Cyclophilin A regulates TCR signal strength in CD4+ T cells via a proline-directed conformational switch in Itk

Cyclosporin A-Based PROTACs Can Deplete Abundant Cellular Cyclophilin A without Suppressing T Cell Activation

Cyclophilin A (CypA), the cellular receptor of the immunosuppressant cyclosporin A (CsA), is an abundant cytosolic protein and is involved in a variety of diseases. For example, CypA supports cancer proliferation and mediates viral infections, such as the human immunodeficiency virus 1 (HIV-1). Here, we present the design of PROTAC (proteolysis targeting chimera) compounds against CypA to induce its intracellular proteolysis and to investigate their effect on immune cells. Interestingly, upon connecting to E3 ligase ligands, both peptide-based low-affinity binders and CsA-based high-affinity binders can degrade CypA at nM concentration in HeLa cells and fibroblast cells. As the immunosuppressive effect of CsA is not directly associated with the binding of CsA to CypA but the inhibition of phosphatase calcineurin by the CypA:CsA complex, we investigated whether a CsA-based PROTAC compound could induce CypA degradation without affecting the activation of immune cells. P3, the most efficient PROTAC compound discovered from this study, could deplete CypA in lymphocytes without affecting cell proliferation and cytokine production. This work demonstrates the feasibility of the PROTAC approach in depleting the abundant cellular protein CypA at low drug dosage without affecting immune cells, allowing us to investigate the potential therapeutic effects associated with the endogenous protein in the future.

Proteostatic Remodeling of Small Heat Shock Chaperones─Crystallins by Ran-Binding Protein 2─and the Peptidyl-Prolyl cis-trans Isomerase and Chaperone Activities of Its Cyclophilin Domain

Disturbances in protein phase transitions promote protein aggregation─a neurodegeneration hallmark. The modular Ran-binding protein 2 (Ranbp2) is a cytosolic molecular hub for rate-limiting steps of phase transitions of Ran-GTP-bound protein ensembles exiting nuclear pores. Chaperones also regulate phase transitions and proteostasis by suppressing protein aggregation. Ranbp2 haploinsufficiency promotes the age-dependent neuroprotection of the chorioretina against phototoxicity by proteostatic regulations of neuroprotective substrates of Ranbp2 and by suppressing the buildup of polyubiquitylated substrates. Losses of peptidyl-prolyl cis-trans isomerase (PPIase) and chaperone activities of the cyclophilin domain (CY) of Ranbp2 recapitulate molecular effects of Ranbp2 haploinsufficiency. These CY impairments also stimulate deubiquitylation activities and phase transitions of 19S cap subunits of the 26S proteasome that associates with Ranbp2. However, links between CY moonlighting activity, substrate ubiquitylation, and proteostasis remain incomplete. Here, we reveal the Ranbp2 regulation of small heat shock chaperones─crystallins in the chorioretina by proteomics of mice with total or selective modular deficits of Ranbp2. Specifically, loss of CY PPIase of Ranbp2 upregulates αA-Crystallin, which is repressed in adult nonlenticular tissues. Conversely, impairment of CY's chaperone activity opposite to the PPIase pocket downregulates a subset of αA-Crystallin's substrates, γ-crystallins. These CY-dependent effects cause age-dependent and chorioretinal-selective declines of ubiquitylated substrates without affecting the chorioretinal morphology. A model emerges whereby inhibition of Ranbp2's CY PPIase remodels crystallins' expressions, subdues molecular aging, and preordains the chorioretina to neuroprotection by augmenting the chaperone capacity and the degradation of polyubiquitylated substrates against proteostatic impairments. Further, the druggable Ranbp2 CY holds pan-therapeutic potential against proteotoxicity and neurodegeneration.

The extracellular cyclophilin A-integrin β2 complex as a therapeutic target of viral pneumonia

The acute respiratory virus infection can induce uncontrolled inflammatory responses, such as cytokine storm and viral pneumonia, which are the major causes of death in clinical cases. Cyclophilin A (CypA) is mainly distributed in the cytoplasm of resting cells and released into the extracellular space in response to inflammatory stimuli. Extracellular CypA (eCypA) is upregulated and promotes inflammatory response in severe COVID-19 patients. However, how eCypA promotes virus-induced inflammatory response remains elusive. Here, we observe that eCypA is induced by influenza A and B viruses and SARS-CoV-2 in cells, mice, or patients. Anti-CypA mAb reduces pro-inflammatory cytokines production, leukocytes infiltration, and lung injury in virus-infected mice. Mechanistically, eCypA binding to integrin β2 triggers integrin activation, thereby facilitating leukocyte trafficking and cytokines production via the focal adhesion kinase (FAK)/GTPase and FAK/ERK/P65 pathways, respectively. These functions are suppressed by the anti-CypA mAb that specifically blocks eCypA-integrin β2 interaction. Overall, our findings reveal that eCypA-integrin β2 signaling mediates virus-induced inflammatory response, indicating that eCypA is a potential target for antibody therapy against viral pneumonia.

Cyclophilin A supports translation of intrinsically disordered proteins and affects haematopoietic stem cell ageing

Loss of protein function is a driving force of ageing. We have identified peptidyl-prolyl isomerase A (PPIA or cyclophilin A) as a dominant chaperone in haematopoietic stem and progenitor cells. Depletion of PPIA accelerates stem cell ageing. We found that proteins with intrinsically disordered regions (IDRs) are frequent PPIA substrates. IDRs facilitate interactions with other proteins or nucleic acids and can trigger liquid-liquid phase separation. Over 20% of PPIA substrates are involved in the formation of supramolecular membrane-less organelles. PPIA affects regulators of stress granules (PABPC1), P-bodies (DDX6) and nucleoli (NPM1) to promote phase separation and increase cellular stress resistance. Haematopoietic stem cell ageing is associated with a post-transcriptional decrease in PPIA expression and reduced translation of IDR-rich proteins. Here we link the chaperone PPIA to the synthesis of intrinsically disordered proteins, which indicates that impaired protein interaction networks and macromolecular condensation may be potential determinants of haematopoietic stem cell ageing.

Inhibitors of Cyclophilin A: Current and Anticipated Pharmaceutical Agents for Inflammatory Diseases and Cancers

Cyclophilin A, a widely prevalent cellular protein, exhibits peptidyl-prolyl cis-trans isomerase activity. This protein is predominantly located in the cytosol; additionally, it can be secreted by the cells in response to inflammatory stimuli. Cyclophilin A has been identified to be a key player in many of the biological events and is therefore involved in several diseases, including vascular and inflammatory diseases, immune disorders, aging, and cancers. It represents an attractive target for therapeutic intervention with small molecule inhibitors such as cyclosporin A. Recently, a number of novel inhibitors of cyclophilin A have emerged. However, it remains elusive whether and how many cyclophilin A inhibitors function in the inflammatory diseases and cancers. In this review, we discuss current available data about cyclophilin A inhibitors, including cyclosporin A and its derivatives, quinoxaline derivatives, and peptide analogues, and outline the most recent advances in clinical trials of these agents. Inhibitors of cyclophilin A are poised to enhance our comprehension of the molecular mechanisms that underpin inflammatory diseases and cancers associated with cyclophilin A. This advancement will aid in the development of innovative pharmaceutical treatments in the future.

Proteostatic remodeling of small heat shock chaperones - crystallins by Ran-binding protein 2 and the peptidyl-prolyl cis-trans isomerase and chaperone activities of its cyclophilin domain

Disturbances in phase transitions and intracellular partitions of nucleocytoplasmic shuttling substrates promote protein aggregation - a hallmark of neurodegenerative diseases. The modular Ran-binding protein 2 (Ranbp2) is a cytosolic molecular hub for rate-limiting steps of disassembly and phase transitions of Ran-GTP-bound protein ensembles exiting nuclear pores. Chaperones also play central roles in phase transitions and proteostasis by suppressing protein aggregation. Ranbp2 haploinsufficiency promotes the age-dependent neuroprotection of the chorioretina against photo-oxidative stress by proteostatic regulations of Ranbp2 substrates and by countering the build-up of poly-ubiquitylated substrates. Further, the peptidyl-prolyl cis-trans isomerase (PPIase) and chaperone activities of the cyclophilin domain (CY) of Ranbp2 modulate the proteostasis of selective neuroprotective substrates, such as hnRNPA2B1, STAT3, HDAC4 or L/M-opsin, while promoting a decline of ubiquitylated substrates. However, links between CY PPIase activity on client substrates and its effect(s) on ubiquitylated substrates are unclear. Here, proteomics of genetically modified mice with deficits of Ranbp2 uncovered the regulation of the small heat shock chaperones - crystallins by Ranbp2 in the chorioretina. Loss of CY PPIase of Ranbp2 up-regulates αA-crystallin proteostasis, which is repressed in non-lenticular tissues. Conversely, the αA-crystallin's substrates, γ-crystallins, are down-regulated by impairment of CY's C-terminal chaperone activity. These CY-dependent effects cause the age-dependent decline of ubiquitylated substrates without overt chorioretinal morphological changes. A model emerges whereby the Ranbp2 CY-dependent remodeling of crystallins' proteostasis subdues molecular aging and preordains chorioretinal neuroprotection by augmenting the chaperone buffering capacity and the decline of ubiquitylated substrates against proteostatic impairments. Further, CY's moonlighting activity holds pan -therapeutic potential against neurodegeneration.

Pharmacokinetic Parameters of Recombinant Human Cyclophilin A in Mice

BACKGROUND AND OBJECTIVE

Cyclophilin A (CypA) is an isomerase that functions as a chaperone, housekeeping protein, and cyclosporine A (CsA) ligand. Secreted CypA is a proinflammatory factor, chemoattractant, immune regulator, and factor of antitumor immunity. Experimental data suggest clinical applications of recombinant human CypA (rhCypA) as a biotherapeutic for cancer immunotherapy, stimulation of tissue regeneration, treatment of brain pathologies, and as a supportive treatment for CsA-based therapies. The objective of this study is to analyze the pharmacokinetics of rhCypA in a mouse model.

METHODS

rhCypA was isotope-labeled with 125I and injected intraperitoneally (i.p.) or subcutaneously (s/c) into female mice as a single dose of 100 μg per mouse, equivalent to the estimated first-in-human dose. Analysis of 125I-rhCypA biodistribution and excretion was performed by direct radiometry of the blood, viscera, and urine of mice 0.5-72 h following its administration.

RESULTS

rhCypA showed rapid and even tissue-organ distribution, with the highest tropism (fT = 1.56) and accumulation (maximum concentration, Cmax = 137-167 μg/g) in the kidneys, its primary excretory organ. rhCypA showed the lowest tropism to the bone marrow and the brain (fT = 0.07) but the longest retention in these organs [mean retention time (MRT) = 25-28 h].

CONCLUSION

This study identified promising target organs for rhCypA's potential therapeutic effects. The mode of rhCypA accumulation and retention in organs could be primarily due to the expression of its receptors in them. For the first time, rhCypA was shown to cross the blood-brain barrier and accumulate in the brain. These rhCypA pharmacokinetic data could be extrapolated to humans as preliminary data for possible clinical trials.

"Cyclophilin A" Enzymatic Effect on the Aggregation Behavior of 1N4R Tau Protein: An Overlooked Crucial Determinant that should be Re-considered in Alzheimer's Disease Pathogenesis

BACKGROUND

Neurodegenerative disorders like Alzheimer's disease (AD) involve the abnormal aggregation of tau protein, which forms toxic oligomers and amyloid deposits. The structure of tau protein is influenced by the conformational states of distinct proline residues, which are regulated by peptidyl-prolyl isomerases (PPIases). However, there has been no research on the impact of human cyclophilin A (CypA) as a PPIase on (non-phosphorylated) tau protein aggregation.

METHODS

On the basis of these explanations, we used various spectroscopic techniques to explore the effects of CypA on tau protein aggregation behavior.

RESULTS

We demonstrated the role of the isomerization activity of CypA in promoting the formation of tau protein amyloid fibrils with well-defined and highly ordered cross-β structures. According to the "cistauosis hypothesis," CypA's ability to enhance tau protein fibril formation in AD is attributed to the isomerization of specific proline residues from the trans to cis configuration. To corroborate this theory, we conducted refolding experiments using lysozyme as a model protein. The presence of CypA increased lysozyme aggregation and impeded its refolding process. It is known that proper refolding of lysozyme relies on the correct (trans) isomerization of two critical proline residues.

CONCLUSION

Thus, our findings confirmed that CypA induces the trans-to-cis isomerization of specific proline residues, ultimately leading to increased aggregation. Overall, this study highlights the emerging role of isomerization in tau protein pathogenesis in AD.

Assessing Trans-Inhibition of OATP1B1 and OATP1B3 by Calcineurin and/or PPIase Inhibitors and Global Identification of OATP1B1/3-Associated Proteins

Organic anion transporting polypeptide (OATP) 1B1 and OATP1B3 are key determinants of drug-drug interactions (DDIs). Various drugs including the calcineurin inhibitor (CNI) cyclosporine A (CsA) exert preincubation-induced trans-inhibitory effects upon OATP1B1 and/or OATP1B3 (abbreviated as OATP1B1/3) by unknown mechanism(s). OATP1B1/3 are phosphoproteins; calcineurin, which dephosphorylates and regulates numerous phosphoproteins, has not previously been investigated in the context of preincubation-induced trans-inhibition of OATP1B1/3. Herein, we compare the trans-inhibitory effects exerted on OATP1B1 and OATP1B3 by CsA, the non-analogous CNI tacrolimus, and the non-CNI CsA analogue SCY-635 in transporter-overexpressing human embryonic kidney (HEK) 293 stable cell lines. Preincubation (10-60 min) with tacrolimus (1-10 µM) rapidly and significantly reduces OATP1B1- and OATP1B3-mediated transport up to 0.18 ± 0.03- and 0.20 ± 0.02-fold compared to the control, respectively. Both CsA and SCY-635 can trans-inhibit OATP1B1, with the inhibitory effects progressively increasing over a 60 min preincubation time. At each equivalent preincubation time, CsA has greater trans-inhibitory effects toward OATP1B1 than SCY-635. Preincubation with SCY-635 for 60 min yielded IC50 of 2.2 ± 1.4 µM against OATP1B1, which is ~18 fold greater than that of CsA (0.12 ± 0.04 µM). Furthermore, a proteomics-based screening for protein interactors was used to examine possible proteins and processes contributing to OATP1B1/3 regulation and preincubation-induced inhibition by CNIs and other drugs. A total of 861 and 357 proteins were identified as specifically associated with OATP1B1 and OATP1B3, respectively, including various protein kinases, ubiquitin-related enzymes, the tacrolimus (FK506)-binding proteins FKBP5 and FKBP8, and several known regulatory targets of calcineurin. The current study reports several novel findings that expand our understanding of impaired OATP1B1/3 function; these include preincubation-induced trans-inhibition of OATP1B1/3 by the CNI tacrolimus, greater preincubation-induced inhibition by CsA compared to its non-CNI analogue SCY-635, and association of OATP1B1/3 with various proteins relevant to established and candidate OATP1B1/3 regulatory processes.

Secreted cyclophilin A is non-genotoxic but acts as a tumor promoter

Chronic inflammation is associated with malignant transformation and creates the microenvironment for tumor progression. Cyclophilin A (CypA) is one of the major pro-inflammatory mediators that accumulates and persists in the site of inflammation in high doses over time. According to multiomics analyses of transformed cells, CypA is widely recognized as a pro-oncogenic factor. Vast experimental data define the functions of intracellular CypA in carcinogenesis, but findings on the role of its secreted form in tumor formation and progression are scarce. In the studies here, we exploit short-term in vitro and in vivo tests to directly evaluate the mutagenic, recombinogenic, and blastomogenic effects, as well as the promoter activity of recombinant human CypA (rhCypA), an analogue of secreted CypA. Our findings showed that rhCypA had no genotoxicity and, thus, was neither involved in nor influenced the initiation stage of carcinogenesis. At high doses, rhCypA could disrupt gap junctions in rat liver epithelial IAR-2 cells in vitro by decreasing the expression of connexins 26 and 43 in these cells and inhibit A549 cell adhesion. These data suggested that rhCypA could contribute to epithelial-mesenchymal transition in malignant cells. The research presented here elucidated the role of secreted CypA in carcinogenesis, revealing that it is not a tumor initiator but can act as a tumor promoter at high concentrations.

Proline Isomerization: From the Chemistry and Biology to Therapeutic Opportunities

Proline isomerization, the process of interconversion between the cis- and trans-forms of proline, is an important and unique post-translational modification that can affect protein folding and conformations, and ultimately regulate protein functions and biological pathways. Although impactful, the importance and prevalence of proline isomerization as a regulation mechanism in biological systems have not been fully understood or recognized. Aiming to fill gaps and bring new awareness, we attempt to provide a wholistic review on proline isomerization that firstly covers what proline isomerization is and the basic chemistry behind it. In this section, we vividly show that the cause of the unique ability of proline to adopt both cis- and trans-conformations in significant abundance is rooted from the steric hindrance of these two forms being similar, which is different from that in linear residues. We then discuss how proline isomerization was discovered historically followed by an introduction to all three types of proline isomerases and how proline isomerization plays a role in various cellular responses, such as cell cycle regulation, DNA damage repair, T-cell activation, and ion channel gating. We then explore various human diseases that have been linked to the dysregulation of proline isomerization. Finally, we wrap up with the current stage of various inhibitors developed to target proline isomerases as a strategy for therapeutic development.

Cyclophilin A as a Pro-Inflammatory Factor Exhibits Embryotoxic and Teratogenic Effects during Fetal Organogenesis

The precise balance of Th1, Th2, and Th17 cytokines is a key factor in successful pregnancy and normal embryonic development. However, to date, not all humoral factors that regulate and influence physiological pregnancy have been completely studied. Our data here pointed out cyclophilin A (CypA) as the adverse pro-inflammatory factor negatively affecting fetal development and associated with pregnancy complications. In different mouse models in vivo, we demonstrated dramatic embryotoxicity and teratogenicity of increased CypA levels during pregnancy. Using generated transgenic models, we showed that CypA overexpression in fetal tissues induced the death of all transgenic fetuses and complete miscarriage. Administration of recombinant human CypA in a high dose to pregnant females during fetal organogenesis (6.5-11.5 dpc) exhibited teratogenic effects, causing severe defects in the brain and bone development that could lead to malformations and postnatal behavioral and cognitive disorders in the offspring. Embryotoxic and teratogenic effects could be mediated by CypA-induced up-regulation of M1 macrophage polarization via activation of the STAT1/3 signaling pathways. Here, we propose secreted CypA as a novel marker of complicated pregnancy and a therapeutic target for the correction of pregnancy complications.

Uncovering new insights into the role of the ubiquitin ligase Smurf1 on the regulation of innate immune signaling and resistance to infection

Innate immunity is the body's first line of defense against infections. Innate immune cells express pattern recognition receptors in distinct cellular compartments that are responsible to detect either pathogens-associated molecules or cellular components derived from damaged cells, to trigger intracellular signaling pathways that lead to the activation of inflammatory responses. Inflammation is essential to coordinate immune cell recruitment, pathogen elimination and to keep normal tissue homeostasis. However, uncontrolled, misplaced or aberrant inflammatory responses could lead to tissue damage and drive chronic inflammatory diseases and autoimmunity. In this context, molecular mechanisms that tightly regulate the expression of molecules required for the signaling of innate immune receptors are crucial to prevent pathological immune responses. In this review, we discuss the ubiquitination process and its importance in the regulation of innate immune signaling and inflammation. Then, we summarize the roles of Smurf1, a protein that works on ubiquitination, on the regulation of innate immune signaling and antimicrobial mechanisms, emphasizing its substrates and highlighting its potential as a therapeutic target for infectious and inflammatory conditions.

Cyclophilin A associates with and regulates the activity of ZAP70 in TCR/CD3-stimulated T cells

The ZAP70 protein tyrosine kinase (PTK) couples stimulated T cell antigen receptors (TCRs) to their downstream signal transduction pathways and is sine qua non for T cell activation and differentiation. TCR engagement leads to activation-induced post-translational modifications of ZAP70, predominantly by kinases, which modulate its conformation, leading to activation of its catalytic domain. Here, we demonstrate that ZAP70 in TCR/CD3-activated mouse spleen and thymus cells, as well as human Jurkat T cells, is regulated by the peptidyl-prolyl cis-trans isomerase (PPIase), cyclophilin A (CypA) and that this regulation is abrogated by cyclosporin A (CsA), a CypA inhibitor. We found that TCR crosslinking promoted a rapid and transient, Lck-dependent association of CypA with the interdomain B region, at the ZAP70 regulatory domain. CsA inhibited CypA binding to ZAP70 and prevented the colocalization of CypA and ZAP70 at the cell membrane. In addition, imaging analyses of antigen-specific T cells stimulated by MHC-restricted antigen-fed antigen-presenting cells revealed the recruitment of ZAP70-bound CypA to the immunological synapse. Enzymatically active CypA downregulated the catalytic activity of ZAP70 in vitro, an effect that was reversed by CsA in TCR/CD3-activated normal T cells but not in CypA-deficient T cells, and further confirmed in vivo by FRET-based studies. We suggest that CypA plays a role in determining the activity of ZAP70 in TCR-engaged T cells and impact on T cell activation by intervening with the activity of multiple downstream effector molecules.

Non-Immunosuppressive Cyclophilin Inhibitors

Cyclophilins, enzymes with peptidyl-prolyl cis/trans isomerase activity, are relevant to a large variety of biological processes. The most abundant member of this enzyme family, cyclophilin A, is the cellular receptor of the immunosuppressive drug cyclosporine A (CsA). As a consequence of the pathophysiological role of cyclophilins, particularly in viral infections, there is a broad interest in cyclophilin inhibition devoid of immunosuppressive activity. This Review first gives an introduction into the physiological and pathophysiological roles of cyclophilins. The presentation of non-immunosuppressive cyclophilin inhibitors will commence with drugs based on chemical modifications of CsA. The naturally occurring macrocyclic sanglifehrins have become other lead structures for cyclophilin-inhibiting drugs. Finally, de novo designed compounds, whose structures are not derived from or inspired by natural products, will be presented. Relevant synthetic concepts will be discussed, but the focus will also be on biochemical studies, structure-activity relationships, and clinical studies.

Interleukin-2 inducible T cell kinase (ITK) may participate in the anti-bacterial immune response of Nile tilapia via regulating T-cell activation

Interleukin-2 inducible T cell kinase (ITK) plays a predominant role in the T-cell receptor (TCR) signaling cascade to ensure valid T-cell activation and function. Nevertheless, whether it regulates T-cell response of early vertebrates remains unknown. Herein, we investigated the involvement of ITK in the lymphocyte-mediated adaptive immune response, and its regulation to T-cell activation in the Nile tilapia Oreochromis niloticus. Both sequence and structure of O. niloticus ITK (OnITK) were remarkably conserved with its homologues from other vertebrates, implying its potential conserved function. OnITK mRNA was extensively expressed in lymphoid-related tissues, and with the relative highest level in peripheral blood. Once Nile tilapia was infected by Edwardsiella piscicida, OnITK in splenic lymphocytes was significantly up-regulated on 7-day post infection at both transcription and translation levels, suggesting that OnITK might involve in the primary adaptive immune response of teleost. Furthermore, upon splenic lymphocytes were stimulated by T-cell specific mitogen PHA, OnITK mRNA and protein levels were dramatically elevated. More importantly, treatment of splenic lymphocytes with specific inhibitor significantly crippled OnITK expression, which in turn impaired the inducible expression of T-cell activation markers IFN-γ, IL-2 and CD122, indicating the critical roles of ITK in regulating T-cell activation of Nile tilapia. Taken together, our results suggest that ITK takes part in the lymphocyte-mediated adaptive immunity of tilapia, and is indispensable for T-cell activation of teleost. Our findings thus provide novel evidences for understanding the mechanism regulating T-cell immunity of early vertebrates, as well as the evolution of adaptive immune system.

Reciprocal SH2-SH3 Domain Contacts between ITK Molecules Limit T Cell Receptor Signaling in Th2-type CD4+ T Cells

The nonreceptor tyrosine kinase ITK is a key component of the T cell receptor (TCR) signaling pathway and is required for cytokine production by CD4⁺ T cells that have differentiated into Th2 cells. Structural and biochemical studies suggest that contacts between the SH2 and SH3 domains of ITK mediate intermolecular self-association, forming a structure that restrains ITK activity by interfering with interactions between ITK and other components of the TCR signaling pathway. Wild-type (WT) ITK and a panel of ITK mutants containing amino acid substitutions in the SH2 and SH3 domains were tested for self-association and for binding to the adaptor protein SLP76, a key ligand for the ITK SH2 domain. WT and ITK mutants were also expressed in Itk-deficient CD4⁺ T cells via retroviral-mediated gene delivery to analyze their ability to support TCR signaling and cytokine production by Th2 cells. Specific amino acid substitutions in the ITK SH2 or SH3 domains impaired self-association, with the greatest effects being seen when both intermolecular SH2-SH3 domain contacts were disrupted. Two of the SH2 domain substitutions tested reduced ITK self-association but had no effect on binding to SLP-76. When their function was analyzed in Th2 cells, ITK proteins with diminished self-association activity supported greater IL-4 production and calcium flux in response to TCR stimulation compared to WT ITK. Our findings indicate that intermolecular contacts between ITK molecules can restrain the amplitude of TCR signaling, suggesting ITK is a limiting factor for responses by CD4+ T cells.

Delicate regulation of IL-1β-mediated inflammation by cyclophilin A

The inflammatory response is tightly regulated, but its regulatory principles are still incompletely understood. Cyclophilin A (CypA) has long been considered as a pro-inflammatory factor. Here, we discover how CypA precisely regulates interleukin-1β (IL-1β)-mediated inflammatory responses. In lipopolysaccharide-treated mice, CypA deficiency initially inhibits and then promotes lung inflammation, which is closely related to IL-1β production. Mechanistically, CypA not only facilitates pro-IL-1β processing by increasing Smurf1-mediated K63-linked ubiquitination in an ATP-dependent manner but also accelerates pro-IL-1β degradation, depending on Smurf1-mediated K48-linked ubiquitination. Moreover, in IL-1β-treated mice, CypA exacerbates lung injury by enhancing cytokine production. It also upregulates the ILK/AKT pathway by inhibiting Cyld-mediated K63-linked ILK deubiquitination, which promotes the epithelial-mesenchymal transition (EMT) to facilitate lung repair. Collectively, CypA promotes inflammation activation by increasing IL-1β production and then promotes inflammation resolution by enhancing redundant pro-IL-1β degradation and IL-1β-induced EMT, indicating the complex and delicate regulation of inflammatory response.

Preparative Production and Purification of Recombinant Human Cyclophilin A

In this work, we developed the method of preparative production of recombinant human cyclophilin A (rhCypA) in Escherichia coli. The full-length cDNA encoding the gene of human CypA (CYPA) was amplified by RT-PCR from the total RNA of human T cell lymphoma Jurkat. The nucleotide sequence of CYPA was optimized to provide highly effective translation in E. coli. Recombinant CYPA DNA was cloned into the pET22b(+) vector, and the resulted expression plasmid was used to transform E. coli strain BL21(DE3)Gold. The recombinant producer strain of E. coli produced soluble rhCypA in the bacterial cytoplasm. The synthesis efficiency of rhCypA was up to 50% of the total cell protein allowing to produce rhCypA in the amount of 1 g per liter of the culture. We also developed the method for rhCypA purification, consisting of a single-step tandem anion exchange chromatography on DEAE- and Q-Sepharose columns. The protein purity was 95% according to electrophoresis (SDS-PAGE), and its contamination with endotoxin did not exceed 0.05 ng per 1 mg of the protein that met the requirements of European pharmacopoeia for injectable preparations. The produced recombinant protein exhibited functional features of native CypA, i.e., isomerase activity and chemokine activity as assessed by stimulation of migration of mouse bone marrow hematopoietic stem cells in vivo. The generated producer strain of E. coli is a super-producer and could be used for large-scale experimental studies of rhCypA and in its preclinical and clinical trials as a drug.

Defective cyclophilin A induces TDP-43 proteinopathy: implications for amyotrophic lateral sclerosis and frontotemporal dementia

Aggregation and cytoplasmic mislocalization of TDP-43 are pathological hallmarks of amyotrophic lateral sclerosis and frontotemporal dementia spectrum. However, the molecular mechanism by which TDP-43 aggregates form and cause neurodegeneration remains poorly understood. Cyclophilin A, also known as peptidyl-prolyl cis-trans isomerase A (PPIA), is a foldase and molecular chaperone. We previously found that PPIA interacts with TDP-43 and governs some of its functions, and its deficiency accelerates disease in a mouse model of amyotrophic lateral sclerosis.

Here we characterized PPIA knock-out mice throughout their lifespan and found that they develop a neurodegenerative disease with key behavioural features of frontotemporal dementia, marked TDP-43 pathology and late-onset motor dysfunction.

In the mouse brain, deficient PPIA induces mislocalization and aggregation of the GTP-binding nuclear protein Ran, a PPIA interactor and a master regulator of nucleocytoplasmic transport, also for TDP-43. Moreover, in absence of PPIA, TDP-43 autoregulation is perturbed and TDP-43 and proteins involved in synaptic function are downregulated, leading to impairment of synaptic plasticity. Finally, we found that PPIA was downregulated in several patients with amyotrophic lateral sclerosis and amyotrophic lateral sclerosis-frontotemporal dementia, and identified a PPIA loss-of-function mutation in a patient with sporadic amyotrophic lateral sclerosis . The mutant PPIA has low stability, altered structure and impaired interaction with TDP-43.

These findings strongly implicate that defective PPIA function causes TDP-43 mislocalization and dysfunction and should be considered in future therapeutic approaches.

Cyclophilin A regulates A549 cells apoptosis via stabilizing Twist1 protein

Cyclophilin A (CypA) is an essential member of the immunophilin family. As an intracellular target of immunosuppressive drug cyclosporin A (CsA) or a peptidyl-prolyl cis/trans isomerase (PPIase), it catalyzes the cis-trans isomerization of proline amidic peptide bonds, through which, it regulates a variety of biological processes, such as intracellular signaling, transcription, and apoptosis. In this study, we found that intracellular CypA enhanced Twist1 phosphorylation at Ser68 and inhibited apoptosis in A549 cells. Mechanistically, CypA could mediate the phosphorylation of Twist1 at Ser68 via p38 MAPK, which inhibited its ubiquitination-mediated degradation. In addition, CypA increased Twist-p65 interaction and nuclear accumulation, which regulated Twist1-dependent expression of CDH1 and CDH2. Our findings collectively indicated the role of CypA in Twist1-mediated A549 cells apoptosis through stabilizing Twist1 protein.

Targeting of the Tec Kinase ITK Drives Resolution of T Cell-Mediated Colitis and Emerges as Potential Therapeutic Option in Ulcerative Colitis

BACKGROUND & AIMS

The molecular checkpoints driving T cell activation and cytokine responses in ulcerative colitis (UC) are incompletely understood. Here, we studied the Tec kinase ITK in UC.

METHODS

We analyzed patients with inflammatory bowel disease (n = 223) and evaluated ITK activity as well as the functional effects of cyclosporine-A (CsA). In addition, 3 independent murine colitis models were used to investigate the functional role of ITK. Finally, the activity of ITK was blocked via pharmacological inhibitors and genetically engineered mice. Readout parameters were mini-endoscopy, histopathology, mucosal T cell apoptosis, and cytokine production.

RESULTS

We found an expansion of pITK-expressing mucosal CD4+ T cells in UC rather than Crohn's disease that correlated with disease severity. CsA suppressed activation of ITK in cultured CD4+ T cells and calcineurin-containing microclusters adjacent to the T cell receptor signaling complex. Functionally, the capacity of CsA to suppress activity of experimental colitis was critically dependent on ITK. Genetic inactivation of Itk via gene targeting or induction of allele-sensitive Itk mutants prevented experimental colitis in 3 colitis models, and treatment with pharmacological ITK blockers suppressed established colitis. In addition, ITK controlled apoptosis and activation of mucosal Th2 and Th17 lymphocytes via NFATc2 signaling pathways.

CONCLUSIONS

ITK activation was detected in UC and could be down-regulated in cultured T cells by CsA administration. Selective targeting of ITK emerges as an attractive approach for treatment of chronic intestinal inflammation and potentially UC by driving resolution of mucosal inflammation.

Cyclophilin A Inhibits Human Respiratory Syncytial Virus (RSV) Replication by Binding to RSV-N through Its PPIase Activity

Human respiratory syncytial virus (hRSV) is the most common pathogen which causes acute lower respiratory infection (ALRI) in infants. Recently, virus-host interaction has become a hot spot of virus-related research, and it needs to be further elaborated for RSV infection. In this study, we found that RSV infection significantly increased the expression of cyclophilin A (cypA) in clinical patients, mice, and epithelial cells. Therefore, we evaluated the function of cypA in RSV replication and demonstrated that virus proliferation was accelerated in cypA knockdown host cells but restrained in cypA-overexpressing host cells. Furthermore, we proved that cypA limited RSV replication depending on its PPIase activity. Moreover, we performed liquid chromatography-mass spectrometry, and the results showed that cypA could interact with several viral proteins, such as RSV-N, RSV-P, and RSV-M2-1. Finally, the interaction between cypA and RSV-N was certified by coimmunoprecipitation and immunofluorescence. Those results provided strong evidence that cypA may play an inhibitory role in RSV replication through interaction with RSV-N via its PPIase activity.

IMPORTANCE RSV-N, packed in the viral genome to form the ribonucleoprotein (RNP) complex, which is recognized by the RSV RNA-dependent RNA polymerase (RdRp) complex to initiate viral replication and transcription, plays an indispensable role in the viral biosynthesis process. cypA, binding to RSV-N, may impair this function by weakening the interaction between RSV-N and RSV-P, thus leading to decreased viral production. Our research provides novel insight into cypA antiviral function, including binding to viral capsid protein to inhibit viral replication, which may be helpful for new antiviral drug exploration.

Porphyromonas gingivalis lipopolysaccharide and gingival fibroblast augment MMP-9 expression of monocytic U937 cells through cyclophilin A

BACKGROUND

Intercellular cross-talking was suggested in matrix metalloproteinase (MMP)-9 expression with unknown mechanisms. Studies showed cyclophilin A (CypA) playing an important role in regulating MMP-9 expression in varied diseases. The aim of the study was to examine the CyPA on the MMP-9 augmentation in monocytic U937 cells after Porphyromonas gingivalis (Pg) lipopolysaccharide (LPS) treatment and human gingival fibroblast (hGF) co-culture.

METHODS

In independent culture or co-culture of hGF and U937 cell, quantitative real-time polymerase chain reaction (qPCR) and zymography were selected to examine the mRNA and protein activity of MMP-9, respectively. The CyPA expression was determined by qPCR.

RESULTS

LPS could enhance MMP-9 mRNA expression and enzyme activity in U937 cell. However, the enhancements were not observed in hGF. Similarly, LPS enhanced CyPA mRNA in U937, but not in hGF. After co-cultured with hGF, however, MMP-9 and CyPA in U937 increased regardless of the presence/absence of LPS. In U937 cells, the extra-supplied CyPA increased MMP-9 mRNA and enzyme activity, whereas the CyPA inhibitor, cyclosporine A, suppressed the LPS- and co-culture-enhanced MMP-9. Moreover, the inhibitors for MAP kinase, including PD98059 (ERK) and SP600125 (JNK), suppressed the CyPA-enhanced MMP-9 in U937.

CONCLUSION

Through the CyPA pathway, the LPS and the hGF could augment the MMP-9 expression in the U937 cells.

Cyclophilin A Plays Potential Roles in a Rat Model of Asthma and Suppression of Immune Response

Purpose

Cyclophilin A (CypA) inhibits CD4⁺ T cell signal transduction via interleukin-2-inducible T-cell kinase (Itk), a tyrosine kinase required for T helper (Th) 2 cells function. Furthermore, mice with CypA silencing developed allergic diseases associated with increased Th2 cytokines production. CD4⁺ T cells with a Th2-cytokine pattern have been demonstrated to have a pivotal role in the pathogenesis of asthma. However, the effects of CypA in regulating immunity in asthma and in relieving asthmatic symptoms in vivo are entirely unknown.

Methods

Recombinant CypA protein (rCypA) was generated and purified. Ovalbumin (OVA)-challenged asthmatic rats model and acetylcholine chloride (ACh)-induced contraction of tracheal spirals were established. The pulmonary resistance (RL) value of asthmatic rats in vivo and the isometric tension of tracheal spirals ex vivo were recorded by MFLab 3.01 software. The levels of Th1 and Th2 cytokines and the quantities of immunoglobulin (IgA, IgG, IgM and IgE) in the supernatants of rat spleen lymphocytes were detected and analysed by bio-plex Suspension Array System and ELISA, respectively. CD4⁺ T cells were separated by MicroBeads, and the levels of interleukin (IL)-4 and interferon-γ (IFN-γ) were detected by ELISA.

Results

rCypA (10 ng/kg) significantly reduced RL within 2–7 min in OVA-challenged asthmatic rats in vivo, and there were no significant differences compared with terbutaline (TB) and hydrocortisone (HC). Furthermore, rCypA (10 ng/mL) significantly reduced the isometric tension in the ACh-induced contraction of the tracheal spiral ex vivo, and the effect of rCypA was better than that of TB. Additionally, rCypA suppressed the secretion of both Th1 and Th2 cytokines, and the suppressive effects of rCypA were stronger than those of HC, especially on Th2 cytokines.

Conclusion

These findings indicate that CypA may serve as a potential novel therapeutic strategy for asthma.

Host factor cyclophilin B affects Orf virus replication by interacting with viral ORF058 protein

Poxviruses have evolved multiple strategies to modulate host-derived factors to create an optimal environment for viral efficient replication. Our previous study indicated that cyclophilin B (CypB) is a critical factor for ORFV replication in MDBK cells. However, the precise molecular mechanism by which CypB facilitates ORFV replication remains less understood. In the present study, the function of CypB in ORFV replication is further evaluated. The overexpression of CypB was observed to facilitate ORFV replication in OFTu cells and HeLa cells, however, RNA interference (RNAi)-mediated reduction of endogenous CypB decreased the levels of ORFV replication. Coimmunoprecipitation experiments revealed that the CypB interacted with ORFV ORF058 protein, a late protein involved in virus entry. The interaction of host factor CypB and ORF058 protein was further confirmed by confocal microscopy analysis and GST-pull down. In addition, the 52-55 aa was identified as the critical binding sites for CypB on ORF058 protein by GST-pull down with OFTu cells overexpressing CypB and purified GST-tagged truncated ORF058. In conclusion, we demonstrate that CypB is a critical host factor for ORFV replication in vitro by interacting with ORF058 protein, providing new insights into ORFV pathogenesis.

Cyclophilin A is a factor of antitumor defense in the early stages of tumor development

Cyclophilin A (CypA) is a pro-inflammatory factor with multiple immunomodulating effects. Here, we investigated the effects of recombinant human CypA (rhCypA) as a factor of antitumor host defense. Our results demonstrated that rhCypA dramatically inhibited the growth of murine transplantable tumors (mammary adenocarcinoma Ca755, melanoma B16, Lewis lung carcinoma (LLC), and cervical cancer CC-5). In the B16 model, rhCypA effects were observed only when tumor cells were transplanted at the significantly reduced injection dose, indicating that antitumor properties of rhCypA are more effective at the initial stages of cancer development. Antitumor effect of rhCypA in the CC-5 model was comparable to the action of 5-fluorouracil (5FU), and rhCypA administration prevented 5FU - induced leukopenia in the blood of tumor-bearing mice. In the LLC model, rhCypA injection before but not after tumor resection significantly suppressed the formation of post-surgical metastases. RhCypA exhibited no direct cytotoxic effects in vitro on human leukemia cells (K-562, HL-60, KG-1), indicating that rhCypA antitumor action could be mediated by its immunomodulating activity. In the B16 model, rhCypA had no impact on tumor angiogenesis and gene expression of several MMPs, endogenous CypA, and CD147, which play a crucial role in cancer progression. However, in this model, rhCypA stimulated gene expression of MMPs 8, 9, and 12 that could contribute to malignancy growth inhibition. Here, our findings pointed out CypA as one of the factors of antitumor host defense that can effectively control the initial stages of tumor and metastases formation by regulating the action of MMPs and changing the tumor microenvironment.

Induction of cyclophilin A by influenza A virus infection facilitates group A Streptococcus coinfection

During influenza A epidemics, bacterial coinfection is a major cause of increased morbidity and mortality. However, the roles of host factors in regulating influenza A virus (IAV)-triggered bacterial coinfection remain elusive. Cyclophilin A (CypA) is an important regulator of infection and immunity. Here, we show that IAV-induced CypA expression facilitates group A Streptococcus (GAS) coinfection both in vitro and in vivo. Upon IAV infection, CypA interacts with focal adhesion kinase (FAK) and inhibited E3 ligase cCbl-mediated, K48-linked ubiquitination of FAK, which positively regulates integrin α5 expression and actin rearrangement via the FAK/Akt signaling pathway to facilitate GAS colonization and invasion. Notably, CypA deficiency or inhibition by cyclosporine A significantly inhibits IAV-triggered GAS coinfection in mice. Collectively, these findings reveal that CypA is critical for GAS infection, and induction of CypA expression is another way for IAV to promote bacterial coinfection, suggesting that CypA is a promising therapeutic target for the secondary bacterial infection.

MicroRNAs as the critical regulators of Doxorubicin resistance in breast tumor cells

BACKGROUND

Chemotherapy is one of the most common treatment options for breast cancer (BC) patients. However, about half of the BC patients are chemotherapeutic resistant. Doxorubicin (DOX) is considered as one of the first line drugs in the treatment of BC patients whose function is negatively affected by multi drug resistance. Due to the severe side effects of DOX, it is very important to diagnose the DOX resistant BC patients. Therefore, assessment of molecular mechanisms involved in DOX resistance can improve the clinical outcomes in BC patients by introducing the novel therapeutic and diagnostic molecular markers. MicroRNAs (miRNAs) as members of the non-coding RNAs family have pivotal roles in various cellular processes including cell proliferation and apoptosis. Therefore, aberrant miRNAs functions and expressions can be associated with tumor progression, metastasis, and drug resistance. Moreover, due to miRNAs stability in body fluids, they can be considered as non-invasive diagnostic markers for the DOX response in BC patients.

MAIN BODY

In the present review, we have summarized all of the miRNAs that have been reported to be associated with DOX resistance in BC for the first time in the world.

CONCLUSIONS

Since, DOX has severe side effects; it is required to distinguish the non DOX-responders from responders to improve the clinical outcomes of BC patients. This review highlights the miRNAs as pivotal regulators of DOX resistance in breast tumor cells. Moreover, the present review paves the way of introducing a non-invasive panel of prediction markers for DOX response among BC patients.

The regulatory function of mixed lineage kinase 3 in tumor and host immunity

Protein kinases are the second most sought-after G-protein coupled receptors as drug targets because of their overexpression, mutations, and dysregulated catalytic activities in various pathological conditions. Till 2019, 48 protein kinase inhibitors have received FDA approval for the treatment of multiple illnesses, of which the majority of them are indicated for different malignancies. One of the attractive sub-group of protein kinases that has attracted attention for drug development is the family members of MAPKs that are recognized to play significant roles in different cancers. Several inhibitors have been developed against various MAPK members; however, none of them as monotherapy has shown sustainable efficacy. One of the MAPK members, called Mixed Lineage Kinase 3 (MLK3), has attracted considerable attention due to its role in inflammation and neurodegenerative diseases; however, its role in cancer is an emerging area that needs more investigation. Recent advances have shown that MLK3 plays a role in cancer cell survival, migration, drug resistance, cell death, and tumor immunity. This review describes how MLK3 regulates different MAPK pathways, cancer cell growth and survival, apoptosis, and host's immunity. We also discuss how MLK3 inhibitors can potentially be used along with immunotherapy for different malignancies.

Urinary Cyclophilin A as Marker of Tubular Cell Death and Kidney Injury

Background: Despite the term acute kidney injury (AKI), clinical biomarkers for AKI reflect function rather than injury and independent markers of injury are needed. Tubular cell death, including necroptotic cell death, is a key feature of AKI. Cyclophilin A (CypA) is an intracellular protein that has been reported to be released during necroptosis. We have now explored CypA as a potential marker for kidney injury in cultured tubular cells and in clinical settings of ischemia-reperfusion injury (IRI), characterized by limitations of current diagnostic criteria for AKI. Methods: CypA was analyzed in cultured human and murine proximal tubular epithelial cells exposed to chemical hypoxia, hypoxia/reoxygenation (H/R) or other cell death (apoptosis, necroptosis, ferroptosis) inducers. Urinary levels of CypA (uCypA) were analyzed in patients after nephron sparing surgery (NSS) in which the contralateral kidney is not disturbed and kidney grafts with initial function. Results: Intracellular CypA remained unchanged while supernatant CypA increased in parallel to cell death induction. uCypA levels were higher in NSS patients with renal artery clamping (that is, with NSS-IRI) than in no clamping (NSS-no IRI), and in kidney transplantation (KT) recipients (KT-IRI) even in the presence of preserved or improving kidney function, while this was not the case for urinary Neutrophil gelatinase-associated lipocalin (NGAL). Furthermore, higher uCypA levels in NSS patients were associated with longer surgery duration and the incidence of AKI increased from 10% when using serum creatinine (sCr) or urinary output criteria to 36% when using high uCypA levels in NNS clamping patients. Conclusions: CypA is released by kidney tubular cells during different forms of cell death, and uCypA increased during IRI-induced clinical kidney injury independently from kidney function parameters. Thus, uCypA is a potential biomarker of kidney injury, which is independent from decreased kidney function.

Reconstitution of a functional human thymus by postnatal stromal progenitor cells and natural whole-organ scaffolds

The thymus is a primary lymphoid organ, essential for T cell maturation and selection. There has been long-standing interest in processes underpinning thymus generation and the potential to manipulate it clinically, because alterations of thymus development or function can result in severe immunodeficiency and autoimmunity. Here, we identify epithelial-mesenchymal hybrid cells, capable of long-term expansion in vitro, and able to reconstitute an anatomic phenocopy of the native thymus, when combined with thymic interstitial cells and a natural decellularised extracellular matrix (ECM) obtained by whole thymus perfusion. This anatomical human thymus reconstruction is functional, as judged by its capacity to support mature T cell development in vivo after transplantation into humanised immunodeficient mice. These findings establish a basis for dissecting the cellular and molecular crosstalk between stroma, ECM and thymocytes, and offer practical prospects for treating congenital and acquired immunological diseases.

TCR Signal Strength and Antigen Affinity Regulate CD8+ Memory T Cells

CD8⁺ T cells play a critical role in adaptive immunity, differentiating into CD8⁺ memory T cells that form the basis of protective cellular immunity. Vaccine efficacy is attributed to long-term protective immunity, and understanding the parameters that regulate development of CD8⁺ T cells is critical to the design of T cell-mediated vaccines. We show in this study using mouse models that two distinct parameters, TCR signal strength (regulated by the tyrosine kinase ITK) and Ag affinity, play important but separate roles in modulating the development of memory CD8⁺ T cells. Unexpectedly, our data reveal that reducing TCR signal strength along with reducing Ag affinity for the TCR leads to enhanced and accelerated development of CD8⁺ memory T cells. Additionally, TCR signal strength is able to regulate CD8⁺ T cell effector cytokine R production independent of TCR Ag affinity. Analysis of RNA-sequencing data reveals that genes for inflammatory cytokines/cytokine receptors are significantly altered upon changes in Ag affinity and TCR signal strength. Furthermore, our findings show that the inflammatory milieu is critical in regulating this TCR signal strength-mediated increase in memory development, as both CpG oligonucleotide treatment or cotransfer of wild-type and Itk^-/- T cells eliminates the observed increase in memory cell formation. These findings suggest that TCR signal strength and Ag affinity independently contribute to CD8⁺ memory T cell development, which is modulated by inflammation, and suggest that manipulating TCR signal strength along with Ag affinity, may be used to tune the development of CD8⁺ memory T cells during vaccine development.

Fibroblast-enhanced cyclophilin A releasing from U937 cell upregulates MMP-2 in gingival fibroblast

OBJECTIVE

This in vitro study aimed to evaluate the expression of cyclophilin A (CyPA) in U937 monocytic cells after coculturing with the human gingival fibroblasts (HGFs) and the effect of CyPA on the augmentation of MMP-2 expression in the coculture environment.

BACKGROUND

Leukocyte infiltration in gingival connective tissue is one of the major findings in the lesions of inflammatory periodontal diseases. A crosstalk between the resident gingival fibroblasts and the recruited inflammatory cells that promote the expression of matrix metalloproteinases (MMPs) was proposed based on recent findings, whereas the cluster of differentiation 147 (CD147)-CyPA pathway was suggested to be involved with the crosstalk.

MATERIAL AND METHODS

CyPA was released into media, in the independent or transwell coculture of HGF and U937 cells, as determined by enzyme-linked immunosorbent assay, whereas intracellular mRNA expressions for CyPA and MMP-2 were examined by quantitative real-time polymerase chain reaction, in the transwell coculture or conditional medium models. Zymography was conducted to analyze the activities of pro-MMP-2/MMP-2 released into the media.

RESULTS

(a) A significantly increased CyPA protein level was observed in the transwell coculture media compared with that in the independent culture. (b) The transwell coculture-enhanced mRNA expression for CyPA was noticed in U937 cells but not in HGFs. After adding with HGF-conditioned medium, the mRNA enhancement in U937 cells occurred in a dose-dependent manner. (c) Although the MMP-2 activities significantly increased after transwell coculturing, the MMP-2 mRNA enhancement was observed only in HGFs. (d) Exogenous CyPA could enhance MMP-2 activities in HGFs in a dose-dependent manner. However, the CyPA antagonist reduced the MMP-2 activities in the transwell cocultures. (e) Moreover, the CyPA-enhanced MMP-2 activity in HGF was decreased significantly by the pathway inhibitor for c-Jun amino-terminal kinase (JNK).

CONCLUSION

Based on the present findings, we suggest that gingival fibroblasts could enhance the CyPA release from U937 cells, via the JNK pathway, resulting in MMP-2 enhancement in fibroblasts. The finding shed light on a new mechanism of cellular interaction involving MMP-2 and CyPA, in two cells.

Mixed lineage kinase 3 inhibition induces T cell activation and cytotoxicity

Mixed lineage kinase 3 (MLK3), also known as MAP3K11, was initially identified in a megakaryocytic cell line and is an emerging therapeutic target in cancer, yet its role in immune cells is not known. Here, we report that loss or pharmacological inhibition of MLK3 promotes activation and cytotoxicity of T cells. MLK3 is abundantly expressed in T cells, and its loss alters serum chemokines, cytokines, and CD28 protein expression on T cells and its subsets. MLK3 loss or pharmacological inhibition induces activation of T cells in in vitro, ex vivo, and in vivo conditions, irrespective of T cell activating agents. Conversely, overexpression of MLK3 decreases T cell activation. Mechanistically, loss or inhibition of MLK3 down-regulates expression of a prolyl-isomerase, Ppia, which is directly phosphorylated by MLK3 to increase its isomerase activity. Moreover, MLK3 also phosphorylates nuclear factor of activated T cells 1 (NFATc1) and regulates its nuclear translocation via interaction with Ppia, and this regulates T cell effector function. In an immune-competent mouse model of breast cancer, MLK3 inhibitor increases Granzyme B-positive CD8+ T cells and decreases MLK3 and Ppia gene expression in tumor-infiltrating T cells. Likewise, the MLK3 inhibitor in pan T cells, isolated from breast cancer patients, also increases cytotoxic CD8+ T cells. These results collectively demonstrate that MLK3 plays an important role in T cell biology, and targeting MLK3 could serve as a potential therapeutic intervention via increasing T cell cytotoxicity in cancer.

Analyses of the toxic properties of recombinant human Cyclophilin A in mice

Cyclophilin A (CypA), an 18 kDa multi-functional protein with cis-trans isomerase activity, is both a ligand for cyclosporine A and a proinflammatory factor. CypA is also a chemoattractant for hemopoietic stem cells and progenitors of different lineages, and can mediate regenerative processes in an organism. Accumulated experimental data have suggested there are practical applications for this protein in the treatment of several diseases (i.e. neutralization of cyclosporine A side effects, etc.). However, the range of CypA safe doses as well as its toxic effects remain unknown. The study here investigated the acute toxicity of a single intraperitoneal (IP) or subcutaneous (SC) dosing of recombinant human CypA (rhCypA) in both female and male mice and its effect on gene expression of acute phase proteins (APP) in the female mice after IP treatment. The results showed that toxicity of rhCypA was most evident in female and male mice dosed IP with 750 mg/kg, and manifested as kidney injury and increased granulocyte/lymphocyte ratios in the blood. Enhanced expression of Sаа1 and Sаа2 genes was induced with doses of 0.1-2 mg/mouse of rhCypA. Injection of the maximal dose (750 mg/kg) significantly stimulated expression of all the APP genes studied.

A cyclophilin A (CypA) from Apostichopus japonicus modulates NF-κB translocation as a cofactor

As a ubiquitously expressed protein, cyclophilin A (CypA) is involved in a variety of pathological process, including immune suppression, inflammation, cell apoptosis, viral infection and stress response. However, the functional roles of CypA were largely unknown in economic marine animals. In this report, a novel CypA gene from sea cucumber Apostichopus japonicus (designated as AjCypA) was cloned and its function roles in immune responses were explored. The full-length cDNA of AjCypA was 1297 bp containing an open reading frame of 489 bp encoding a putative protein of 162 amino acids (aa). A conserved cyclophilin-like domain (CLD) with PPIase signature was located from 5 to 155 aa sequences in AjCypA, in which five necessary aa residues was totally conserved. In healthy sea cucumbers, AjCypA was expressed in all detected tissues, with highly expressed in muscles and weakly expressed in coelomocytes. AjCypA transcripts was significantly induced 8.08-fold and 5.65-fold in coelomocytes when sea cucumbers challenged with Vibrio splendidus in vivo and LPS in vitro, respectively. The expression pattern is similar with the expression of AjRel in the same condition. Moreover, GST pull-down and immunofluorescence analysis both revealed that AjCypA might be interacted with AjRel. Furthermore, AjCypA knockdown not only inhibited the expression of inflammation cytokines, but also suppressed the translocation of AjRel in nucleus induced by LPS. Taken together, our results suggested that AjCypA play key roles in V. splendidus mediated immune responses via suppressing the nuclear translocation of AjRel activity in sea cucumber.

The contribution of cyclophilin A to immune-mediated central nervous system inflammation

Cyclophilin A has multiple known functions in inflammation. Intracellular cyclophilin A modulates T helper 2 response (Th2) and extracellular cyclophilin A functions as a leukocyte chemotactic factor. The contribution of cyclophilin A to central nervous system (CNS) inflammation has not been reported. To test the hypothesis that inhibition of cyclophilin A would ameliorate immune-mediated CNS inflammation, we compared the course and neuroimmunology of experimental allergic encephalomyelitis (EAE) in cyclophilin A knockout mice and wild type littermates. There was a trend towards lower incidence of EAE in cyclophilin A knockout mice, but the clinical course of EAE among animals that manifested clinical signs of EAE was similar in cyclophilin A knockout and wild type littermates. Antigen recall response to myelin oligodendrocyte glycoprotein (MOG) peptide showed that interferon-γ release was lower in cyclophilin A knockout mice. Analysis of CNS inflammatory cells showed that CD3+ T cell infiltration into the CNS was lower in cyclophilin A knockout mice. These results showed that the loss of cyclophilin A results in altered peripheral immune activation and CNS leukocyte infiltration, but these changes did not result in a substantial change in the clinical course of EAE.

Cyclophilin a signaling induces pericyte-associated blood-brain barrier disruption after subarachnoid hemorrhage

Objective

The potential roles and mechanisms of pericytes in maintaining blood–brain barrier (BBB) integrity, which would be helpful for the development of therapeutic strategies for subarachnoid hemorrhage (SAH), remain unclear. We sought to provide evidence on the potential role of pericytes in BBB disruption and possible involvement and mechanism of CypA signaling in both cultured pericytes and SAH models.

Methods

Three hundred fifty-three adult male C57B6J mice weighing 22 to 30 g, 29 CypA^−/− mice, 30 CypA^+/+ (flox/flox) mice, and 30 male neonatal C57B6J mice were used to investigate the time course of CypA expression in pericytes after SAH, the intrinsic function and mechanism of CypA in pericytes, and whether the known receptor CD147 mediates these effects.

Results

Our data demonstrated both intracellular CypA and CypA secretion increased after SAH and could activate CD147 receptor and downstream NF-κB pathway to induce MMP9 expression and proteolytic functions for degradation of endothelium tight junction proteins and basal membranes. CypA served as autocrine or paracrine ligand for its receptor, CD147. Although CypA could be endocytosed by pericytes, specific endocytosis inhibitor chlorpromazine did not have any effect on MMP9 activation. However, specific knockdown of CD147 could reverse the harmful effects of CypA expression in pericytes on the BBB integrity after SAH.

Conclusions

This study demonstrated for the first time that CypA mediated the harmful effects of pericytes on BBB disruption after SAH, which potentially mediated by CD147/NF-κB/MMP9 signal, and junction protein degradation in the brain. By targeting CypA and pericytes, this study may provide new insights on the management of SAH patients.

Cyclophilin A protects HIV-1 from restriction by human TRIM5α

The HIV-1 capsid (CA) protein lattice encases viral genomic RNA and regulates steps essential to target cell invasion¹. Cyclophilin A (CypA) has interacted with the CA of lentiviruses related to HIV-1 for millions of years^2–7. Disruption of the CA-CypA interaction decreases HIV-1 infectivity in human cells^8–12, but stimulates infectivity in non-human primate cells^13–15. Genetic and biochemical data suggest that CypA protects HIV-1 from a CA-specific restriction factor in human cells^16–20. Discovery of the CA-specific restriction factor tripartite-containing motif 5α (TRIM5α)²¹, and of multiple, independently-derived, TRIM5-CypA fusion genes^{4,5,15,22–26}, pointed to human TRIM5α as the CypA-sensitive restriction factor. However, HIV-1 restriction by human TRIM5α in tumor cell lines is minimal²¹, and inhibition of such activity by CypA has not been detected²⁷. Here, exploiting reverse genetic tools optimized for primary human blood cells, we demonstrate that disruption of the CA-CypA interaction renders HIV-1 susceptible to potent restriction by human TRIM5α, with the block occurring before reverse transcription. Endogenous TRIM5α associated with virion cores as they entered the cytoplasm, but only when the CA-CypA interaction was disrupted. These experiments resolve the long-standing mystery of the role of CypA in HIV-1 replication by demonstrating that this ubiquitous cellular protein shields HIV-1 from previously inapparent restriction by human TRIM5α.

Cyclophilin Inhibitor NV556 Reduces Fibrosis and Hepatocellular Carcinoma Development in Mice With Non-Alcoholic Steatohepatitis

Hepatocellular carcinoma (HCC), the third major cause of cancer mortality, can result from non-alcoholic steatohepatitis (NASH). Due to limited efficacy of drugs approved for HCC and no drug available yet for NASH, identification of new effective treatments is crucial. Here, we investigated whether NV556, a cyclophilin inhibitor derived from sanglifehrins, would decrease the development of NASH and HCC in a preclinical mouse model. For our experiment, male mice were administered streptozotocin to disrupt pancreatic cells and nourished with high-fat diet since 3 weeks of age. Afterward, NV556 or vehicle was orally administered daily for 6 weeks before the 14-week-old time point for the development of NASH, or 10 weeks before the 30-week-old time point for the establishment of HCC. Body weight, blood glucose level, and liver weight were recorded. Moreover, for NASH, livers were histologically examined for inflammation and steatosis. Collagen was measured by Sirius Red staining of hepatic tissues. Systemic cytokine levels in serum were detected by multiplex assays. For HCC, nodules of livers were measured and scored according to a developed system with number and size of nodules as criteria. NV556 significantly decreased collagen deposition (p = 0.0281), but did not alter inflammation, steatosis, body and liver weight, and systemic cytokine production compared to control mice with NASH symptoms. For HCC, NV556 statistically reduced the number (p = 0.0091) and diameter of tumorous nodules (p = 0.0264), along with liver weight (p = 0.0026) of mice.Our study suggests NV556 as a promising candidate for treatment of NASH-derived fibrosis and HCC.

STAT3-CyPA signaling pathway in endothelial cell apoptosis

Cyclophilin A (CyPA), which is encoded by PPIA, is a ubiquitously expressed intracellular protein and is secreted in response to inflammatory stimuli. CyPA stimulates proinflammatory and apoptosis signaling pathways in vascular smooth muscle cells (VSMCs) and endothelial cells (ECs), promotes VSMC migration and proliferation, EC adhesion molecules expression, and inflammatory cell chemotaxis and apoptosis. Therefore, we sought to study the transcriptional regulation of CyPA, we hypothesized that transcription factor STAT3 regulated CyPA expression and activated vascular ECs in vitro in a CyPA-dependent manner. Using RT-qPCR, immunostaining, luciferase and ChIP assays, we found that STAT3 induced CyPA expression depended on its transcriptional activation by binding to a specific region containing the STAT3-responsive element (SRE) in the CyPA promoter. Moreover, with cell viability and apoptosis assays, we identified STAT3 stimulated CyPA-dependent apoptosis of human umbilical vein ECs in vitro.

Cyclophillin A deficiency accelerates RML-induced prion disease

Prion diseases typically involve brain deposition of abnormally folded prion protein, which is associated with activated glia and increased cytokine production. Cyclophilin A (CypA) is a ubiquitous protein with peptidyl prolyl cis-trans isomerase activity, which regulates protein folding, and can be secreted by cells in response to inflammatory stimuli. On the basis of in vitro studies, CypA was proposed to mediate glial activation during prion infection. To investigate the role of CypA in vivo, we inoculated CypA^+/+, CypA^+/- and CypA^-/- mice with the RML prion strain, and recorded the time to onset of neurological signs and to terminal disease, and the astrocyte and microglia response at presymptomatic and symptomatic stages. Time to onset of disease and survival were significantly shorter in CypA-deficient mice than CypA-expressing controls. CypA-deficient mice had significantly greater microglial activation in the presymptomatic stage, and analysis of anti- and pro-inflammatory microglial markers indicated a shift towards a pro-inflammatory phenotype. There was no difference in astrocyte activation. This suggests that CypA contributes to dampening the pro-inflammatory microglial response during the early stage of RML-induced prion disease.

Cyclophilin A Function in Mammary Epithelium Impacts Jak2/Stat5 Signaling, Morphogenesis, Differentiation, and Tumorigenesis in the Mammary Gland

The prolyl isomerase cyclophilin A (CypA) regulates the Jak2/Stat5 pathway, which is necessary for mammary differentiation and the pathogenesis of breast cancer. In this study, we assessed the role of this isomerase during mammary gland development and erbB2-driven tumorigenesis. Genetic deletion of CypA resulted in delayed mammary gland morphogenesis and differentiation with corresponding decrease in Jak2/Stat5 activation; mammary gland cross-transplantation confirmed this defect was epithelial in nature. Analysis of mammary stem and progenitor populations revealed significant disruption of epithelial maturation. Loss of CypA in the erbB2 transgenic mouse model revealed a marked increase in mammary tumor latency that correlated with decreased Stat5 activation, associated gene expression, and reduced epithelial cell proliferation. These results demonstrate an important role for CypA in the regulation of Jak2/Stat5-mediated biology in mammary epithelium, identifying this isomerase as a novel target for therapeutic intervention.Significance: These findings reveal cyclophilin A functions in normal mammary epithelial development and ErbB2-driven mammary tumorigenesis and suggest therapies targeting cyclophilin A may be efficacious for breast cancer treatment.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/14/3877/F1.large.jpg Cancer Res; 78(14); 3877-87. ©2018 AACR.

Host genetics contributes to the effectiveness of dendritic cell-based HIV immunotherapy

Systems biological analysis has recently revealed how innate immune variants as well as gut microbiota impact the individual response to immunization. HIV-infected (HIV+) patients have a worse response rate after standard vaccinations, possibly due to the immune exhaustion, increased gut permeability and microbial translocation. In the last decade, dendritic cells (DC)-based immunotherapy has been proposed as an alternative approach to control HIV plasma viral load, however clinical trials showed a heterogeneity of immunization response. Hypothesizing that host genetics may importantly affects the outcome of immunotherapy in HIV+ patients, genetic polymorphisms' distribution and gene expression modulation were analyzed in a phase I/II clinical trial of DC-based immunotherapy according to immunization response, and quality of vaccine product (DC). Polymorphisms in genes previously associated with progression of HIV infection to AIDS (i.e.: PARD3B, CCL5) contribute to a better response to immunotherapy in HIV+ individuals, possibly through a systemic effect on host immune system, but also directly on vaccine product. Genes expression profile after immunization correlates with different degrees of immune chronic activation/exhaustion of HIV+ patients (i.e. PD1, IL7RA, EOMES), but also with anti-viral response and DC quality (i.e.: APOBEC3G, IL8, PPIA), suggested that an immunocompetent individual would have a better vaccine response. These findings showed once more that host genetics can affect the response to DC-based immunotherapy in HIV+ individuals, contributing to the heterogeneity of response observed in concluded trials; and it can be used as predictor of immunization success.