed the antiviral state prior to infection. Analysis of a COVID-19 patient cohort validated our findings, correlating specific inflammatory markers (IP-10, SERPINA1, and CFB) with COVID-19 severity. This study elucidates SARS-CoV-2 pathogenesis and identifies potential biomarkers for clinical monitoring.

Characterization of spike S1/S2 processing and entry pathways of lentiviral pseudoviruses bearing seasonal human coronaviruses NL63, 229E, and HKU1 spikes

Although much has been learned about the entry mechanism of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), many details of the entry mechanisms of seasonal human coronaviruses (HCoVs) remain less well understood. In the present study, we used 293T cell lines stably expressing angiotensin converting enzyme (ACE2), aminopeptidase N (APN), or transmembrane serine protease 2 (TMPRSS2), which support high-level transduction of lentiviral pseudoviruses bearing spike proteins of seasonal HCoVs, HCoV-NL63, -229E, or -HKU1, respectively, to compare spike processing and virus entry pathways among these viruses. Our results showed that the entry of HCoV-NL63, -229E, and -HKU1 pseudoviruses into cells is sensitive to endosomal acidification inhibitors (chloroquine and NH4Cl), indicating entry via the endocytosis route. Although TMPRSS2 expression on target cell surface was required for HCoV-HKU1 spike-mediated entry and cell-cell fusion, we found that only the serine protease domain of TMPRSS2 and not the serine protease activity of TMPRSS2 was required for viral entry via endocytic route. However, the serine protease activity of TMPRSS2 and a furin processing site (RKRR) at the S1/S2 junction were essential for efficient HCoV-HKU1 spike-mediated cell-cell fusion. Additionally, we show that dibasic and monobasic arginine residues at the S1/S2 junctions of spike proteins of HCoV-NL63 and -229E are essential for virus entry, but multi-basic furin processing site at the S1/S2 junction was dispensable for HCoV-HKU1 viral entry. Our findings highlight features of the entry mechanisms of seasonal HCoVs that may support the development of novel treatment strategies.IMPORTANCEDetails of the entry mechanisms of seasonal human coronaviruses (HCoVs) remain to be fully explored. To investigate spike-mediated virus entry of HCoV-NL63, -229E, and -HKU1 CoVs, we employed 293T cells that stably express angiotensin converting enzyme (ACE2), aminopeptidase N (APN), or transmembrane serine protease 2 (TMPRSS2) to study entry mechanisms of pseudoviruses bearing spike proteins of HCoV-NL63, -229E, and -HKU1, respectively. We found that HCoV-NL63, -229E, and -HKU1 pseudoviruses entered cells via the endocytic route independently of cellular serine protease activity and therefore likely depended on endosomal cathepsin activity. Furthermore, we showed that arginine amino acids in S1/S2 junctions of HCoV-NL63 and -229E spikes were essential for entry but not essential for HCoV-HKU1 entry. Our results provide new insights into the S1/S2 junctional residues, cellular receptors, and protease requirements for seasonal HCoV pseudovirus entry into cells that may support the development of novel inhibitors.

Human Transmembrane Serine Protease 2 (TMPRSS2) on Human Seminal Fluid Extracellular Vesicles Is Proteolytically Active

Human transmembrane serine protease 2 (TMPRSS2) has garnered substantial interest due to its clinical significance in various pathologies, notably its pivotal role in viral entry into host cells. The development of effective strategies to target TMPRSS2 is a current area of intense research and necessitates a consistent source of active TMPRSS2 with sufficient stability. Here, we comprehensively characterised human seminal-fluid extracellular vesicles (SF-EVs, also referred to as prostasomes), bearing a native source of surface-exposed, enzymatically active TMPRSS2 as demonstrated by high-sensitivity flow cytometry and a fluorometric activity assay. Additionally, we recombinantly produced human TMPRSS2 ectodomain in mammalian cells adopting a directed activation strategy. We observed comparable catalytic parameters and inhibition characteristics for both native SF-EV-associated and recombinant TMPRSS2 when exposed to serine protease inhibitor Nafamostat mesylate. Leveraging these findings, we developed a robust in vitro biochemical assay based on these SF-EVs for the screening of TMPRSS2-targeting compounds. Our results will accelerate the discovery and advancement of efficacious therapeutic approaches targeting TMPRSS2 and propel further exploration into the biological role of SF-EV-associated active TMPRSS2.

Leveraging Artificial Intelligence and Gene Expression Analysis to Identify Some Potential Bovine Coronavirus (BCoV) Receptors and Host Cell Enzymes Potentially Involved in the Viral Replication and Tissue Tropism

Bovine coronavirus (BCoV) exhibits dual tissue tropism, infecting both the respiratory and enteric tracts of cattle. Viral entry into host cells requires a coordinated interaction between viral and host proteins. However, the specific cellular receptors and co-receptors facilitating BCoV entry remain poorly understood. Similarly, the roles of host proteases such as Furin, TMPRSS2, and Cathepsin-L (CTS-L), known to assist in the replication of other coronaviruses, have not been extensively explored for BCoV. This study aims to identify novel BCoV receptors and host proteases that modulate viral replication and tissue tropism. Bovine cell lines were infected with BCoV isolates from enteric and respiratory origins, and the host cell gene expression profiles post-infection were analyzed using next-generation sequencing (NGS). Differentially expressed genes encoding potential receptors and proteases were further assessed using in-silico prediction and molecular docking analysis. These analyses focused on known coronavirus receptors, including ACE2, NRP1, DPP4, APN, AXL, and CEACAM1, to identify their potential roles in BCoV infection. Validation of these findings was performed using the qRT-PCR assays targeting individual genes. We confirmed the gene expression profiles of these receptors and enzymes in some BCoV (+/-) lung tissues. Results revealed high binding affinities of 9-O-acetylated sialic acid and NRP1 to BCoV spike (S) and hemagglutinin-esterase (HE) proteins compared to ACE2, DPP4, and CEACAM1. Additionally, Furin and TMPRSS2 were predicted to interact with the BCoV-S polybasic cleavage site (RRSRR|A), suggesting their roles in S glycoprotein activation. This is the first study to explore the interactions of BCoV with multiple host receptors and proteases. Functional studies are recommended to confirm their roles in BCoV infection and replication.

Intracellular autoactivation and surface location of hepsin, TMPRSS2, and TMPRSS13

AIMS

Hepsin (HPN), a Type II transmembrane serine protease (TTSP), is involved in hepatocyte metabolism and various diseases. It undergoes autoactivation on the surface of human hepatoma cells, a mechanism not observed in other cell types. This study aims to explore HPN activation and surface expression in endometrial epithelial cells.

MATERIALS AND METHODS

We studied HPN zymogen activation and cell surface expression in human embryonic kidney 293 and endometrial epithelial AN3CA and Ishikawa cells using site-directed mutagenesis, Western blotting, flow cytometry, and immunostaining. Treatments with brefeldin A (BFA) and monensin, along with co-transfection assays, were employed to assess HPN activation and expression before reaching the cell surface. We also analyzed the activation and expression of TMPRSS2 and TMPRSS13 and examined the effect of the serine protease inhibitor HAI-1 on these proteases.

KEY FINDINGS

HPN zymogen autoactivates in the endoplasmic reticulum (ER) and Golgi apparatus. Its active form reduces cell surface expression through trans-autodegradation, a mechanism also applicable to in TMPRSS2 and TMPRSS13. Additionally, HAI-1 interacts with these TTSPs in different ways: it inhibits HPN activation and stabilizes its cell-surface expression; it inhibits TMPRSS2 activation without affecting its cell-surface expression; and it facilitates TMPRSS13 activation, protecting it from degradation and stabilizing its cell surface expression.

SIGNIFICANCE

These results revealed an intracellular autoactivation and expression mechanism of HPN, TMPRSS2, and TMPRSS13, differing from the extracellular activated TTSPs. These findings provide new insights into the diverse mechanisms in regulating TTSP activation, potentially aiding in treating TTSP-related endometrial diseases.

TMPRSS2 as a Key Player in Viral Pathogenesis: Influenza and Coronaviruses

TMPRSS2, a human transmembrane protease enzyme, plays a crucial role in the spread of certain viruses, including influenza and coronaviruses. This enzyme promotes viral infection by cleaving viral glycoproteins, which helps viruses like SARS-CoV-2 and influenza A enter cells more effectively. Genetic differences in TMPRSS2 may affect people's susceptibility to COVID-19, underscoring the need for studies that consider diverse populations. Beyond infectious diseases, TMPRSS2 has also been linked to some cancers, suggesting it could be a valuable target for drug development. This review provides a summary of TMPRSS2 inhibitors currently under study, with some already in clinical trials to test their effectiveness against viral infections. As we uncover more about TMPRSS2's role in pathogenesis, it could open new doors for therapies to combat future outbreaks.

Involvement of metformin and aging in salivary expression of ACE2 and TMPRSS2

SARS-CoV-2-related proteins, ACE2 and TMPRSS2, are determinants of SARS-CoV-2 infection. Although these proteins are expressed in oral-related tissues, their expression patterns and modulatory mechanisms in the salivary glands remain unknown. We herein showed that full-length ACE2, which has both a fully functional enzyme catalytic site and high-affinity SARS-CoV-2 spike S1-binding sites, was more highly expressed in salivary glands than in oral mucosal epithelial cells and the lungs. Regarding TMPRSS2, zymogen and the cleaved form were both expressed in the salivary glands, whereas only zymogen was expressed in murine lacrimal glands and the lungs. Metformin, an AMPK activator, increased stimulated saliva secretion and full-length ACE2 expression and decreased cleaved TMPRSS2 expression in the salivary glands, and exerted the same effects on soluble ACE2 (sACE2) and sTMPRSS2 in saliva. Moreover, metformin decreased the expression of beta-galactosidase, a senescence marker, and ADAM17, a sheddase of ACE2 to sACE2, in the salivary glands. In aged mice, the expression of ACE2 was decreased in the salivary glands, whereas that of sACE2 was increased in saliva, presumably by the up-regulated expression of ADAM17. The expression of TMPRSS2 in the salivary glands and sTMPRSS2 in saliva were both increased. Collectively, these results suggest that the protein expression patterns of ACE2 and TMPRSS2 in the salivary glands differ from those in other oral-related cells and tissues, and also that metformin and aging affect the salivary expression of ACE2 and TMPRSS2, which have the potential as targets for preventing the transmission of SARS-CoV-2.

Identification of the critical residues of TMPRSS2 for entry and host range of human coronavirus HKU1

Human coronavirus (CoV) HKU1 infection typically causes common cold but can lead to pneumonia in children, older people, and immunosuppressed individuals. Recently, human transmembrane serine protease 2 (hTMPRSS2) was identified as the functional receptor for HKU1, but its region and residues critical for HKU1 S binding remain elusive. In this study, we find that HKU1 could utilize human and hamster, but not rat, mouse, or bat TMPRSS2 for virus entry, displaying a narrow host range. Using human-bat TMPRSS2 chimeras, we show that the serine peptidase (SP) domain of TMPRSS2 is essential for entry of HKU1. Further extensive mutagenesis analyses of the C-terminal regions of SP domains of human and bat TMPRSS2s identify residues 417 and 469 critical for entry of HKU1. Replacement of either D417 or Y469 with asparagine in hTMPRSS2 abolishes its abilities to mediate entry of HKU1 S pseudovirions and cell-cell fusion, whereas substitution of N417 with D or N469 with Y in bat TMPRSS2 (bTMPRSS2) renders it supporting HKU1 entry. Our findings contribute to a deeper understanding of coronavirus-receptor interactions and cross-species transmission.IMPORTANCEThe interactions of coronavirus (CoV) S proteins with their cognate receptors determine the host range and cross-species transmission potential. Recently, human transmembrane serine protease 2 (hTMPRSS2) was found to be the receptor for HKU1. Here, we show that the TMPRSS2 of hamster, but not rat, mouse, or bat, can serve as a functional entry receptor for HKU1. Moreover, swapping the residues at the positions of 417 and 469 of bTMPRSS2 with the corresponding residues of hTMPRSS2 confers it supporting entry of HKU1 S pseudovirions, indicating the critical role of these residues in HKU1 entry. Our study identified the critical residues in hTMPRSS2 responsible for receptor interaction and host range of HKU1.

Altered plasma levels of the SARS-CoV-2-related proteins ACE2 and TMPRSS2 in patients with Crohn's disease

The SARS-CoV-2 coronavirus infects cells through the cellular receptor angiotensin-converting enzyme 2 (ACE2), and the protease TMPRSS2 for the priming of viral spike protein. Thus, changes in these key proteins due to chronic conditions can increase risk for SARS-CoV2 infection; but significance of changes may differ is these changes correspond to full-length species or proteolytic fragments. Here, we determined that full-length ACE2 decreased in the plasma of uninfected Crohn's disease (CD) patients before treatment onset compared to controls. TMPRSS2 is mostly presented in plasma as full-length species and as an active peptidase fragment, but also as a prodomain fragment, which is the unique species remarkably decreased in plasma from CD patients. Patients treated with the anti-TNFα adalimumab showed recovery in ACE2 levels, while those treated with infliximab, or with the anti-IL-12/23 ustekinumab, still displayed a decrease in full-length species, as well as in cleaved fragments. Patients treated with azathioprine displayed similar ACE2 levels to that of controls, except a decrease in one of the ACE2 fragments. Uniquely, patients treated with azathioprine or with ustekinumab showed partial recovery in the reduction of the TMPRSS2-prodomain fragment characterized in treatment-naïve patients. Our data suggest that CD and common therapies are not related to increased susceptibility for SARS-CoV-2.

Biochemical characterization, stability, and kinetics of three substrates of the recombinant TMPRSS2 serine protease domain

Transmembrane serine protease 2 (TMPRSS2) is a membrane-bound protease belonging to the type II transmembrane serine protease (TTSP) family. It is a multidomain protein, including a serine protease domain responsible for its self-activation. The protein has been implicated as an oncogenic transcription factor and for its ability to cleave (prime) the SARS-CoV-2 spike protein. In order to characterize the TMPRSS2 biochemical properties, we expressed the serine protease domain (rTMPRSS2_SP) in Komagataella phaffii using the pPICZαA vector and purified it using immobilized metal affinity (Ni Sepharose™ excel) and size exclusion (Superdex 75) chromatography. We explored operational fluorescence resonance energy transfer FRET peptides as substrates. We chose the peptide Abz-QARK-(Dnp)-NH2 (Abz = ortho-aminobenzoic acid, the fluorescence donor, and Dnp = 2,4-dinitrophenyl, the quencher group) as a substrate to find the optimal conditions for maximum enzymatic activity. We found that metallic ions such as Ca2+ and Na+ increased enzymatic activity, but ionic surfactants and reducing agents decreased catalytic capacity. Finally, we determined the rTMPRSS2_SP stability for long-term storage. Altogether, our results represent the first comprehensive characterization of TMPRSS2's biochemical properties, providing valuable insights into its serine protease domain.

Characterization of the symmetrical benzimidazole twin drug TL1228: the role as viral entry inhibitor for fighting COVID-19

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is reliably one of the largest pandemics the world has suffered in recent years. In the search for non-biological antivirals, special emphasis was placed on drug repurposing to accelerate the clinical implementation of effective drugs.The life cycle of the virus has been extensively investigated and many human targets have been identified, such as the molecular chaperone GRP78, representing a host auxiliary factor for SARS-CoV-2 entry. Here we report the inhibitor capacity of TL1228, a small molecule discovered through an in silico screening approach, which could interfere with the interaction of SARS-CoV-2 and its target cells, blocking the recognition of the GRP78 cellular receptor by the viral Spike protein. TL1228 showed in vitro the ability to reduce significantly both pseudoviral and authentic viral activity even through the reduction of GRP78/ACE2 transcript levels. Importantly, TL1228 acts in modulating expression levels of innate immunity and as inflammation markers.

Addressing Post-Acute COVID-19 Syndrome in Cancer Patients, from Visceral Obesity and Myosteatosis to Systemic Inflammation: Implications in Cardio-Onco-Metabolism

Cardiovascular disease and cancer are the two leading causes of morbidity and mortality in the world. The emerging field of cardio-oncology described several shared risk factors that predispose patients to both cardiovascular disease and cancer. Post-acute COVID-19 syndrome is a chronic condition that occurs in many patients who have experienced a SARS-CoV-2 infection, mainly based on chronic fatigue, sedentary lifestyle, cramps, breathing difficulties, and reduced lung performance. Post-acute COVID-19 exposes patients to increased visceral adiposity, insulin resistance, myosteatosis, and white adipose tissue content (surrounded by M1 macrophages and characterized by a Th1/Th17 phenotype), which increases the risk of cardiovascular mortality and cancer recurrence. In this review, the main metabolic affections of post-acute COVID-19 syndrome in cancer patients at low and high risk of cardiomyopathies will be summarized. Furthermore, several non-pharmacological strategies aimed at reducing atherosclerotic and cardiac risk will be provided, especially through anti-inflammatory nutrition with a low insulin and glycemic index, appropriate physical activity, and immune-modulating bioactivities able to reduce visceral obesity and myosteatosis, improving insulin-related signaling and myocardial metabolism.

Extracellular proteolysis in cancer: Proteases, substrates, and mechanisms in tumor progression and metastasis

A vast ensemble of extracellular proteins influences the development and progression of cancer, shaped and reshaped by a complex network of extracellular proteases. These proteases, belonging to the distinct classes of metalloproteases, serine proteases, cysteine proteases, and aspartic proteases, play a critical role in cancer. They often become dysregulated in cancer, with increases in pathological protease activity frequently driven by the loss of normal latency controls, diminished regulation by endogenous protease inhibitors, and changes in localization. Dysregulated proteases accelerate tumor progression and metastasis by degrading protein barriers within the extracellular matrix (ECM), stimulating tumor growth, reactivating dormant tumor cells, facilitating tumor cell escape from immune surveillance, and shifting stromal cells toward cancer-promoting behaviors through the precise proteolysis of specific substrates to alter their functions. These crucial substrates include ECM proteins and proteoglycans, soluble proteins secreted by tumor and stromal cells, and extracellular domains of cell surface proteins, including membrane receptors and adhesion proteins. The complexity of the extracellular protease web presents a significant challenge to untangle. Nevertheless, technological strides in proteomics, chemical biology, and the development of new probes and reagents are enabling progress and advancing our understanding of the pivotal importance of extracellular proteolysis in cancer.

The endoplasmic reticulum-localized enzyme zDHHC6 mediates S-acylation of short transmembrane constructs from multiple type I and II membrane proteins

In this study, we investigated the S-acylation of two host cell proteins important for viral infection: TMPRSS2 (transmembrane serine protease 2), which cleaves severe acute respiratory syndrome coronavirus 2 spike to facilitate viral entry, and bone marrow stromal antigen 2, a general viral restriction factor. We found that both proteins were S-acylated by zDHHC6, an S-acyltransferase enzyme localized at the endoplasmic reticulum, in coexpression experiments. Mutagenic analysis revealed that zDHHC6 modifies a single cysteine in each protein, which are in proximity to the transmembrane domains (TMDs). For TMPRSS2, the modified cysteine is positioned two residues into the TMD, whereas the modified cysteine in bone marrow stromal antigen 2 has a cytosolic location two amino acids upstream of the TMD. Cysteine swapping revealed that repositioning the target cysteine of TMPRSS2 further into the TMD substantially reduced S-acylation by zDHHC6. Interestingly, zDHHC6 efficiently S-acylated truncated forms of these proteins that contained only the TMDs and short juxtamembrane regions. The ability of zDHHC6 to modify short TMD sequences was also seen for the transferrin receptor (another type II membrane protein) and for five different type I membrane protein constructs, including cluster of differentiation 4. Collectively, the results of this study show that zDHHC6 can modify diverse membrane proteins (type I and II) and requires only the presence of the TMD and target cysteine for efficient S-acylation. Thus, zDHHC6 may be a broad specificity S-acyltransferase specialized for the modification of a diverse set of transmembrane proteins at the endoplasmic reticulum.