Search Results (56)

Background/Objectives: Naegleria fowleri is a free-living protozoan that causes primary amoebic meningoencephalitis, a rapidly progressing central nervous system infection with high mortality rates and limited treatment options. Targeting virulence-associated proteins is essential for effective drug development. Fowlerpain-1 (FWP1), a papain-like cysteine protease (CP) implicated in extracellular matrix degradation and host–cell cytotoxicity, has been investigated as a therapeutic target. This study aimed to evaluate the FWP1 pocket geometry and stefin binding using an integrated in silico structural biology approach. Methods: A computational pipeline was used, including AlphaFold2-Multimer modeling of FWP1–stefin complexes, 20-ns molecular dynamics simulations under NPT conditions for conformational sampling, and molecular mechanics Poisson–Boltzmann surface area free energy calculations. Three natural CP inhibitors (stefins) were investigated. Structural stability was assessed using root mean square deviations, and binding profiles were characterized using protein–protein interaction analysis. Results: Stable FWP1–stefin interaction interfaces were predicted, with human stefin A showing favorable binding free energy. Two conserved motifs (PG and QVVAG) were identified as critical mediators of active-site recognition. Druggability analysis revealed a concave pocket with both hydrophobic and polar characteristics, consistent with a high-affinity ligand-binding site. Conclusions: This computational study supports a structural hypothesis for selective FWP1 inhibition and identifies stefins as promising scaffolds for developing structure-guided protease-targeted therapeutics against N. fowleri. Full article

Leaf senescence is a developmental process that allows nutrients to be remobilized and transported to sink organs. Previously, papain-like cysteine proteases (PLCPs) have been found to be highly expressed during leaf senescence in different plant species. In this study, we analyzed active PLCPs in barley (Hordeum vulgare L.) leaves during the terminal stage of natural senescence. Anion exchange chromatography of protein extracts from barley leaves, harvested six weeks after anthesis, followed by activity assays using the substrates Z-FR-AMC and Z-RR-AMC, revealed a single prominent peak corresponding to active PLCPs. This hydrolytic activity was completely inhibited by E-64, a potent and irreversible inhibitor of cysteine proteases. Fractions enriched for PLCP activity were affinity-labeled with DCG-04 and subjected to SDS-PAGE fractionation, separating two major bands at 43 and 38 kDa. These bands were analyzed using tandem mass spectrometry, allowing the identification of eleven PLCPs. Identified enzymes belong to eight PLCP subfamilies, including CTB/cathepsin B-like (HvPap-19 and -20), RD19/cathepsin F-like (HvPap-1), ALP/cathepsin H-like (HvPap-12 or aleurain), SAG12/cathepsin L-like A (HvPap-17), CEP/cathepsin L-like B (HvPap-14), RD21/cathepsin L-like D (HvPap-6 and -7), cathepsin L-like E (HvPap-13 and -16), and XBCP3 (HvPap-8). Among the identified PLCPs, HvPap-6 was the most abundant. Peptides corresponding to HvPap-6 were identified in both the 43 kDa and 38 kDa bands in approximately the same quantity based on total spectral count. Thus, our results indicate that two active HvPap-6 isoforms can be isolated from barley leaves at late senescence. Full article

This study investigated the effects of integrating biofloc with microalgae on growth performance and immune gene expression in red tilapia (Oreochromis sp.). The experiment consisted of four treatments: C (Biofloc), T1 (Chlorella vulgaris and Nannochloropsis sp.; 1:1), T2 (Biofloc + Chlorella vulgaris and Nannochloropsis sp.; 1:1), T3 (Biofloc + Chlorella vulgaris and Nannochloropsis sp.; 2:1) in 500 L plastic tanks for 60 days. T2 and T3 exhibited the lowest ammonia and nitrite levels, respectively. T3 exhibited the highest chlorophyll a and chlorophyll b levels, while T2 showed the highest carotenoid content. T2 showed the highest weight gain (142 ± 0.7 g) and SGR (1.61 ± 0.02) and the lowest FCR (1.79 ± 0.009). T2 exhibited the highest gene expression levels in the intestine, with 7.8-fold upregulation of the cathepsin L (ctsl) gene, 3-fold upregulation of toll-like receptor 7 (tlr7), 6.7-fold upregulation of interleukin-1 b (il-1b), 4.7-fold upregulation of tumor necrosis factor-alpha (tnf-a), and 2.8-fold upregulation of metallothionein (mt). In the head kidney, the mt upregulation was highest in T3 (7.2-fold), while tnf-a and tlr7 upregulations were highest in T2 (5.9-fold and 5-fold, respectively). In the liver, the gene expressions were highest in T3, with 6.4-fold upregulation of mt, 5-fold upregulation of ctsl, 2.7-fold upregulation of tlr7, 3-fold upregulation of il-1b, and 5.4-fold upregulation of tnf-a. These results suggest a synergistic effect of algae and bacteria on immune and antioxidative capacity in red tilapia. Full article

Global warming is increasing in severity, affecting insects across various biological species. This study investigated the heat resistance ability of the small hive beetle (Aethina tumida) by studying gene expression under heat stress and showed that A. tumida exhibits strong heat resistance and transcriptomic plasticity under heat stress. RNA-seq analysis identified 547, 1127, and 866 differentially expressed genes (DEGs) at 38 °C, 42 °C, and 46 °C, respectively, compared to 25 °C. Among them, 16, 25, and 5 heat shock protein (HSP) genes were differentially expressed under the three heat stress conditions. Specifically, one HSP70 gene (Loc109602670) was consistently upregulated across all temperatures. Furthermore, the lysosome-related pathway was the top enriched pathway under heat treatments, with key genes such as lysosomal aspartic protease-like, cathepsin L1-like, and lipase 3-like significantly upregulated. Overall, these findings suggest that A. tumida exhibits transcriptomic plasticity under sublethal heat stress, and key HSP genes with genes from lysosome pathways are likely to contribute to heat resistance. This study provides novel insights into the molecular basis of thermotolerance in A. tumida, contributing to our understanding of how this invasive pest adapts to high-temperature environments. Full article

Interleukin-1 beta(IL-1β) is the major driving force in neuroinflammation. Here, we report on (i) the role of (IL-1β) in activating a signaling cascade that leads to proliferation and metastasis in glioblastoma cancer pathogenesis as well as (ii) the therapeutic role for IL-1 Receptor Antagonist (IL-1RA) and Tolcapone against untoward aspects of tumor pathogenesis. Here, we report that IL-1β treatment at 50 ng/mL for 48 h increased proliferation and metastasis by 30-fold (p ≤ 0.05), leading to the formation of clones of rapidly dividing cancer cells, leading to the formation of organized glial fibrillary acid protein (GFAP)-immunoreactive, clone-like structures with protruding spikes. Further, IL-1β treatment significantly increased the expression of mRNA levels of the IL-1β-driven pathway TLR-MyD88-NF-κB-TNFα and IL-6 (p ≤ 0.05). IL-1β also increased autophagy via elevation of mRNA and protein levels of cathepsin B, LAMP-2, and LC3B. In contrast, IL-1RA and Tolcapone inhibited this proliferation and the expression of these mRNAs and proteins, inhibiting autophagy by downregulating these autophagy proteins and inducing apoptosis by upregulating the expression of pro-apoptotic proteins like caspase-8 and caspase-3. IL-1β and its receptor can be targeted for successful anticancer therapy, as shown here with the use of IL-1RA and/or Tolcapone. Full article

Background: Abdominal aortic aneurysm (AAA) is a chronic inflammatory disease characterized by the proteolytic breakdown of the extracellular matrix. A clinical biomarker is needed for risk stratification and prognosis. Methods: In this single-center, 5-year observational study, 452 patients were enrolled: 343 with AAA (≥3 cm), and 109 controls (<3 cm). Plasma levels of six inflammatory proteins (human epididymis protein 4 (HE4), matrix metalloproteinase (MMP) 1 and 3, cathepsin S, chitinase 3 like-1, cathepsin S, and B-cell activating factor (BAFF)) were quantified at baseline. Patients were followed for a total of 5 years (60 months), and major adverse cardiovascular events (MACEs, defined as the composite of myocardial infarction, cerebrovascular attack, and cardiovascular-related death) were recorded. A Cox proportional hazard model was created using biomarker levels, age, sex, hypertension, hypercholesterolemia, diabetes mellitus, smoking status, and coronary artery disease to determine whether the baseline levels of these proteins were associated with MACEs over 5 years. Results: HE4, MMP-3, BAFF, and cathepsin S levels were significantly elevated in AAA patients compared to controls (all p < 0.05). HE4/WFDC2, MMP-3, and Chitinase 3-like 1 were significantly linearly associated with AAA diameter at baseline. With every normalized unit increase in HE4/WFDC2, MMP-3, and Chitinase 3-like 1, there was an increase in abdominal aortic diameter by 0.154 (95% CI: 0.032–0.276, p = 0.013), 0.186 (95% CI: 0.064–0.309, p = 0.003), and 0.231 (0.110–0.353, p < 0.001) centimeters, respectively. Among patients with AAA, elevated HE4 was associated with higher risk of MACEs (adjusted HR 1.249; 95% CI: 1.057–1.476; p = 0.009). Patients with high baseline HE4 (≥9.338 ng/mL) had significantly lower freedom from MACEs at 5 years (76.7% vs. 84.8%, p = 0.022). Conclusions: HE4 may be a potential prognostic biomarker that can be used to risk stratify patients with AAA to better personalize treatment strategies to reduce adverse events. Full article

Cathepsin B is a member of the cysteine protease family and plays an important role in the innate immunity of aquatic invertebrates. A previous study identified that Cathepsin B-like (CTSB-l) may be involved in the response of alkali treatment in Macrobrachium nipponense. The present study aims to identify the potential regulatory roles of CTSB-l in the response of alkali treatment in M. nipponense through performing the quantitative real-time PCR analysis (qPCR), in situ hybridization (ISH) analysis, and RNA interference (RNAi) analysis. The full length of the MnCTSB-l cDNA was 1272 bp with an open reading frame of 987 bp, encoding 328 amino acids. Phylogenetic tree analysis indicated that the amino acid sequence of MnCTSB-l is highly homologous to those of crustacean cathepsin B-like. qPCR analysis showed that MnCTSB-l mRNA is expressed in all tested tissues with the highest level of expression in hepatopancreas in both male and female prawns. The expressions of MnCTSB-l were significantly stimulated in gills under the alkali concentration of both 5 mmol/L and 10 mmol/L, predicting that this gene may be involved in the response of alkali treatment in M. nipponense, which was consistent with the previous study. ISH showed that MnCTSB-l signals were mainly observed in the hemolymph vessels and membranes of gills, as well as in the basement membranes of hepatopancreas, in both male and female prawns. RNAi analysis revealed that the injection of double-stranded RNA of CTSB (dsCTSB) resulted in a significant decrease in MnCTSB-l expressions. In addition, prawn cumulative mortality was significantly higher in the dsCTSB-injected group, compared to that of dsGFP-injected group, under alkali treatments of both 5 mmol/L and 10 mmol/L, indicating CTSB-l plays an essential role in regulating alkalinity acclimation in M. nipponense. The present study identifies the regulatory functions of CTSB-l in the response of alkali treatment in M. nipponense, promoting the survival rate and aquaculture of this species in a water environment with high alkalinity. Full article

The impact of dietary lipid sources on nutrient metabolism and reproductive development is a critical focus in aquaculture broodstock nutrition. Previous studies have demonstrated that fish oil supplementation modulates the expression of genes involved in steroid hormone synthesis, glucose, and lipid metabolism promoting ovarian development in female Scatophagus argus (spotted scat). However, the effects of fish oil on hepatic function at the protein level remain poorly characterized. In this study, female S. argus were fed diets containing 8% fish oil (FO, experimental group) or 8% soybean oil (SO, control group) for 60 days. Comparative proteomic analysis of liver tissue identified significant differential protein expression between groups. The FO group exhibited upregulation of lipid metabolism-related proteins, including COMM domain-containing protein 1 (Commd1), tetraspanin 8 (Tspan8), myoglobin (Mb), transmembrane protein 41B (Tmem41b), stromal cell-derived factor 2-like protein 1 (Sdf2l1), and peroxisomal biogenesis factor 5 (Pex5). Additionally, glucose metabolism-associated proteins, such as Sdf2l1 and non-POU domain-containing octamer-binding protein (Nono), were elevated in the FO group. Moreover, proteins linked to inflammation and antioxidant responses, including G protein-coupled receptor 108 (Gpr108), protein tyrosine phosphatase non-receptor type 2 (Ptpn2), Pex5, p120 catenin (Ctnnd1), tripartite motif-containing protein 16 (Trim16), and aquaporin 11 (Aqp11), were elevated in the FO group, while proteins involved in oxidative stress, such as reactive oxygen species modulator 1 (Romo1), cathepsin A (Ctsa), and Cullin 4A (Cul4a), were downregulated. These proteomic findings align with prior transcriptomic data, indicating that dietary fish oil enhances hepatic lipid metabolism, mitigates oxidative stress, and strengthens antioxidant capacity. Furthermore, these hepatic adaptations may synergistically support ovarian maturation in S. argus. This study provides novel proteomic-level evidence supporting the role of fish oil in modulating hepatic lipid and energy metabolism, thereby elucidating the role of fish oil in optimizing hepatic energy metabolism and redox homeostasis to influence reproductive processes, advancing our understanding of n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA) in teleost liver physiology. Full article

Leaf senescence is a developmental process allowing nutrient remobilization to sink organs. Previously cysteine proteases have been found to be highly expressed during leaf senescence in different plant species. Using biochemical and immunoblotting approaches, we characterized developmental senescence of barley (Hordeum vulgare L. var. ‘GemCraft’) leaves collected from 0 to 6 weeks after the onset of flowering. A decrease in total protein and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) large subunits occurred in parallel with an increase in proteolytic activity measured using the fluorogenic substrates Z-RR-AMC, Z-FR-AMC, and casein labeled with fluorescein isothiocyanate (casein-FITC). Aminopeptidase activity detected with R-AMC peaked at week 3 and then decreased, reaching a low level by week 6. Maximal proteolytic activity with Z-FR-AMC and Z-RR-AMC was detected from pH 4.0 to pH 5.5 and pH 6.5 to pH 7.4, respectively, while two pH optima (pH 3.6 to pH 4.5 and pH 6.5 to pH 7.4) were found for casein-FITC. Compound E-64, an irreversible cysteine protease inhibitor, and CAA0225, a selective cathepsin L inhibitor, effectively inhibited proteolytic activity with IC₅₀ values in the nanomolar range. CA-074, a selective cathepsin B inhibitor, was less potent under the same experimental conditions, with IC₅₀ in the micromolar range. Inhibition by leupeptin and phenylmethylsulfonyl fluoride (PMSF) was weak, and pepstatin A, an inhibitor of aspartic acid proteases, had no effect at the concentrations studied (up to 0.2 mM). Maximal proteolytic activity with the aminopeptidase substrate R-AMC was detected from pH 7.0 to pH 8.0. The pH profile of DCG-04 (a biotinylated activity probe derived from E-64) binding corresponded to that found with Z-FR-AMC, suggesting that the major active proteases are related to cathepsins B and L. Moreover, immunoblotting detected increased levels of barley SAG12 orthologs and aleurain, confirming a possible role of these enzymes in senescing leaves. Full article

Meloidogyne javanica is one of the most widespread and economically important sedentary endoparasites. In this study, a comparative transcriptome analysis of M. javanica between pre-parasitic second-stage juveniles (Pre-J2) and parasitic juveniles (Par-J3/J4) was conducted. A total of 48,698 unigenes were obtained, of which 18,826 genes showed significant differences in expression (p < 0.05). In the differentially expressed genes (DEGs) from transcriptome data at Par-J3/J4 and Pre-J2, a large number of unigenes were annotated to the C-type lectin (CTL, Mg01965), the cathepsin L-like protease (Mi-cpl-1), the venom allergen-like protein (Mi-mps-1), Map-1 and the cellulase (endo-β-1,4-glucanase). Among seven types of lectins found in the DEGs, there were 10 CTLs. The regulatory roles of Mj-CTL-1, Mj-CTL-2 and Mj-CTL-3 in plant immune responses involved in the parasitism of M. javanica were investigated. The results revealed that Mj-CTL-2 could suppress programmed cell death (PCD) triggered by Gpa2/RBP-1 and inhibit the flg22-stimulated ROS burst. In situ hybridization and developmental expression analyses showed that Mj-CTL-2 was specifically expressed in the subventral gland of M. javanica, and its expression was up-regulated at Pre-J2 of the nematode. In addition, in planta silencing of Mj-CTL-2 substantially increased the plant resistance to M. javanica. Moreover, yeast co-transformation and bimolecular fluorescence complementation assay showed that Mj-CTL-2 specifically interacted with the Solanum lycopersicum catalase, SlCAT2. It was demonstrated that M. javanica could suppress the innate immunity of plants through the peroxide system, thereby promoting parasitism. Full article

Cathepsin B (CatB) is thought to be essential for the induction of Porphyromonas gingivalis lipopolysaccharide (Pg LPS)-induced Alzheimer’s disease-like pathologies in mice, including interleukin-1β (IL-1β) production and cognitive decline. However, little is known about the role of CatB in Pg virulence factor-induced IL-1β production by microglia. We first subjected IL-1β-luciferase reporter BV-2 microglia to inhibitors of Toll-like receptors (TLRs), IκB kinase, and the NLRP3 inflammasome following stimulation with Pg LPS and outer membrane vesicles (OMVs). To clarify the involvement of CatB, we used several known CatB inhibitors, including CA-074Me, ZRLR, and human β-defensin 3 (hBD3). IL-1β production in BV-2 microglia induced by Pg LPS and OMVs was significantly inhibited by the TLR2 inhibitor C29 and the IκB kinase inhibitor wedelolactonne, but not by the NLRPs inhibitor MCC950. Both hBD3 and CA-074Me significantly inhibited Pg LPS-induced IL-1β production in BV-2 microglia. Although CA-074Me also suppressed OMV-induced IL-1β production, hBD3 did not inhibit it. Furthermore, both hBD3 and CA-074Me significantly blocked Pg LPS-induced nuclear NF-κB p65 translocation and IκBα degradation. In contrast, hBD3 and CA-074Me did not block OMV-induced nuclear NF-κB p65 translocation or IκBα degradation. Furthermore, neither ZRLR, a specific CatB inhibitor, nor shRNA-mediated knockdown of CatB expression had any effect on Pg virulence factor-induced IL-1β production. Interestingly, phagocytosis of OMVs by BV-2 microglia induced IL-1β production. Finally, the structural models generated by AlphaFold indicated that hBD3 can bind to the substrate-binding pocket of CatB, and possibly CatL as well. These results suggest that Pg LPS induces CatB/CatL-dependent synthesis and processing of pro-IL-1β without activation of the NLRP3 inflammasome. In contrast, OMVs promote the synthesis and processing of pro-IL-1β through CatB/CatL-independent phagocytic mechanisms. Thus, hBD3 can improve the IL-1β-associated vicious inflammatory cycle induced by microglia through inhibition of CatB/CatL. Full article

Cathepsin L (CTSL) expression is dysregulated in a variety of cancers. Extensive empirical evidence indicates their direct participation in cancer growth, angiogenic processes, metastatic dissemination, and the development of treatment resistance. Currently, no natural CTSL inhibitors are approved for clinical use. Consequently, the development of novel CTSL inhibition strategies is an urgent necessity. In this study, a combined machine learning (ML) and structure-based virtual screening strategy was employed to identify potential natural CTSL inhibitors. The random forest ML model was trained on IC₅₀ values. The accuracy of the trained model was over 90%. Furthermore, we used this ML model to screen the Biopurify and Targetmol natural compound libraries, yielding 149 hits with prediction scores >0.6. These hits were subsequently selected for virtual screening using a structure-based approach, yielding 13 hits with higher binding affinity compared to the positive control (AZ12878478). Two of these hits, ZINC4097985 and ZINC4098355, have been shown to strongly bind CTSL proteins. In addition to drug-like properties, both compounds demonstrated high affinity, ligand efficiency, and specificity for the CTSL binding pocket. Furthermore, in molecular dynamics simulations spanning 200 ns, these compounds formed stable protein-ligand complexes. ZINC4097985 and ZINC4098355 can be considered promising candidates for CTSL inhibition after experimental validation, with the potential to provide therapeutic benefits in cancer management. Full article

The protein disulfide isomerase (PDI) family is a group of thioredoxin endoplasmic reticulum (ER)-resident enzymes and molecular chaperones that play crucial roles in the correct folding of proteins. PDIs are upregulated in multiple cancer types and are considered a novel target for cancer therapy. In this study, we found that a potent pan-PDI inhibitor, E64FC26, significantly decreased the proliferation of pancreatic ductal adenocarcinoma (PDAC) cells. As expected, E64FC26 treatment increased ER stress and the unfolded protein response (UPR), as evidenced by upregulation of glucose-regulated protein, 78-kDa (GRP78), phosphorylated (p)-PKR-like ER kinase (PERK), and p-eukaryotic initiation factor 2α (eIF2α). Persistent ER stress was found to lead to apoptosis, ferroptosis, and autophagy, all of which are dependent on lysosomal functions. First, there was little cleaved caspase-3 in E64FC26-treated cells according to Western blotting, but a higher dose of E64FC26 was needed to induce caspase activity. Then, E64FC26-induced cell death could be reversed by adding the iron chelator, deferoxamine, and the reactive oxygen species scavengers, ferrostatin-1 and N-acetylcysteine. Furthermore, the autophagosome-specific marker, light chain 3B (LC3B)-II, increased, but the autolysosome marker, sequestosome 1 (SQSTM1)/p62, was not degraded in E64FC26-treated cells. Using the FUW mCherry-LC3 plasmid and acridine orange staining, we also discovered a lower number of acidic vesicles, such as autolysosomes and mature lysosomes, in E64FC26-treated cells. Finally, E64FC26 treatment increased the cathepsin L precursor (pre-CTSL) but decreased mature CTSL expression according to Western blotting, indicating a defective lysosome. These results suggested that the PDI inhibitor, E64FC26, might initially impede proper folding of proteins, and then induce ER stress and disrupt proteostasis, subsequently leading to lysosomal defects. Due to defective lysosomes, the extents of apoptosis and ferroptosis were limited, and fusion with autophagosomes was blocked in E64FC26-treated cells. Blockade of autolysosomal formation further led to the autophagic cell death of PDAC cells. Full article

The significant role of papain-like cysteine proteases, including papain, cathepsin L and SARS-CoV-2 PLpro, in biomedicine and biotechnology makes them interesting model systems for sensor development. These enzymes have a free thiol group that is suitable for many sensor designs including strong binding to gold nanoparticles or low-molecular-weight inhibitors. Focusing on the importance of the preservation of native protein structure for inhibitor-binding and molecular-imprinting, which has been applied in some efficient examples of sensor development, the aim of this work was to examine the effects of the free-thiol-group’s reversible blocking on papain denaturation that is the basis of its activity loss and aggregation. To utilize biophysical methods common in protein structural transitions characterization, such as fluorimetry and high-resolution infrared spectroscopy, low-molecular-weight electrophilic thiol blocking reagent S-Methyl methanethiosulfonate (MMTS) was used in solution. MMTS binding led to a two-fold increase in 8-Anilinonaphthalene-1-sulfonic acid fluorescence, indicating increased hydrophobic residue exposure. A more in-depth analysis showed significant transitions on the secondary structure level upon MMTS binding, mostly characterized by the lowered content of α-helices and unordered structures (either for approximately one third), and the increase in aggregation-specific β-sheets (from 25 to 52%) in a dose-dependant manner. The recovery of this inhibited protein showed that reversibility of inhibition is accompanied by reversibility of protein denaturation. Nevertheless, a 100-fold molar excess of the inhibitor led to the incomplete recovery of proteolytic activity, which can be explained by irreversible denaturation. The structural stability of the C-terminal β-sheet rich domain of the papain-like cysteine protease family opens up an interesting possibility to use its foldamers as a strategy for sensor development and other multiple potential applications that rely on the great commercial value of papain-like cysteine proteases. Full article

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a SARS-like coronavirus, continues to produce mounting infections and fatalities all over the world. Recent data point to SARS-CoV-2 viral infections in the human testis. As low testosterone levels are associated with SARS-CoV-2 viral infections in males and human Leydig cells are the main source of testosterone, we hypothesized that SARS-CoV-2 could infect human Leydig cells and impair their function. We successfully detected SARS-CoV-2 nucleocapsid in testicular Leydig cells of SARS-CoV-2-infected hamsters, providing evidence that Leydig cells can be infected with SARS-CoV-2. We then employed human Leydig-like cells (hLLCs) to show that the SARS-CoV-2 receptor angiotensin-converting enzyme 2 is highly expressed in hLLCs. Using a cell binding assay and a SARS-CoV-2 spike-pseudotyped viral vector (SARS-CoV-2 spike pseudovector), we showed that SARS-CoV-2 could enter hLLCs and increase testosterone production by hLLCs. We further combined the SARS-CoV-2 spike pseudovector system with pseudovector-based inhibition assays to show that SARS-CoV-2 enters hLLCs through pathways distinct from those of monkey kidney Vero E6 cells, a typical model used to study SARS-CoV-2 entry mechanisms. We finally revealed that neuropilin-1 and cathepsin B/L are expressed in hLLCs and human testes, raising the possibility that SARS-CoV-2 may enter hLLCs through these receptors or proteases. In conclusion, our study shows that SARS-CoV-2 can enter hLLCs through a distinct pathway and alter testosterone production. Full article