Claudin-18: unexpected regulator of lung alveolar epithelial cell proliferation

Comprehensive landscape of junctional genes and their association with overall survival of patients with lung adenocarcinoma

Objectives

Junctional proteins are involved in tumorigenesis. Therefore, this study aimed to investigate the association between junctional genes and the prognosis of patients with lung adenocarcinoma (LUAD).

Methods

Transcriptome, mutation, and clinical data were retrieved from The Cancer Genome Atlas (TCGA). "Limma" was used to screen differentially expressed genes. Moreover, Kaplan-Meier survival analysis was used to identify junctional genes associated with LUAD prognosis. The junctional gene-related risk score (JGRS) was generated based on multivariate Cox regression analysis. An overall survival (OS) prediction model combining the JGRS and clinicopathological properties was proposed using a nomogram and further validated in the Gene Expression Omnibus (GEO) LUAD cohort.

Results

To our knowledge, this study is the first to demonstrate the correlation between the mRNA levels of 14 junctional genes (CDH15, CDH17, CDH24, CLDN6, CLDN12, CLDN18, CTNND2, DSG2, ITGA2, ITGA8, ITGA11, ITGAL, ITGB4, and PKP3) and clinical outcomes of patients with LUAD. The JGRS was generated based on these 14 genes, and a higher JGRS was associated with older age, higher stage levels, and lower immune scores. Thus, a prognostic prediction nomogram was proposed based on the JGRS. Internal and external validation showed the good performance of the prediction model. Mechanistically, JGRS was associated with cell proliferation and immune regulatory pathways. Mutational analysis revealed that more somatic mutations occurred in the high-JGRS group than in the low-JGRS group.

Conclusion

The association between junctional genes and OS in patients with LUAD demonstrated by our "TCGA filtrating and GEO validating" model revealed a new function of junctional genes.

Construction of a Human Immune Library from Gallbladder Cancer Patients for the Single-Chain Fragment Variable (scFv) Antibody Selection against Claudin 18.2 via Phage Display

Gallbladder cancer (GBC) is a very aggressive malignant neoplasm of the biliary tract with a poor prognosis. There are no specific therapies for the treatment of GBC or early diagnosis tools; for this reason, the development of strategies and technologies that facilitate or allow an early diagnosis of GBC continues to be decisive. Phage display is a robust technique used for the production of monoclonal antibodies (mAbs) involving (1) the generation of gene libraries, (2) the screening and selection of isoforms related to an immobilized antigen, and (3) the in vitro maturation of the affinity of the antibody for the antigen. This research aimed to construct a human immune library from PBMCs of GBC patients and the isolation of scFv-phage clones with specificity against the larger extracellular loop belonging to claudin 18.2, which is an important biomarker overexpressed in GBC as well as gastric cancer. The immune-library-denominated GALLBLA1 was constructed from seven GBC patients and has a diversity of 6.12 × 1010pfu mL-1. After three rounds of panning, we were able to identify clones with specificity against claudin 18.2. GALLBLA1 can contribute to the selection, isolation, and recombinant production of new human mAbs candidates for the treatment of gastrointestinal cancers.

Dark horse target Claudin18.2 opens new battlefield for pancreatic cancer

Pancreatic cancer is one of the deadliest malignant tumors, which is a serious threat to human health and life, and it is expected that pancreatic cancer may be the second leading cause of cancer death in developed countries by 2030. Claudin18.2 is a tight junction protein expressed in normal gastric mucosal tissues, which is involved in the formation of tight junctions between cells and affects the permeability of paracellular cells. Claudin18.2 is highly expressed in pancreatic cancer and is associated with the initiation, progression, metastasis and prognosis of cancer, so it is considered a potential therapeutic target. Up to now, a number of clinical trials for Claudin18.2 are underway, including solid tumors such as pancreatic cancers and gastric cancers, and the results of these trials have not yet been officially announced. This manuscript briefly describes the Claudia protein, the dual roles of Cluadin18 in cancers, and summarizes the ongoing clinical trials targeting Claudin18.2 with a view to integrating the research progress of Claudin18.2 targeted therapy. In addition, this manuscript introduces the clinical research progress of Claudin18.2 positive pancreatic cancer, including monoclonal antibodies, bispecific antibodies, antibody-drug conjugates, CAR-T cell therapy, and hope to provide feasible ideas for the clinical treatment of Claudin18.2 positive pancreatic cancer.

Therapeutic Targets of Monoclonal Antibodies Used in the Treatment of Cancer: Current and Emerging

Cancer is one of the leading global causes of death and disease, and treatment options are constantly evolving. In this sense, the use of monoclonal antibodies (mAbs) in immunotherapy has been considered a fundamental aspect of modern cancer therapy. In order to avoid collateral damage, it is indispensable to identify specific molecular targets or biomarkers of therapy and/or diagnosis (theragnostic) when designing an appropriate immunotherapeutic regimen for any type of cancer. Furthermore, it is important to understand the currently employed mAbs in immunotherapy and their mechanisms of action in combating cancer. To achieve this, a comprehensive understanding of the biology of cancer cell antigens, domains, and functions is necessary, including both those presently utilized and those emerging as potential targets for the design of new mAbs in cancer treatment. This review aims to provide a description of the therapeutic targets utilized in cancer immunotherapy over the past 5 years, as well as emerging targets that hold promise as potential therapeutic options in the application of mAbs for immunotherapy. Additionally, the review explores the mechanisms of actin of the currently employed mAbs in immunotherapy.

Targeting CLDN18.2 in cancers of the gastrointestinal tract: New drugs and new indications

Cancers of the gastrointestinal (GI) tract greatly contribute to the global cancer burden and cancer-related death. Claudin-18.2(CLDN18.2), a transmembrane protein, is a major component of tight junctions and plays an important role in the maintenance of barrier function. Its characteristic widespread expression in tumour tissues and its exposed extracellular loops make it an ideal target for researchers to develop targeted strategies and immunotherapies for cancers of the GI tract. In the present review, we focus on the expression pattern of CLDN18.2 and its clinical significance in GI cancer. We also discuss the tumour-promoting and/or tumour-inhibiting functions of CLDN18.2, the mechanisms regulating its expression, and the current progress regarding the development of drugs targeting CLDN18.2 in clinical research.

The role and mechanism of claudins in cancer

Claudins are a tetraspan membrane protein multigene family that plays a structural and functional role in constructing tight junctions. Claudins perform crucial roles in maintaining cell polarity in epithelial and endothelial cell sheets and controlling paracellular permeability. In the last two decades, increasing evidence indicates that claudin proteins play a major role in controlling paracellular permeability and signaling inside cells. Several types of claudins are dysregulated in various cancers. Depending on where the tumor originated, claudin overexpression or underexpression has been shown to regulate cell proliferation, cell growth, metabolism, metastasis and cell stemness. Epithelial-to-mesenchymal transition is one of the most important functions of claudin proteins in disease progression. However, the exact molecular mechanisms and signaling pathways that explain why claudin proteins are so important to tumorigenesis and progression have not been determined. In addition, claudins are currently being investigated as possible diagnostic and treatment targets. Here, we discuss how claudin-related signaling pathways affect tumorigenesis, tumor progression, and treatment sensitivity.

Niche-Dependent Regulation of Lkb1 in the Proliferation of Lung Epithelial Progenitor Cells

Lung homeostasis and regeneration depend on lung epithelial progenitor cells. Lkb1 (Liver Kinase B1) has known roles in the differentiation of airway epithelial cells during embryonic development. However, the effects of Lkb1 in adult lung epithelial progenitor cell regeneration and its mechanisms of action have not been determined. In this study, we investigated the mechanism by which Lkb1 regulates lung epithelial progenitor cell regeneration. Organoid culture showed that loss of Lkb1 significantly reduced the proliferation of club cells and alveolar type 2 (AT2) cells in vitro. In the absence of Lkb1, there is a slower recovery rate of the damaged airway epithelium in naphthalene-induced airway epithelial injury and impaired expression of surfactant protein C during bleomycin-induced alveolar epithelial damage. Moreover, the expression of autophagy-related genes was reduced in club cells and increased in AT2 cells, but the expression of Claudin-18 was obviously reduced in AT2 cells after Lkb1 knockdown. On the whole, our findings indicated that Lkb1 may promote the proliferation of lung epithelial progenitor cells via a niche-dependent pathway and is required for the repair of the damaged lung epithelium.

Asymptomatic SARS-CoV-2 Infection Is Associated With Higher Levels of Serum IL-17C, Matrix Metalloproteinase 10 and Fibroblast Growth Factors Than Mild Symptomatic COVID-19

Young adults infected with SARS-CoV-2 are frequently asymptomatic or develop only mild disease. Because capturing representative mild and asymptomatic cases require active surveillance, they are less characterized than moderate or severe cases of COVID-19. However, a better understanding of SARS-CoV-2 asymptomatic infections might shed light into the immune mechanisms associated with the control of symptoms and protection. To this aim, we have determined the temporal dynamics of the humoral immune response, as well as the serum inflammatory profile, of mild and asymptomatic SARS-CoV-2 infections in a cohort of 172 initially seronegative prospectively studied United States Marine recruits, 149 of whom were subsequently found to be SARS-CoV-2 infected. The participants had blood samples taken, symptoms surveyed and PCR tests for SARS-CoV-2 performed periodically for up to 105 days. We found similar dynamics in the profiles of viral load and in the generation of specific antibody responses in asymptomatic and mild symptomatic participants. A proteomic analysis using an inflammatory panel including 92 analytes revealed a pattern of three temporal waves of inflammatory and immunoregulatory mediators, and a return to baseline for most of the inflammatory markers by 35 days post-infection. We found that 23 analytes were significantly higher in those participants that reported symptoms at the time of the first positive SARS-CoV-2 PCR compared with asymptomatic participants, including mostly chemokines and cytokines associated with inflammatory response or immune activation (i.e., TNF-α, TNF-β, CXCL10, IL-8). Notably, we detected 7 analytes (IL-17C, MMP-10, FGF-19, FGF-21, FGF-23, CXCL5 and CCL23) that were higher in asymptomatic participants than in participants with symptoms; these are known to be involved in tissue repair and may be related to the control of symptoms. Overall, we found a serum proteomic signature that differentiates asymptomatic and mild symptomatic infections in young adults, including potential targets for developing new therapies and prognostic tests.

[A review on the effect of Claudin-18 on bronchopulmonary dysplasia in preterm infants]

Bronchopulmonary dysplasia (BPD) has the main manifestations of pulmonary edema in the early stage and characteristic alveolar obstruction and microvascular dysplasia in the late stage, which may be caused by structural and functional destruction of the lung epithelial barrier. The Claudin family is the main component of tight junction and plays an important role in regulating the permeability of paracellular ions and solutes. Claudin-18 is the only known tight junction protein solely expressed in the lung. The lack of Claudin-18 can lead to barrier dysfunction and impaired alveolar development, and the knockout of Claudin-18 can cause characteristic histopathological changes of BPD. This article elaborates on the important role of Claudin-18 in the development and progression of BPD from the aspects of lung epithelial permeability, alveolar development, and progenitor cell homeostasis, so as to provide new ideas for the pathogenesis and clinical treatment of BPD.

Tight junctions and their regulation by non-coding RNAs

Tight junction (TJ) is a “zippering up” junction structure located at the uppermost portion of adjacent epithelial/endothelial cells in organs and tissues. TJs maintain the relative stability of intracellular substances and functions by closing or opening intercellular pathways, coordinating the entry and exit of molecules of different sizes and charges, and regulating the permeability of paracellular barrier. TJs also prevent microbial invasion, maintain epithelial/endothelial cell polarity, and regulate cell proliferation. TJs are widely present in the skin and mucosal epithelial barriers, intestinal epithelial barrier, glomerular filtration barrier, bladder epithelial barrier, blood-brain barrier, brain-blood tumor barrier, and blood-testis barrier. TJ dysfunction in different organs can lead to a variety of diseases. In addition to signal pathways, transcription factors, DNA methylation, histone modification, TJ proteins can also be regulated by a variety of non-coding RNAs, such as micro-RNAs, long-noncoding RNAs, and circular RNAs, directly or indirectly. This review summarizes the structure of TJs and introduces the functions and regulatory mechanisms of TJs in different organs and tissues. The roles and mechanisms of non-coding RNAs in the regulation of TJs are also highlighted in this review.

Pre-exposure to hydrogen sulfide modulates the innate inflammatory response to organic dust

Animal production units produce and store many contaminants on-site, including organic dust (OD) and hydrogen sulfide (H₂S). Workers in these settings report various respiratory disease symptoms. Both OD and H₂S have shown to induce lung inflammation. However, impact of co-exposure to both H₂S and OD has not been investigated. Therefore, we tested a hypothesis that pre-exposure to H₂S modulates the innate inflammatory response of the lungs to organic dust. In a mouse model of H₂S and organic dust extract (ODE) exposure, we assessed lung inflammation quantitatively. We exposed human airway epithelial and monocytic cells to medium or H₂S alone or H₂S followed by ODE and measured cell viability, oxidative stress, and other markers of inflammation. Exposure to 10 ppm H₂S followed by ODE increased the lavage fluid leukocytes. However, exposure to 10 ppm H₂S alone resulted in changes in tight junction proteins, an increase in mRNA levels of tlr2 and tlr4 as well as ncf1, ncf4, hif1α, and nrf2. H₂S alone or H₂S and ODE exposure decreased cell viability and increased reactive nitrogen species production. ODE exposure increased the transcripts of tlr2 and tlr4 in both in vitro and in vivo models, whereas increased nfkbp65 transcripts following exposure to ODE and H₂S was seen only in in vitro model. H₂S alone and H₂S followed by ODE exposure increased the levels of IL-1β. We conclude that pre-exposure to H₂S modulates lung innate inflammatory response to ODE.

Ruffles and spikes: Control of tight junction morphology and permeability by claudins

Epithelial barrier function is regulated by a family of transmembrane proteins known as claudins. Functional tight junctions are formed when claudins interact with other transmembrane proteins, cytosolic scaffold proteins and the actin cytoskeleton. The predominant scaffold protein, zonula occludens-1 (ZO-1), directly binds to most claudin C-terminal domains, crosslinking them to the actin cytoskeleton. When imaged by immunofluorescence microscopy, tight junctions most frequently are linear structures that form between tricellular junctions. However, tight junctions also adapt non-linear architectures exhibiting either a ruffled or spiked morphology, which both are responses to changes in claudin engagement of actin filaments. Other terms for ruffled tight junctions include wavy, tortuous, undulating, serpentine or zig-zag junctions. Ruffling is under the control of hypoxia induced factor (HIF) and integrin-mediated signaling, as well as direct mechanical stimulation. Tight junction ruffling is specifically enhanced by claudin-2, antagonized by claudin-1 and requires claudin binding to ZO-1. Tight junction spikes are sites of active vesicle budding and fusion that appear as perpendicular projections oriented towards the nucleus. Spikes share molecular features with focal adherens junctions and tubulobulbar complexes found in Sertoli cells. Lung epithelial cells under stress form spikes due to an increase in claudin-5 expression that directly disrupts claudin-18/ZO-1 interactions. Together this suggests that claudins are not simply passive cargoes controlled by scaffold proteins. We propose a model where claudins specifically influence tight junction scaffold proteins to control interactions with the cytoskeleton as a mechanism that regulates tight junction assembly and function.

CLDN6 promotes tumor progression through the YAP1-snail1 axis in gastric cancer

Claudin6 (CLDN6), a member of the tight junction family, is a molecule involved in intercellular adhesion, acting as a physical barrier that prevents solutes and water from freely passing through the extracellular space. CLDN6 has important biological functions, and its abnormal expression is associated with Hepatitis C infection. However, there is limited research regarding its role in gastric cancer. In this study, we found that the expression of CLDN6 mRNA and protein was upregulated in gastric cancer cell lines and tissues, which indicated poor prognosis. Both in vitro and in vivo experiments showed that abnormal CLDN6 expression was associated with enhanced proliferation and invasion abilities of gastric cancer. CLDN6 reduced the phosphorylation of LATS1/2 and YAP1 by interacting with LATS1/2 in the Hippo signaling pathway. Thus, CLDN6 affected the entry of YAP1 into the nucleus, causing changes in downstream target genes. Moreover, YAP1 interacted with snail1 to affect the process of EMT and enhanced the invasive ability of GC cells. Collectively, CLDN6 promoted the proliferation and invasive ability of gastric cancer by affecting YAP1 and YAP1-snail1 axis.

Choroid plexus genes for CSF production and brain homeostasis are altered in Alzheimer's disease

Background

The roles of the choroid plexus (CP) and cerebrospinal fluid (CSF) production have drawn increasing attention in Alzheimer’s disease (AD) research. Specifically, studies document markedly decreased CSF production and turnover in moderate-to-severe AD. Moreover, reduced CP function and CSF turnover lead to impaired clearance of toxic metabolites, likely promote neuroinflammation, and may facilitate neuronal death during AD progression. We analyzed CP gene expression in AD compared with control subjects, specifically considering those genes involved with CSF production and CP structural integrity.

Methods

The Brown-Merck Gene Expression Omnibus (GEO) database (CP transcripts) was mined to examine changes in gene expression in AD compared to controls with a focus on assorted genes thought to play a role in CSF production. Specifically, genes coding for ion transporters in CP epithelium (CPE) and associated enzymes like Na–K-ATPase and carbonic anhydrase, aquaporins, mitochondrial transporters/enzymes, blood–cerebrospinal fluid barrier (BCSFB) stability proteins, and pro-inflammatory mediators were selected for investigation. Data were analyzed using t test p-value and fold-change analysis conducted by the GEO2R feature of the GEO database.

Results

Significant expression changes for several genes were observed in AD CP. These included disruptions to ion transporters (e.g., the solute carrier gene SLC4A5, p = 0.004) and associated enzyme expressions (e.g., carbonic anhydrase CA4, p = 0.0001), along with decreased expression of genes involved in BCSFB integrity (e.g., claudin CLDN5, p = 0.039) and mitochondrial ATP synthesis (e.g., adenosine triphosphate ATP5L, p = 0.0004). Together all changes point to disrupted solute transport at the blood–CSF interface in AD. Increased expression of pro-inflammatory (e.g., interleukin IL1RL1, p = 0.00001) and potential neurodegenerative genes (e.g., amyloid precursor APBA3, p = 0.002) also implicate disturbed CP function.

Conclusions

Because the altered expression of numerous transcripts in AD-CP help explain decreased CSF production in AD, these findings represent a first step towards identifying novel therapeutic targets in AD.

Electronic supplementary material

The online version of this article (10.1186/s12987-018-0120-7) contains supplementary material, which is available to authorized users.