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.

SPAK-p38 MAPK signal pathway modulates claudin-18 and barrier function of alveolar epithelium after hyperoxic exposure

BACKGROUND

Hyperoxia downregulates the tight junction (TJ) proteins of the alveolar epithelium and leads to barrier dysfunction. Previous study has showed that STE20/SPS1-related proline/alanine-rich kinase (SPAK) interferes with the intestinal barrier function in mice. The aim of the present study is to explore the association between SPAK and barrier function in the alveolar epithelium after hyperoxic exposure.

METHODS

Hyperoxic acute lung injury (HALI) was induced by exposing mice to > 99% oxygen for 64 h. The mice were randomly allotted into four groups comprising two control groups and two hyperoxic groups with and without SPAK knockout. Mouse alveolar MLE-12 cells were cultured in control and hyperoxic conditions with or without SPAK knockdown. Transepithelial electric resistance and transwell monolayer permeability were measured for each group. In-cell western assay was used to screen the possible mechanism of p-SPAK being induced by hyperoxia.

RESULTS

Compared with the control group, SPAK knockout mice had a lower protein level in the bronchoalveolar lavage fluid in HALI, which was correlated with a lower extent of TJ disruption according to transmission electron microscopy. Hyperoxia down-regulated claudin-18 in the alveolar epithelium, which was alleviated in SPAK knockout mice. In MLE-12 cells, hyperoxia up-regulated phosphorylated-SPAK by reactive oxygen species (ROS), which was inhibited by indomethacin. Compared with the control group, SPAK knockdown MLE-12 cells had higher transepithelial electrical resistance and lower transwell monolayer permeability after hyperoxic exposure. The expression of claudin-18 was suppressed by hyperoxia, and down-regulation of SPAK restored the expression of claudin-18. The process of SPAK suppressing the expression of claudin-18 and impairing the barrier function was mediated by p38 mitogen-activated protein kinase (MAPK).

CONCLUSIONS

Hyperoxia up-regulates the SPAK-p38 MAPK signal pathway by ROS, which disrupts the TJ of the alveolar epithelium by suppressing the expression of claudin-18. The down-regulation of SPAK attenuates this process and protects the alveolar epithelium against the barrier dysfunction induced by hyperoxia.

Correlation between Claudin-18 expression and clinicopathological features and prognosis in patients with gastric cancer

BACKGROUND

To investigate the correlation between Claudin-18 expression and the clinicopathological features and prognosis of gastric cancer.

METHODS

A total of 63 patients who underwent gastric cancer surgery from December 2012 to June 2013 were recruited as the research participants. The clinicopathological data and prognostic information of the participants were collected, and expression levels of Claudin-18 in gastric cancer and adjacent tissues were detected by immunohistochemical (IHC) staining. The correlation between Claudin-18 expression and clinicopathological features of gastric cancer patients was analyzed. The Cox regression model was used to analyze the risk factors associated with the prognosis of gastric cancer patients.

RESULTS

The expression of Claudin-18 was positive in 35 (55.6%) of the participants' gastric cancer tissues, which was significantly lower than that in the adjacent tissues (51 tissues/81.0%), and the difference was statistically significant (P=0.002). In addition, the IHC staining score of Claudin-18 expression in gastric cancer tissues (1.49±1.69), was significantly lower than that in the adjacent tissues (4.61±1.81), and the difference was statistically significant (P=0.016), The incidence of nerve invasion in patients with low expression of Claudin-18 was significantly higher than that in patients with high expression of Claudin-18 (P=0.038). In addition, univariate Cox regression analysis showed that nerve invasion, Claudin-18 staining score, tumor size, and positive count of lymph nodes were risk factors associated with the survival of gastric cancer patients. Multivariate Cox regression analysis showed that Claudin-18 staining score and tumor size were independent risk factors associated with the survival of gastric cancer patients. The overall survival (OS) of patients with low Claudin-18 staining score or larger tumor size was significantly reduced.

CONCLUSIONS

The low expression of Claudin-18 was closely related to nerve invasion in gastric cancer, which indicated the poor clinical prognosis of gastric cancer patients.

Comprehensive immunohistochemical analysis of the gastrointestinal and Müllerian phenotypes of 139 ovarian mucinous cystadenomas

Mucinous cystadenoma is one of the most common benign ovarian neoplasms. The immunophenotypes and histogenetic relationships of mucinous cystadenomas with a Müllerian-type epithelium have not been fully explored. We elucidated the direction of differentiation of the mucinous epithelium that constitutes mucinous cystadenomas. Special attention was paid to the existence of gastrointestinal (GI)-type mucinous epithelium, and its association with background Müllerian-type epithelium. Immunohistochemistry was performed in 139 cases of mucinous cystadenoma to evaluate the expression of Claudin-18 (CLDN18), a novel marker of gastric differentiation; CDX2, a marker of intestinal differentiation; and estrogen receptor (ER), a marker of Müllerian differentiation. We found that GI differentiation characterized by CLDN18 and/or CDX2 positivity was observed in mucinous epithelium of most mucinous cystadenomas (129/139 cases, 93%). In a subset of these cases, the tumor was composed of mucinous epithelium exhibiting an intermediate GI and Müllerian phenotype (CLDN18+/CDX2±/ER+). Of note, in 12 cases, a transition from background Müllerian-type epithelium to mucinous epithelium with GI differentiation was identified. A minor subset (6%) of mucinous cystadenomas was considered a pure Müllerian type because the epithelium exhibited a CLDN18-/CDX2-/ER + immunophenotype. In conclusion, mucinous cystadenomas consist of three major subtypes: GI, Müllerian, and intermediate types. Most mucinous cystadenomas are GI-type, and they should be considered a precursor of GI-type mucinous borderline tumors. The existence of intermediate-type mucinous cystadenomas, and areas of transition from Müllerian-type to GI-type epithelium suggest that GI-type mucinous epithelium can arise from Müllerian duct derivatives or surface epithelium exhibiting Müllerian metaplasia in the ovary.

Claudin-18 coupled with EGFR/ERK signaling contributes to the malignant potentials of bile duct cancer

Our recent work revealed that elevated expression of claudin-18 is involved in bile duct neoplasia. In the present study, we found that wound generation of a cell sheet de novo induced claudin-18 expression in its leading edge, coincident with high mitotic activity. We also found that the suppression of claudin-18 expression significantly reduced cell growth and invasiveness of bile duct cancer cell lines and tumorigenicity in vivo. In addition, an antibody specific to an extracellular loop of claudin-18 showed similar effects on the cells such as cell proliferation. Interestingly, treatment with epidermal growth factor (EGF) and overexpression of RAS oncogene induced claudin-18 expression by activation of extracellular signal-related kinase (ERK)1/2. Furthermore, enhanced claudin-18 expression activated ERK1/2. These findings provide evidence for an oncogenic property of claudin-18 in bile duct carcinoma cells via modulation of EGFR/ERK signaling, indicating that claudin-18 is a possible therapeutic target for this malignancy.

Immunocytochemistry for Claudin-18 and Maspin in biliary brushing cytology increases the accuracy of diagnosing pancreatobiliary malignancies

OBJECTIVE

Biliary brush cytology is an important diagnostic tool in the evaluation of pancreatobiliary malignancies. However, it is difficult to distinguish between malignant and benign cells. The present study evaluated the utility of immunocytochemical expression of Claudin-18 and Maspin in brushing cytology specimens of pancreatobiliary lesions in the diagnosis of pancreatobiliary malignancies.

METHODS

The study retrospectively assessed biliary and pancreatic duct brushing cytology specimens of 43 patients whose pancreatobiliary lesions were histologically diagnosed at the University of Miyazaki Hospital. Scanty cellularity slides and cases with no histological confirmation were excluded. Alcohol-fixed and Papanicolaou-stained slides were immunostained with monoclonal antibodies to Claudin-18 and Maspin.

RESULTS

Of the 43 patients, 35 (81.4%) were finally histologically diagnosed with invasive adenocarcinomas. The sensitivity of routine cytology for the detection of malignancy was 63%, and the specificity was 100%. The sensitivity of cytology in combination with immunocytochemical expression of Claudin-18 (89%) or Claudin-18 and/or Maspin (97%) was significantly higher than that of cytology alone (P < 0.01).

CONCLUSION

Immunocytochemical staining for Claudin-18 and Maspin improved the diagnostic sensitivity for pancreatobiliary adenocarcinomas.

Claudin-18 inhibits cell proliferation and motility mediated by inhibition of phosphorylation of PDK1 and Akt in human lung adenocarcinoma A549 cells

Abnormal expression of claudin subtypes has been reported in various cancers. However, the pathological role of each claudin has not been clarified in detail. Claudin-18 was absent in human non-small cell and small cell lung cancers, although it is expressed in normal lung tissues. Here, we examined the effect of claudin-18 expression on the expression of junctional proteins, cell proliferation, and cell motility using human lung adenocarcinoma A549 cells. Real-time PCR and western blotting showed that exogenous expression of claudin-18 had no effect on the expression of junctional proteins including claudin-1, zonula occludens-1 (ZO-1), occludin, and E-cadherin. Claudin-18 was mainly distributed in cell-cell contact areas concomitant with ZO-1. Cell proliferation was significantly decreased at 48 and 72h after seeding of claudin 18-expressing cells. Claudin-18 suppressed cell motility, whereas it increased cell death in anoikis. Claudin-18 decreased phosphorylated (p)-3-phosphoinositide-dependent protein kinase-1 (PDK1) and p-Akt levels without affecting p-epidermal growth factor receptor and p-phosphatidylinositol-3 kinase (PI3K) levels. Furthermore, claudin-18 was bound with PDK1 and suppressed the nuclear localization of PDK1. We suggest that claudin-18 suppresses the abnormal proliferation and motility of lung epithelial cells mediated by inhibition of the PI3K/PDK1/Akt signaling pathway.

Expression of claudin-7 and loss of claudin-18 correlate with poor prognosis in gastric cancer

BACKGROUND

The purpose of this study was to evaluate the expression of claudin-3, claudin-7, and claudin-18 in gastric cancer and to determine the significance of these proteins for patient outcome.

MATERIALS AND METHODS

A total of 134 samples were obtained from surgically resected specimens from patients who were diagnosed with gastric carcinoma at a single institution. Paraffin tissue sections from tissue microarray blocks were examined with immunohistochemistry for the expression of claudin-3, claudin-7, and claudin-18.

RESULTS

In normal gastric tissues, positive immunoreactivity was detected for claudin-18 but not for claudin-3 or claudin-7. Claudin-3 and claudin-7 were expressed in 25.4% and 29.9% of the gastric cancer tissues, respectively. However, 51.5% of gastric cancer tissues exhibited reduced expression of claudin-18. Claudin-7 expression was significantly lower in cases with diffuse histologic type and positive lymphatic invasion. There was a significant inverse correlation between claudin-18 expression and perineural invasion. In the survival analysis, the overall survival time was shorter in patients with claudin-7 expression than in those without claudin-7 expression. However, the overall survival was longer in patients with claudin-18 expression than in those without claudin-18 expression.

CONCLUSIONS

Our data suggest that the up-regulation of claudin-3 and claudin-7 and the down-regulation of claudin-18 may play a role in the carcinogenesis of gastric cancer. Furthermore, the expression of claudin-7 and the loss of claudin-18 may be independent indicators of a poor prognosis in patients with gastric cancer.