Specific cathepsin B inhibitor is cell-permeable and activates presentation of TTC in primary human dendritic cells

Human β-Defensin 3 Inhibition of P. gingivalis LPS-Induced IL-1β Production by BV-2 Microglia through Suppression of Cathepsins B and L

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.

Cholesteryl hemiazelate causes lysosome dysfunction impacting vascular smooth muscle cell homeostasis

In atherosclerotic lesions, vascular smooth muscle cells (VSMCs) represent half of the foam cell population, which is characterized by an aberrant accumulation of undigested lipids within lysosomes. Loss of lysosome function impacts VSMC homeostasis and disease progression. Understanding the molecular mechanisms underlying lysosome dysfunction in these cells is, therefore, crucial. We identify cholesteryl hemiazelate (ChA), a stable oxidation end-product of cholesteryl-polyunsaturated fatty acid esters, as an inducer of lysosome malfunction in VSMCs. ChA-treated VSMCs acquire a foam-cell-like phenotype, characterized by enlarged lysosomes full of ChA and neutral lipids. The lysosomes are perinuclear and exhibit degradative capacity and cargo exit defects. Lysosome luminal pH is also altered. Even though the transcriptional response machinery and autophagy are not activated by ChA, the addition of recombinant lysosomal acid lipase (LAL) is able to rescue lysosome dysfunction. ChA significantly affects VSMC proliferation and migration, impacting atherosclerosis. In summary, this work shows that ChA is sufficient to induce lysosomal dysfunction in VSMCs, that, in ChA-treated VSMCs, neither lysosome biogenesis nor autophagy are triggered, and, finally, that recombinant LAL can be a therapeutic approach for lysosomal dysfunction.

Enhancement of a Heroin Vaccine through Hapten Deuteration

The United States is in the midst of an unprecedented epidemic of opioid substance use disorder, and while pharmacotherapies including opioid agonists and antagonists have shown success, they can be inadequate and frequently result in high recidivism. With these challenges facing opioid use disorder treatments immunopharmacotherapy is being explored as an alternative therapy option and is based upon antibody-opioid sequestering to block brain entry. Development of a heroin vaccine has become a major research focal point; however, producing an efficient vaccine against heroin has been particularly challenging because of the need to generate not only a potent immune response but one against heroin and its multiple psychoactive molecules. In this study, we explored the consequence of regioselective deuteration of a heroin hapten and its impact upon the immune response against heroin and its psychoactive metabolites. Deuterium (H_dAc) and cognate protium heroin (H_Ac) haptens were compared head to head in an inclusive vaccine study. Strikingly the H_dAc vaccine granted greater efficacy in blunting heroin analgesia in murine behavioral models compared to the H_Ac vaccine. Binding studies confirmed that the H_dAc vaccine elicited both greater quantities and equivalent or higher affinity antibodies toward heroin and 6-AM. Blood-brain biodistribution experiments corroborated these affinity tests. These findings suggest that regioselective hapten deuteration could be useful for the resurrection of previous drug of abuse vaccines that have met limited success in the past.

Mycobacterium tuberculosis associated with severe tuberculosis evades cytosolic surveillance systems and modulates IL-1β production

Genetic diversity of Mycobacterium tuberculosis affects immune responses and clinical outcomes of tuberculosis (TB). However, how bacterial diversity orchestrates immune responses to direct distinct TB severities is unknown. Here we study 681 patients with pulmonary TB and show that M. tuberculosis isolates from cases with mild disease consistently induce robust cytokine responses in macrophages across multiple donors. By contrast, bacteria from patients with severe TB do not do so. Secretion of IL-1β is a good surrogate of the differences observed, and thus to classify strains as probable drivers of different TB severities. Furthermore, we demonstrate that M. tuberculosis isolates that induce low levels of IL-1β production can evade macrophage cytosolic surveillance systems, including cGAS and the inflammasome. Isolates exhibiting this evasion strategy carry candidate mutations, generating sigA recognition boxes or affecting components of the ESX-1 secretion system. Therefore, we provide evidence that M. tuberculosis strains manipulate host-pathogen interactions to drive variable TB severities.

BODIPY-Caged Photoactivated Inhibitors of Cathepsin B Flip the Light Switch on Cancer Cell Apoptosis

Acquired resistance to apoptotic agents is a long-standing challenge in cancer treatment. Cathepsin B (CTSB) is an enzyme which, among many essential functions, promotes apoptosis during cellular stress through regulation of intracellular proteolytic networks on the minute time scale. Recent data indicate that CTSB inhibition may be a promising method to steer cells away from apoptotic death toward necrosis, a mechanism of cell death that can overcome resistance to apoptotic agents, stimulate an immune response and promote antitumor immunity. Unfortunately, rapid and selective intracellular inactivation of CTSB has not been possible. However, here we report on the synthesis and characterization of photochemical and biological properties of BODIPY-caged inhibitors of CTSB that are cell permeable, highly selective and activated rapidly upon exposure to visible light. Intriguingly, these compounds display tunable photophysical and biological properties based on substituents bound directly to boron. Me₂BODIPY-caged compound 8 displays the dual-action capability of light-accelerated CTSB inhibition and singlet oxygen production from a singular molecular entity. The dual-action capacity of 8 leads to a rapid necrotic response in MDA-MB-231 triple negative breast cancer cells with high phototherapeutic indexes (>30) and selectivity vs noncancerous cells that neither CTSB inhibition nor photosensitization gives alone. Our work confirms that singlet oxygen production and CTSB inactivation is highly synergistic and a promising method for killing cancer cells. Furthermore, this ability to trigger intracellular inactivation of CTSB with light provides researchers with a powerful photochemical tool for probing biochemical processes on short time scales.

Upregulation of Cathepsin B-like Protease Activity During Apoptosis inGiardia duodenalis

Background:

In eukaryotic cells, apoptosis signaling pathways are controlled mainly by aspartic acid cysteine proteases (caspases). However, certain unicellular microorganisms, such as Giardia duodenalis, lack these proteins. Thus, other cysteine proteases may play an important role in the parasite apoptosis signaling pathway.

Objective:

To understand the effect of cathepsin B-like inhibition on the cell viability of Giardia duodenalis and its cell death process.

Methods:

Bioinformatics analysis was performed to identify apoptotic proteases. Analysis showed that cathepsin B-like protease genes from G. duodenalis were the best candidate. A homology modeling technique was used to explore in silico the inhibitory effect of E-64 against cathepsin B-like proteases from G. duodenalis genome and to examine the effect of curcumin on cathepsin B-like activity regulation. In addition, the effect of E-64 on parasite survival and DNA fragmentation was tested.

Results:

Eight cathepsin B-like protease coding genes were identified in silico. Interestingly, while these sequences lacked the cathepsin B characteristic occluding loop, they maintained the catalytic active- site responsible for cathepsin B activity, which was evidenced by the increase in the degradation of the Z-RR-AMC substrate, suggesting the upregulation of the activity of these proteins. Additionally, inhibition of E-64 against G. duodenalis trophozoites caused a decrease in DNA fragmentation compared to control cells and had a positive effect on parasite survival after exposure to curcumin.

Conclusion:

Overall, these results suggested that Giardia duodenalis might have a cell death mechanism in which cathepsin B-like proteases play an important role.

Cathepsin B in antigen-presenting cells controls mediators of the Th1 immune response during Leishmania major infection

Resistance and susceptibility to Leishmania major infection in the murine model is determined by the capacity of the host to mount either a protective Th1 response or a Th2 response associated with disease progression. Previous reports involving the use of cysteine cathepsin inhibitors indicated that cathepsins B (Ctsb) and L (Ctsl) play important roles in Th1/Th2 polarization during L. major infection in both susceptible and resistant mouse strains. Although it was hypothesized that these effects are a consequence of differential patterns of antigen processing, the mechanisms underlying these differences were not further investigated. Given the pivotal roles that dendritic cells and macrophages play during Leishmania infection, we generated bone-marrow derived dendritic cells (BMDC) and macrophages (BMM) from Ctsb^−/− and Ctsl^−/− mice, and studied the effects of Ctsb and Ctsl deficiency on the survival of L. major in infected cells. Furthermore, the signals used by dendritic cells to instruct Th cell polarization were addressed: the expression of MHC class II and co-stimulatory molecules, and cytokine production. We found that Ctsb^−/− BMDC express higher levels of MHC class II molecules than wild-type (WT) and Ctsl^−/− BMDC, while there were no significant differences in the expression of co-stimulatory molecules between cathepsin-deficient and WT cells. Moreover, both BMDC and BMM from Ctsb^−/− mice significantly up-regulated the levels of interleukin 12 (IL-12) expression, a key Th1-inducing cytokine. These findings indicate that Ctsb^−/− BMDC display more pro-Th1 properties than their WT and Ctsl^−/− counterparts, and therefore suggest that Ctsb down-regulates the Th1 response to L. major. Moreover, they propose a novel role for Ctsb as a regulator of cytokine expression.

The emergence of resistance to the available drugs against cutaneous leishmaniasis emphasizes the need of new chemotherapeutic approaches. Cysteine proteases from Leishmania are important virulence factors and, therefore, interesting drug targets. Studies on inhibitors against these enzymes during Leishmania major infection in mice had shown that host equivalents of these proteases are also affected, namely cathepsin B and cathepsin L. The inhibition of cathepsin B resulted in immune-mediated protection, while inhibition of cathepsin L caused susceptibility to the parasite. In the present study, we investigated the effect of cathepsin deficiency on the signals used by dendritic cells to orchestrate the T helper (Th)-mediated immune response against L. major and the control of parasite proliferation within infected macrophages. The results demonstrate that cathepsin B-deficient dendritic cells express higher levels of the antigen-presenting MHC class II molecules than WT and cathepsin L-deficient cells. Surprisingly, dendritic cells and macrophages deficient for cathepsin B showed higher expression of the protective Th1-inducing cytokine IL-12. Therefore, we propose a novel role of this protease as a regulator of cytokine expression. Altogether, these findings suggest that cathepsin B down-regulates the Th1 response to L. major, and, in its absence, antigen-presenting cells express signals protecting against the parasite.

N- and C-terminal degradation of ecdysteroid receptor isoforms, when transiently expressed in mammalian CHO cells, is regulated by the proteasome and cysteine and threonine proteases

Transcriptional activity of nuclear receptors is the result of transactivation capability and the concentration of the receptor protein. The concentration of ecdysteroid receptor (EcR) isoforms, constitutively expressed in mammalian CHO cells, is dependent on a number of factors. As shown previously, ligand binding stabilizes receptor protein concentration. In this paper, we investigate the degradation of EcR isoforms and provide evidence that N-terminal degradation is modulated by isoform-specific ubiquitination sites present in the A/B domains of EcR-A and -B1. This was demonstrated by the increase in EcR concentration by treatment with carbobenzoxy-L-leucyl-L-leucyl-L-leucinal (MG132), an inhibitor of ubiquitin-mediated proteasomal degradation and by deletion of ubiquitination sites. In addition, EcR is degraded by the peptidyl-dipeptidase cathepsin B (CatB) and the endopeptidase cathepsin S (CatS) at the C-terminus in an isoform-specific manner, despite identical C-termini. Ubiquitin-proteasome-mediated degradation and the proteolytic action are modulated by heterodimerization with Ultraspiracle (USP). The complex regulation of receptor protein concentration offers an additional opportunity to regulate transcriptional activity in an isoform- and target cell-specific way and allows the temporal limitation of hormone action.

FTY720 increases CD74 expression and sensitizes mantle cell lymphoma cells to milatuzumab-mediated cell death

Mantle cell lymphoma (MCL) is an aggressive B-cell malignancy with a short median survival despite multimodal therapy. FTY720, an immunosuppressive drug approved for the treatment of multiple sclerosis, promotes MCL cell death concurrent with down-modulation of phospho-Akt and cyclin D1 and subsequent cell-cycle arrest. However, the mechanism of FTY720-mediated MCL cell death remains to be fully clarified. In the present study, we show features of autophagy blockage by FTY720 treatment, including accumulation of autolysosomes and increased LC3-II and p62 levels. We also show that FTY720-induced cell death is mediated by lysosomal membrane permeabilization with subsequent translocation of lysosomal hydrolases to the cytosol. FTY720-mediated disruption of the autophagic-lysosomal pathway led to increased levels of CD74, a potential therapeutic target in MCL that is degraded in the lysosomal compartment. This finding provided rationale for examining combination therapy with FTY720 and milatuzumab, an anti-CD74 mAb. Treatment of MCL cell lines and primary tumor cells with FTY720 and milatuzumab resulted in statistically significant enhanced cell death, which was synergistic in blastic variant MCL cell lines. Significant in vivo therapeutic activity of combination treatment was also demonstrated in a preclinical, in vivo model of MCL. These findings support clinical evaluation of this combination in patients with MCL.

Invariant chain processing is independent of cathepsin variation between primary human B cells/dendritic cells and B-lymphoblastoid cells

As part of the endocytic antigen processing pathway, proteolytic cleavage of the invariant chain (Ii) is important for the generation of class II-associated invariant chain peptide (CLIP). CLIP remains associated with the major histocompatibility complex (MHC) class II molecule to prevent premature loading of antigenic peptides. Cysteine proteases, such as Cathepsin S (CatS), CatL, or CatV, play a pivotal role in the final stage of Ii degradation depending on the cell type studied. Less is known regarding the early stages of Ii processing. We therefore explored whether the serine protease CatG is involved in the initial step of Ii degradation in primary antigen presenting cells (APC), since the cathepsin distribution differs between primary APC and cell lines. While primary human B cells and dendritic cells (DC) do harbor CatG, this protease is absent in B-lymphoblastoid cells (BLC) or monocyte-derived DC generated in vitro. In addition, other proteases, such as CatC, CatL, and the asparagine endoprotease (AEP), are active in BLC and monocyte-derived DC. Here we demonstrate that CatG progressively degraded Ii in vitro resulting in several intermediates. However, pharmacological inhibition of CatG in primary B cells and DC did not alter Ii processing, indicating that CatG is dispensable in Ii degradation. Interestingly, stalling of cysteine proteases by inhibition in BLC vs. primary B cells and DC did not result in any differences in the generation of distinct Ii intermediates between the cells tested, suggesting that Ii processing is independent of the cathepsin variation within professional human APC.

Routes to manipulate MHC class II antigen presentation

MHC class II molecules (MHC-II) present antigenic fragments acquired in the endocytic route to the immune system for recognition and activation of CD4+ T cells. This ignites a series of immune responses. MHC-II strongly correlates to most autoimmune diseases. Understanding the biology of MHC-II is therefore expected to translate into novel means of autoimmunity control or immune response improvement. Although the basic cell biology of MHC-II antigen presentation is well understood, many novel aspects have been uncovered in recent years including means of antigen delivery, preparation for MHC-II loading, transport processes and vaccination strategies. We will discuss past, present and future of these insights into the biology of MHC-II.

Cathepsin A is expressed in primary human antigen-presenting cells

Cathepsins are expressed in antigen-presenting cells (APC). These cathepsins are known to regulate antigen processing and degradation of the invariant chain (Ii) into the class II-associated Ii peptide (CLIP), which occupies the peptide-binding groove of the major histocompatibility complex (MHC) class II molecule. Previous studies have identified the serine carboxypeptidase cathepsin A (CatA) in various tissues and cells; however, it is not clear whether CatA is also expressed in primary human APC. We demonstrate the expression of CatA in B lymphoblastoid cells (BLC), primary human B cells, both subsets of myeloid dendritic cells (mDC1 and mDC2), as well as in plasmacytoid DC. PMSF or lactacystin-mediated inhibition of serine proteases in BLC-derived lysosomal proteases resulted in the inhibition of amino acid release from the C-terminal end of two model peptides. This inhibition did not occur by using a proline rich peptide. Our data suggest that CatA is involved in the C-terminal fine-tuning of antigenic T cell epitopes in human APC.

Application of specific cell permeable cathepsin G inhibitors resulted in reduced antigen processing in primary dendritic cells

The serine protease cathepsin G (CatG) is expressed in primary antigen-presenting cells and regulates autoantigen processing in CatG pre-loaded fibroblasts. To further investigate the function of CatG in the major histocompatibility complex (MHC) class II loading compartments, a specific, cell permeable CatG-inhibitor is needed. In this study, several CatG-inhibitors were tested for their ability to penetrate the cell membrane of peripheral blood mononuclear cells (PBMC). We find that the commercially available reversible CatG-specific inhibitor I (CatG inhibitor) and the irreversible Suc-Val-Pro-Phe(P) (OPh)(2) (Suc-VPF) are both cell permeable and specifically inhibit intracellular CatG in the PBMC. Furthermore, selective inhibition of CatG resulted in reduced tetanus toxin C-fragment (TTC) and hemagglutinin (HA) processing and presentation to CD4(+) T cells. We conclude that these CatG inhibitors can be used for both antigen-processing studies and for modulation of T cell response in situ and in vivo.