The Expression of the Claudin Family of Proteins in Colorectal Cancer.

Claudins (CLDN1-CLDN24) are a family of tight junction proteins whose dysregulation has been implicated in tumorigeneses of many cancer types. In colorectal cancer (CRC), CLDN1, CLDN2, CLDN4, and CLDN18 have been shown to either be upregulated or aberrantly expressed. In the normal colon, CLDN1 and CLDN3-7 are expressed. Although a few claudins, such as CLDN6 and CLDN7, are expressed in CRC their levels are reduced compared to the normal colon. The present review outlines the expression profiles of claudin proteins in CRC and those that are potential biomarkers for prognostication.

Loss of Claudin-1 incurred by DNMT aberration promotes pancreatic cancer progression.

Pancreatic cancer (PC) is one of the most malignant and deadly tumors of digestive system with complex etiology and pathogenesis. Dysregulations of oncogenes and tumor suppressors due to epigenetic modifications causally affect tumorogenesis; however the key tumor suppressors and their regulations in PC are only partially defined. In this study, we found that Claudin-1 (encoded by CLDN1 gene) was significantly suppressed in PC that correlated with a poor clinical prognosis. Claudin-1 knockdown enhanced PC cell proliferation, migration, and stemness. Pancreatic specific Cldn1 knockout in KPC (LSLKrasG12D/Pdx1-Cre/Trp53R172H+) and KC (LSLKrasG12D/Pdx1-Cre) mice reduced mouse survival, promoted acinar-to-ductal metaplasia (ADM) process, and accelerated the development of pancreatic intraepithelial neoplasia (PanIN) and PC. Further investigation revealed that Claudin-1 suppression was mainly caused by aberrant DNA methylatransferase 1 (DNMT1) and DNMT3A elevations and the resultant CLDN1 promoter hypermethylation, as a DNMT specific inhibitor SGI-1027 effectively reversed the Claudin-1 suppression and inhibited PC progression both in vitro and in vivo in a Claudin-1 preservation-dependent manner. Together, our data suggest that Claudin-1 functions as a tumor suppressor in PC and its epigenetic suppression due to DNMT aberrations is a crucial event that promotes PC development and progression.

Ameliorative Effects of Zingiber officinale Rosc on Antibiotic-Associated Diarrhea and Improvement in Intestinal Function.

The global increase in antibiotic consumption is related to increased adverse effects, such as antibiotic-associated diarrhea (AAD). This study investigated the chemical properties of Zingiber officinale Rosc (ZO) extract and its ameliorative effects using a lincomycin-induced AAD mouse model. Intestinal tissues were evaluated for the expression of lysozyme, claudin-1, and α-defensin-1, which are associated with intestinal homeostasis. The cecum was analyzed to assess the concentration of short-chain fatty acids (SCFAs). The chemical properties analysis of ZO extracts revealed the levels of total neutral sugars, acidic sugars, proteins, and polyphenols to be 86.4%, 8.8%, 4.0%, and 0.8%, respectively. Furthermore, the monosaccharide composition of ZO was determined to include glucose (97.3%) and galactose (2.7%). ZO extract administration ameliorated the impact of AAD and associated weight loss, and water intake also returned to normal. Moreover, treatment with ZO extract restored the expression levels of lysozyme, α-defensin-1, and claudin-1 to normal levels. The decreased SCFA levels due to induced AAD showed a return to normal levels. The results indicate that ZO extract improved AAD, strengthened the intestinal barrier, and normalized SCFA levels, showing that ZO extract possesses intestinal-function strengthening effects.

TMEM25 is a Par3-binding protein that attenuates claudin assembly during tight junction development.

The tight junction (TJ) in epithelial cells is formed by integral membrane proteins and cytoplasmic scaffolding proteins. The former contains the claudin family proteins with four transmembrane segments, while the latter includes Par3, a PDZ domain-containing adaptor that organizes TJ formation. Here we show the single membrane-spanning protein TMEM25 localizes to TJs in epithelial cells and binds to Par3 via a PDZ-mediated interaction with its C-terminal cytoplasmic tail. TJ development during epithelial cell polarization is accelerated by depletion of TMEM25, and delayed by overexpression of TMEM25 but not by that of a C-terminally deleted protein, indicating a regulatory role of TMEM25. TMEM25 associates via its N-terminal extracellular domain with claudin-1 and claudin-2 to suppress their cis- and trans-oligomerizations, both of which participate in TJ strand formation. Furthermore, Par3 attenuates TMEM25-claudin association via binding to TMEM25, implying its ability to affect claudin oligomerization. Thus, the TJ protein TMEM25 appears to negatively regulate claudin assembly in TJ formation, which regulation is modulated by its interaction with Par3.

Activation of the TGF-ß1/EMT signaling pathway by claudin-1 overexpression reduces doxorubicin sensitivity in small cell lung cancer SBC-3 cells.

Small-cell lung cancer (SCLC), which accounts for about 15 % of all lung cancers, progresses more rapidly than other histologic types and is rarely detected at an operable early stage. Therefore, chemotherapy, radiation therapy, or their combination are the primary treatments for this type of lung cancer. However, the tendency to acquire resistance to anticancer drugs is a severe problem. Recently, we found that an intercellular adhesion molecule, claudin (CLDN) 1, known to be involved in the migration and invasion of lung cancer cells, is involved in the acquisition of anticancer drug resistance. In the present study, we investigated the effect of CLDN1 on the anticancer-drug sensitivity of SCLC SBC-3 cells. Since epithelial-mesenchymal transition (EMT), which is involved in cancer cell migration and invasion, is well known for its involvement in anticancer-drug sensitivity via inhibition of apoptosis, we also examined EMT involvement in decreased anticancer-drug sensitivity by CLDN1. Sensitivity to doxorubicin (DOX) in SBC-3 cells was significantly decreased by CLDN1 overexpression. CLDN1 overexpression resulted in increased TGF-ß1 levels, enhanced EMT induction, and increased migratory potency of SBC-3 cells. The decreased sensitivity of SBC-3 cells to anticancer drugs upon TGF-ß1 treatment suggested that activation of the TGF-ß1/EMT signaling pathway by CLDN1 causes the decreased sensitivity to anticancer drugs and increased migratory potency. Furthermore, treatments with antiallergic agents tranilast and zoledronic acid, known EMT inhibitors, significantly mitigated the decreased sensitivity of CLDN1-overexpressing SBC-3 cells to DOX. These results suggest that EMT inhibitors might effectively overcome reduced sensitivity to anticancer drugs in CLDN1-overexpressing SCLC cells.

CLDN1 Arg81His founder variant causes ichthyosis, leukocyte vacuoles, alopecia, and sclerosing cholangitis (ILVASC) syndrome in Moroccan Jews.

Neonatal ichthyosis and sclerosing cholangitis syndrome (NISCH), also known as ichthyosis, leukocyte vacuoles, alopecia, and sclerosing cholangitis (ILVASC), is an extremely rare disease of autosomal recessive inheritance, resulting from loss of function of the tight junction protein claudin-1. Its clinical presentation is highly variable, and is characterized by liver and ectodermal involvement. Although most ILVASC cases described to date were attributed to homozygous truncating variants in CLDN1, a single missense variant CLDN1 p.Arg81His, associated with isolated skin ichthyosis phenotype, has been recently reported in a family of Moroccan Jewish descent. We now describe seven patients with ILVASC, originating from four non consanguineous families of North African Jewish ancestry (including one previously reported family), harboring CLDN1 p.Arg81His variant, and broaden the phenotypic spectrum attributed to this variant to include teeth, hair, and liver/bile duct involvement, characteristic of ILVASC. Furthermore, we provide additional evidence for pathogenicity of the CLDN1 p.Arg81His variant by transmission electron microscopy of the affected skin, revealing distorted tight junction architecture, and show through haplotype analysis in the vicinity of the CLDN1 gene, that this variant represents a founder variant in Jews of Moroccan descent with an estimated carrier frequency of 1:220.

Torreya grandis Kernel Oil Alleviates Loperamide-Induced Slow Transit Constipation via Up-Regulating the Colonic Expressions of Occludin/Claudin-1/ZO-1 and 5-HT3R/5-HT4R in BALB/c Mice.

SCOPE: Torreya grandis kernel has traditionally been used to remove intestinal parasites and increases intestinal motility. However, the effect of Torreya grandis kernel oil (TKO) on constipation has not yet been investigated. Therefore, mouse model is used to investigate the effect of TKO on slow transit constipation (STC) and its possible mechanism. METHODS AND RESULTS: The effects of TKO on intestinal motility of STC mice are evaluated by fecal weight, fecal water content, colon length, defecation test, and intestinal propulsion test. The mechanism of TKO alleviating STC is explored by detecting biochemical analysis, histological analysis, western blot, qRT-PCR, immunohistochemistry, and gut microbiota analysis. The results reveal that TKO effectively promotes defecation and intestinal motility, increases the level of endothelin-1, and restores the histopathological morphology of the colon under LOP pretreatment. The expression levels of occludin, claudin-1, and zonula occludens-1 (ZO-1) mRNA and protein are up-regulated in mice receiving TKO treatment. The colonic 5-hydroxytryptamine 3R/4R (5-HT3R/5-HT4R) expressions are also increased by TKO supplementation. Additionally, TKO rescues LOP-caused disorders of the gut microbiota. CONCLUSION: Consumption of TKO is beneficial to STC recovery, and it can alleviate LOP-induced STC by up-regulating the colonic expressions of Occludin/Claudin-1/ZO-1 and 5-HT3R/5-HT4R.

Acrolein suppresses anticancer drug-induced toxicity mediated by activating claudin-1 and Nrf2 axis in a spheroid model of human lung squamous cell carcinoma cells.

Tobacco smoke contains various carcinogenic ingredients such as nicotine, acrolein, and benzopyrene; however, their effects on cancer treatment are not fully understood. Claudin-1 (CLDN1), a component of tight junctions, is involved in the increased resistance to anticancer drugs. In this study, we found that acrolein increases the mRNA and protein levels of CLDN1 in RERF-LC-AI cells derived from human lung squamous cell carcinoma (SCC). Acrolein increased the p-extracellular signal-regulated kinase (ERK) 1/2 levels without affecting the p-Akt level. The acrolein-induced elevation of CLDN1 expression was attenuated by U0126, a mitogen-activated protein kinase kinas (MEK) inhibitor. These results indicate that the activation of MEK/ERK pathway is involved in the acrolein-induced elevation of CLDN1 expression. In a spheroid model, acrolein suppressed the accumulation and toxicity of doxorubicin (DXR), which were rescued by CLDN1 silencing. The acrolein-induced effects were also observed in lung SCC-derived EBC-1 and LK-2 cells. Acrolein also increased the expression level of nuclear factor erythroid 2-related factor 2 (Nrf2), a transcription factor that regulates antioxidant and detoxifying genes, which were inhibited by CLDN1 silencing. In spheroid cells, the levels of reactive oxygen species were enhanced by acrolein, which was inhibited by CLDN1 silencing. Taken together, acrolein may reduce the anticancer drug-induced toxicity in human lung SCC cells mediated by high CLDN1 expression followed by the upregulation of Nrf2 signaling pathway.

Trichinella spiralis cathepsin L damages the tight junctions of intestinal epithelial cells and mediates larval invasion.

BACKGROUND: Cathepsin L, a lysosomal enzyme, participates in diverse physiological processes. Recombinant Trichinella spiralis cathepsin L domains (rTsCatL2) exhibited natural cysteine protease activity and hydrolyzed host immunoglobulin and extracellular matrix proteins in vitro, but its functions in larval invasion are unknown. The aim of this study was to explore its functions in T. spiralis invasion of the host's intestinal epithelial cells. METHODOLOGY/PRINCIPAL FINDINGS: RNAi significantly suppressed the expression of TsCatL mRNA and protein with TsCatL specific siRNA-302. T. spiralis larval invasion of Caco-2 cells was reduced by 39.87% and 38.36%, respectively, when anti-TsCatL2 serum and siRNA-302 were used. Mice challenged with siRNA-302-treated muscle larvae (ML) exhibited a substantial reduction in intestinal infective larvae, adult worm, and ML burden compared to the PBS group, with reductions of 44.37%, 47.57%, and 57.06%, respectively. The development and fecundity of the females from the mice infected with siRNA-302-treated ML was significantly inhibited. After incubation of rTsCatL2 with Caco-2 cells, immunofluorescence test showed that the rTsCatL2 gradually entered into the cells, altered the localization of cellular tight junction proteins (claudin 1, occludin and zo-1), adhesion junction protein (e-cadherin) and extracellular matrix protein (laminin), and intercellular junctions were lost. Western blot showed a 58.65% reduction in claudin 1 expression in Caco-2 cells treated with rTsCatL2. Co-IP showed that rTsCatL2 interacted with laminin and collagen I but not with claudin 1, e-cadherin, occludin and fibronectin in Caco-2 cells. Moreover, rTsCatL2 disrupted the intestinal epithelial barrier by inducing cellular autophagy. CONCLUSIONS: rTsCatL2 disrupts the intestinal epithelial barrier and facilitates T. spiralis larval invasion.

Evaluation of glomerular sirtuin-1 and claudin-1 in the pathophysiology of nondiabetic focal segmental glomerulosclerosis.

Focal segmental glomerulosclerosis (FSGS) is the leading cause of nephrotic syndrome, which is characterized by podocyte injury. Given that the pathophysiology of nondiabetic glomerulosclerosis is poorly understood and targeted therapies to prevent glomerular disease are lacking, we decided to investigate the tight junction protein claudin-1 and the histone deacetylase sirtuin-1 (SIRT1), which are known to be involved in podocyte injury. For this purpose, we first examined SIRT1, claudin-1 and podocin expression in kidney biopsies from patients diagnosed with nondiabetic FSGS and found that upregulation of glomerular claudin-1 accompanies a significant reduction in glomerular SIRT1 and podocin levels. From this, we investigated whether a small molecule activator of SIRT1, SRT1720, could delay the onset of FSGS in an animal model of adriamycin (ADR)-induced nephropathy; 14 days of treatment with SRT1720 attenuated glomerulosclerosis progression and albuminuria, prevented transcription factor Wilms tumor 1 (WT1) downregulation and increased glomerular claudin-1 in the ADR + SRT1720 group. Thus, we evaluated the effect of ADR and/or SRT1720 in cultured mouse podocytes. The results showed that ADR [1 µM] triggered an increase in claudin-1 expression after 30 min, and this effect was attenuated by pretreatment of podocytes with SRT1720 [5 µM]. ADR [1 µM] also led to changes in the localization of SIRT1 and claudin-1 in these cells, which could be associated with podocyte injury. Although the use of specific agonists such as SRT1720 presents some benefits in glomerular function, their underlying mechanisms still need to be further explored for therapeutic use. Taken together, our data indicate that SIRT1 and claudin-1 are relevant for the pathophysiology of nondiabetic FSGS.

Epithelial Barrier Dysfunction in Diarrhea-Predominant Irritable Bowel Syndrome (IBS-D) via Downregulation of Claudin-1.

BACKGROUND: In patients with diarrhea-predominant irritable bowel syndrome (IBS-D), the diarrheal mechanisms are largely unknown, and they were examined in this study on colon biopsies. METHODS: Electrophysiological measurements were used for monitoring functional changes in the diarrheic colon specimens. In parallel, tight junction protein expression was analyzed by Western blot and confocal laser-scanning microscopy, and signaling pathway analysis was performed using RNA sequencing and bioinformatics. RESULTS: Epithelial resistance was decreased, indicating an epithelial leak flux diarrheal mechanism with a molecular correlate of decreased claudin-1 expression, while induction of active anion secretion and impairment of active sodium absorption via the epithelial sodium channel, ENaC, were not detected. The pathway analysis revealed activation of barrier-affecting cytokines TNF-α, IFN-γ, IL-1ß and IL-4. CONCLUSIONS: Barrier dysfunction as a result of epithelial tight junction changes plays a role in IBS-D as a pathomechanism inducing a leak flux type of diarrhea.

Roles of epidermal growth factor receptor, claudin-1 and occludin in multi-step entry of hepatitis C virus into polarized hepatoma spheroids.

The multi-step process of hepatitis C virus (HCV) entry is facilitated by various host factors, including epidermal growth factor receptor (EGFR) and the tight junction proteins claudin-1 (CLDN1) and occludin (OCLN), which are thought to function at later stages of the HCV entry process. Using single particle imaging of HCV infection of polarized hepatoma spheroids, we observed that EGFR performs multiple functions in HCV entry, both phosphorylation-dependent and -independent. We previously observed, and in this study confirmed, that EGFR is not required for HCV migration to the tight junction. EGFR is required for the recruitment of clathrin to HCV in a phosphorylation-independent manner. EGFR phosphorylation is required for virion internalization at a stage following the recruitment of clathrin. HCV entry activates the RAF-MEK-ERK signaling pathway downstream of EGFR phosphorylation. This signaling pathway regulates the sorting and maturation of internalized HCV into APPL1- and EEA1-associated early endosomes, which form the site of virion uncoating. The tight junction proteins, CLDN1 and OCLN, function at two distinct stages of HCV entry. Despite its appreciated function as a "late receptor" in HCV entry, CLDN1 is required for efficient HCV virion accumulation at the tight junction. Huh-7.5 cells lacking CLDN1 accumulate HCV virions primarily at the initial basolateral surface. OCLN is required for the late stages of virion internalization. This study produced further insight into the unusually complex HCV endocytic process.

Claudin-1 interacts with EPHA2 to promote cancer stemness and chemoresistance in colorectal cancer.

Therapy resistance is the primary problem in treating late-stage colorectal cancer (CRC). Claudins are frequently dysregulated in cancer, and several are being investigated as novel therapeutic targets and biomarkers. We have previously demonstrated that Claudin-1 (CLDN1) expression in CRC promotes epithelial-mesenchymal transition, metastasis, and resistance to anoikis. Here, we hypothesize that CLDN1 promotes cancer stemness and chemoresistance in CRC. We found that high CLDN1 expression in CRC is associated with cancer stemness and chemoresistance signaling pathways in patient datasets, and it promotes chemoresistance both in vitro and in vivo. Using functional stemness assays, proteomics, biophysical binding assays, and patient-derived organoids, we found that CLDN1 promotes properties of cancer stemness including CD44 expression, tumor-initiating potential, and chemoresistance through a direct interaction with ephrin type-A receptor 2 (EPHA2) tyrosine kinase. This interaction is dependent on the CLDN1 PDZ-binding motif, increases EPHA2 protein expression by inhibiting its degradation, and enhances downstream AKT signaling and CD44 expression to promote stemness and chemoresistance. These results suggest CLDN1 is a viable target for pharmacological intervention and/or biomarker development.

CLDN1 silencing suppresses the proliferation and migration of airway smooth muscle cells by modulating MMP14.

Airway remodeling is an important pathologic factor in the progression of asthma. Abnormal proliferation and migration of airway smooth muscle cells (ASMCs) are important pathologic mechanisms in severe asthma. In the current study, claudin-1 (CLDN1) was identified as an asthma-related gene and was upregulated in ASMCs stimulated with platelet-derived growth factor BB (PDGF-BB). Cell counting kit-8 and EdU assays were used to evaluate cell proliferation, and transwell assay was carried out to analyze cell migration and invasion. The levels of inflammatory factors were detected using enzyme-linked immunosorbent assay. The results showed that CLDN1 knockdown inhibited the proliferation, migration, invasion, and inflammation of ASMCs treated with PDGF-BB, whereas overexpression of CLDN1 exhibited the opposite effects. Protein-protein interaction assay and co-immunoprecipitation revealed that CLDN1 directly interacted with matrix metalloproteinase 14 (MMP14). CLDN1 positively regulated MMP14 expression in asthma, and MMP14 overexpression reversed cell proliferation, migration, invasion, and inflammation induced by silenced CLDN1. Taken together, CLDN1 promotes PDGF-BB-induced cell proliferation, migration, invasion, and inflammatory responses of ASMCs by upregulating MMP14 expression, suggesting a potential role for CLDN1 in airway remodeling in asthma.

Colitis induced by PD-1 inhibitor combined with platinum-containing dual drug chemotherapy in Lewis mice and its mechanism.

Aims: To explore the occurrence and possible mechanism of colitis in Lewis mice treated with PD-1 inhibitor combined with platinum-containing dual drug chemotherapy. Subjects and Methods: A Lewis lung cancer model of C57BL/6 mice was established, randomly divided into the treatment group (group C, PD-1 inhibitor + Carboplatin (CARB) + Pemetrexed (PEM)) and model group (group B, normal saline), and a control group (group A, normal saline) was set up. Observe the changes in tumor-free weight, tumor volume, disease activity index (DAI), colon histopathology, identify serum interleukin (IL)-10, interferon (IFN)-γ, the expression of claudin-1, and occludin mRNA in the colon in each animals. Results: Compared with group A, the tumor-free weight of mice in B decreased (P < 0.001), the content of IL-10 in serum increased (P < 0.01), the content of IFN-γ in serum decreased (P < 0.01). Compared with group B, the transplanted tumor volume in C was reduced (P < 0.05), DAI scores of D4 (P < 0.001), and D7 (P < 0.001) were increased, colonic histopathology analysis showed that colitis occurred, serum IL-10 content was decreased (P < 0.05), IFN-γ content was increased (P < 0.05), and the mRNA expression of claudin-1 (P < 0.05) and occludin (P < 0.05) was reduced. Conclusions: This treatment can inhibit the growth of transplanted tumors but will cause colitis in Lewis mice. The impairment of intestinal barrier function following administration cause an imbalance in the expression of pro-inflammatory and anti-inflammatory factors in the colon, thus causing colitis.

Wild blueberry (V. angustifolium) improves TNFα-induced cell barrier permeability through claudin-1 and oxidative stress modulation in Caco-2 cells.

Increasing evidence links the impairment of intestinal permeability (IP), a feature of the intestinal barrier, to numerous dysmetabolic and dysfunctional conditions. Several host and environmental factors, including dietary factors, can negatively and/or positively affect IP. In this regard, polyphenol-rich foods including berries have been proposed as potential IP modulators. However, the exact mechanisms involved are not yet fully elucidated. The aim of the present study was to evaluate the effect of a wild blueberry (WB; V. angustifolium) powder, naturally rich in polyphenols, to affect Caco-2 cell monolayer permeability and to identify the potential mechanisms in modulating the IP process. Caco-2 cells were incubated with TNF-α (10 ng mL-1), as a pro-inflammatory stimulus, and supplemented for 24 hours with different concentrations (1 and 5 mg mL-1) of WB powder. The integrity of the intestinal cell monolayer was evaluated by measuring the transepithelial electrical resistance (TEER) and the paracellular transport of FITC-dextran. In addition, the production of the tight junction proteins, such as claudin-1 and occludin, as well as protein carbonyl and 8-hydroxy 2 deoxyguanosine, as oxidative stress markers, were quantified in the supernatant by ELISA kits. Overall, the treatment with WB powder (5 mg mL-1) mitigated the loss of Caco-2 cell barrier integrity, as documented by an increase in TEER and a reduction in FITC values. This modulation was accompanied by an upregulation of claudin-1 and a reduction of 8-OHdG. Conversely, no effect was documented for the lower concentration (1 mg mL-1) and the other IP markers, as well as oxidative stress markers analysed. In conclusion, our findings suggest a potential role of WB in the modulation of cell barrier integrity. This modulation process could be attributed to an increase in claudin-1 expression and a reduction in 8-OHdG. Further studies should be performed to corroborate the results obtained. In addition, since the effects were observed at doses of WB achievable with the diet, these findings should be substantiated also through in vivo approaches.

Downregulation of CLDN1 impairs trophoblast invasion and endovascular trophoblast differentiation in early-onset preeclampsia.

INTRODUCTION: To investigate the role of claudin-1 (CLDN1) in trophoblast invasion and endovascular trophoblast (enEVT) differentiation in early-onset preeclampsia (EOPE). METHODS: The expression and localization of CLDN1 in normal (n = 18) and EOPE (n = 20) placental tissues were detected by immunohistochemical (IHC) staining, quantitative real-time polymerase chain reaction (qRT‒PCR) and Western blotting. Next, invasion, migration and tube formation assays were performed to explore the involvement of CLDN1 in trophoblast invasion and enEVT differentiation in trophoblast cell lines (HTR8/SVneo). Then, invasion and enEVT markers were analyzed via Western blotting and qRT‒PCR, respectively. Finally, we established an EOPE mouse model to detect the Cldn1 protein level. RESULTS: CLDN1 expression was significantly decreased in EOPE placental tissues. Knockdown of CLDN1 suppressed HTR8/SVneo cell invasion, migration and the ability to penetrate the endothelial tube. Conversely, overexpression of CLDN1 promoted trophoblast invasion and the ability to invade the endothelial tube. Inhibition of CLDN1 decreased the protein expression of VIM and SNAIL along with downregulating IL1B and PECAM1 mRNA levels, while overexpression of CLDN1 gave the opposite results. In the EOPE mouse model, we found a decrease in Cldn1 expression in EOPE mouse placentas. DISCUSSION: These results suggest that the downregulation of CLDN1 in trophoblast cells is involved in the pathogenesis of early-onset preeclampsia by affecting trophoblast invasion and enEVT differentiation.

LIN28B promotes cell invasion and colorectal cancer metastasis via CLDN1 and NOTCH3.

The RNA-binding protein LIN28B is overexpressed in over 30% of patients with colorectal cancer (CRC) and is associated with poor prognosis. In the present study, we unraveled a potentially novel mechanism by which LIN28B regulates colonic epithelial cell-cell junctions and CRC metastasis. Using human CRC cells (DLD-1, Caco-2, and LoVo) with either knockdown or overexpression of LIN28B, we identified claudin 1 (CLDN1) tight junction protein as a direct downstream target and effector of LIN28B. RNA immunoprecipitation revealed that LIN28B directly binds to and posttranscriptionally regulates CLDN1 mRNA. Furthermore, using in vitro assays and a potentially novel murine model of metastatic CRC, we show that LIN28B-mediated CLDN1 expression enhances collective invasion, cell migration, and metastatic liver tumor formation. Bulk RNA sequencing of the metastatic liver tumors identified NOTCH3 as a downstream effector of the LIN28B/CLDN1 axis. Additionally, genetic and pharmacologic manipulation of NOTCH3 signaling revealed that NOTCH3 was necessary for invasion and metastatic liver tumor formation. In summary, our results suggest that LIN28B promotes invasion and liver metastasis of CRC by posttranscriptionally regulating CLDN1 and activating NOTCH3 signaling. This discovery offers a promising new therapeutic option for metastatic CRC to the liver, an area where therapeutic advancements have been relatively scarce.

GB Virus B and Hepatitis C Virus, Distantly Related Hepaciviruses, Share an Entry Factor, Claudin-1.

Due to increased and broadened screening efforts, the last decade has seen a rapid expansion in the number of viral species classified into the Hepacivirus genus. Conserved genetic features of hepaciviruses suggest that they have undergone specific adaptation and have evolved to hijack similar host proteins for efficient propagation in the liver. Here, we developed pseudotyped viruses to elucidate the entry factors of GB virus B (GBV-B), the first hepacivirus described in an animal after hepatitis C virus (HCV). GBV-B-pseudotyped viral particles (GBVBpp) were shown to be uniquely sensitive to the sera of tamarins infected with GBV-B, validating their usefulness as a surrogate for GBV-B entry studies. We screened GBVBpp infection of human hepatoma cell lines that were CRISPR/Cas9 engineered to ablate the expression of individual HCV receptors/entry factors and found that claudin-1 is essential for GBV-B infection, indicating the GBV-B and HCV share an entry factor. Our data suggest that claudin-1 facilitates HCV and GBV-B entry through distinct mechanisms since the former requires the first extracellular loop and the latter is reliant on a C-terminal region containing the second extracellular loop. The observation that claudin-1 is an entry factor shared between these two hepaciviruses suggests that the tight junction protein is of fundamental mechanistic importance during cell entry. IMPORTANCE Hepatitis C virus (HCV) is a major public health burden; approximately 58 million individuals have chronic HCV infection and are at risk of developing cirrhosis and liver cancer. To achieve the World Health Organization's target of eliminating hepatitis by 2030, new therapeutics and vaccines are needed. Understanding how HCV enters cells can inform the design of new vaccines and treatments targeting the first stage of infection. However, the HCV cell entry mechanism is complex and has been sparsely described. Studying the entry of related hepaciviruses will increase the knowledge of the molecular mechanisms of the first stages of HCV infection, such as membrane fusion, and inform structure-guided HCV vaccine design; in this work, we have identified a protein, claudin-1, that facilitates the entry of an HCV-related hepacivirus but with a mechanism not described for HCV. Similar work on other hepaciviruses may unveil a commonality of entry factors and, possibly, new mechanisms.

Ling Zhi-8, a fungal immunomodulatory protein in Ganoderma lucidum, alleviates CPT-11-induced intestinal injury via restoring claudin-1 expression.

CPT-11 (Irinotecan) remains an important chemotherapeutic agent against various solid tumors nowadays. Potential adverse effects, especially gastrointestinal toxicities, are the main limiting factor for its clinical utility. Ling Zhi-8 (LZ-8), a fungal immunomodulatory protein in Ganoderma lucidum mycelia, has potential for drug development due to its multiple bioactivities and functions. This study aimed to explore the influence of LZ-8 on CPT-11-treated IEC-6 cells in vitro and on mice with CPT-11-induced intestinal injury in vivo. The mechanism through which LZ-8 exerted its protective effects was also investigated. In the in vitro study, the viability and claudin-1 expression of IEC-6 cells decreased gradually with increasing concentrations of CPT-11, but LZ-8 treatment had no obvious influence on their viability, morphology, and claudin-1 expression. Pretreatment of LZ-8 significantly improved CPT-11-decreased cell viability and claudin-1 expression in IEC-6 cells. In mice with CPT-11-induced intestinal injury, LZ-8 treatment could ameliorate symptoms and mitigate intestinal damage. Meanwhile, LZ-8 restored claudin-1 expression in the intestinal membranes in CPT-11-treated mice. Collectively, our results demonstrated the protective effects of LZ-8 against CPT-11 damage in both IEC-6 cells and mice. LZ-8 can restore claudin-1 expression in intestinal cells following CPT-11 treatment, suggesting the role of claudin-1 in the scenario.