Expression of KL-6 mucin, a human MUC1 mucin, in intrahepatic cholangiocarcinoma and its potential involvement in tumor cell adhesion and invasion

Research progress of KL-6 in respiratory system diseases

This article comprehensively elucidates the discovery of Krebs von den Lungen-6 (KL-6), its structural features, functional mechanisms, and the current research status in various respiratory system diseases. Discovered in 1985, KL-6 was initially considered a tumor marker, but its elevated levels in interstitial lung disease (ILD) led to its recognition as a relevant serum marker for ILD. KL-6 is primarily produced by type 2 alveolar epithelial cell regeneration. Over the past 30 years since the discovery of KL-6, the number of related research papers has steadily increased annually. Following the coronavirus disease 2019 (COVID-19) pandemic, there has been a sudden surge in relevant literature. Despite KL-6's potential as a biomarker, its value in the diagnosis, treatment, and prognosis varies across different respiratory diseases, including ILD, idiopathic pulmonary fibrosis (IPF), COVID-19, and lung cancer. Therefore, as an important serum biomarker in respiratory system diseases, the value of KL-6 still requires further investigation.

Diagnostic Value of Serum KL-6 in Interstitial Lung Diseases

Objective

To explore serum KL-6 level and investigate its diagnostic value in interstitial lung diseases (ILDs).

Methods

Serum KL-6 level was measured using the chemiluminescent enzyme immunoassay. Statistical analysis was performed for determining the KL-6 concentration of each group.

Results

KL-6 level (U/mL) in the ILD group was 1388.321 ±1943.116, which was higher than that in the control group, showing a significant statistical difference. ROC curve analysis based on the receiver operating characteristic curve showed the optimal cut-off value of 402.5U/mL, sensitivity of 77.4%, specificity of 93.4%, and accuracy of 89.4%; through Chi-square test with the two groups, the positive rate of KL-6 in patients with ILD was proved to be significantly higher than that in the control group. KL-6 level was 1063.00±504.757 in the idiopathic pulmonary fibrosis (IPF) group, 1346.892 ±1827.252 in the connective tissue disease-associated interstitial lung disease (CTD-ILD) group, 467.889±288.859 in the organizing pneumonia (OP) group, 8252.333±6050.625 in the pulmonary alveolar proteinosis (PAP) group, and 359.200±392.707 in the sarcoidosis group. The rank sum test showed that the differences were statistically significant. KL-6 level was the lowest in the sarcoidosis group, followed by that in the OP group.

Conclusion

Serum KL-6 level was confirmed to be highly sensitive, specific, and accurate in the diagnosis of ILD. Subgroup analysis showed that the KL-6 level was the lowest in the sarcoidosis group, followed by that in the OP group.

Novel approaches in search for biomarkers of cholangiocarcinoma

Cholangiocarcinoma (CCA) arises from the ductular epithelium of the biliary tree, either within the liver (intrahepatic CCA) or more commonly from the extrahepatic bile ducts (extrahepatic CCA). This disease has a poor prognosis and a growing worldwide prevalence. The poor outcomes of CCA are partially explained by the fact that a final diagnosis is challenging, especially the differential diagnosis between hepatocellular carcinoma and intrahepatic CCA, or distal CCA and pancreatic head adenocarcinoma. Most patients present with an advanced disease, unresectable disease, and there is a lack in non-surgical therapeutic modalities. Not least, there is an acute lack of prognostic biomarkers which further complicates disease management. Therefore, there is a dire need to find alternative diagnostic and follow-up pathways that can lead to an accurate result, either singlehandedly or combined with other methods. In the "-omics" era, this goal can be attained by various means, as it has been successfully demonstrated in other primary tumors. Numerous variants can reach a biomarker status ranging from circulating nucleic acids to proteins, metabolites, extracellular vesicles, and ultimately circulating tumor cells. However, given the relatively heterogeneous data, extracting clinical meaning from the inconsequential noise might become a tall task. The current review aims to navigate the nascent waters of the non-invasive approach to CCA and provide an evidence-based input to aid clinical decisions and provide grounds for future research.

Alpha-Fetoprotein Binding Mucin and Scavenger Receptors: An Available Bio-Target for Treating Cancer

Alpha-fetoprotein (AFP) entrance into cancer cells is mediated by AFP receptors (AFPRs) and exerts malignant effects. Therefore, understanding the structure of AFPRs will facilitate the development of rational approaches for vaccine design, drug delivery, antagonizing immune suppression and diagnostic imaging to treat cancer effectively. Throughout the last three decades, the identification of universal receptors for AFP has failed due to their complex carbohydrate polymer structures. Here, we focused on the two types of binding proteins or receptors that may serve as AFPRs, namely, the A) mucin receptors family, and B) the scavenger family. We presented an informative review with detailed descriptions of the signal transduction, cross-talk, and interplay of various transcription factors which highlight the downstream events following AFP binding to mucin or scavenger receptors. We mainly explored the underlying mechanisms involved mucin or scavenger receptors that interact with AFP, provide more evidence to support these receptors as tumor AFPRs, and establish a theoretical basis for targeting therapy of cancer.

Mucins: the Old, the New and the Promising Factors in Hepatobiliary Carcinogenesis

Mucins are large O-glycoproteins with high carbohydrate content and marked diversity in both the apoprotein and the oligosaccharide moieties. All three mucin types, trans-membrane (e.g., MUC1, MUC4, MUC16), secreted (gel-forming) (e.g., MUC2, MUC5AC, MUC6) and soluble (non-gel-forming) (e.g., MUC7, MUC8, MUC9, MUC20), are critical in maintaining cellular functions, particularly those of epithelial surfaces. Their aberrant expression and/or altered subcellular localization is a factor of tumour growth and apoptosis induced by oxidative stress and several anti-cancer agents. Abnormal expression of mucins was observed in human carcinomas that arise in various gastrointestinal organs. It was widely believed that hepatocellular carcinoma (HCC) does not produce mucins, whereas cholangiocarcinoma (CC) or combined HCC-CC may produce these glycoproteins. However, a growing number of reports shows that mucins can be produced by HCC cells that do not exhibit or are yet to undergo, morphological differentiation to biliary phenotypes. Evaluation of mucin expression levels in precursors and early lesions of CC, as well as other types of primary liver cancer (PLC), conducted in in vitro and in vivo models, allowed to discover the mechanisms of their action, as well as their participation in the most important signalling pathways of liver cystogenesis and carcinogenesis. Analysis of mucin expression in PLC has both basic research and clinical value. Mucins may act as oncogenes and tumour-promoting (e.g., MUC1, MUC13), and/or tumour-suppressing factors (e.g., MUC15). Given their role in promoting PLC progression, both classic (MUC1, MUC2, MUC4, MUC5AC, MUC6) and currently tested mucins (e.g., MUC13, MUC15, MUC16) have been proposed to be important diagnostic and prognostic markers. The purpose of this review was to summarize and update the role of classic and currently tested mucins in pathogenesis of PLC, with explaining the mechanisms of their action in HCC carcinogenesis. It also focuses on determination of the diagnostic and prognostic role of these glycoproteins in PLC, especially focusing on HCC, CC and other hepatic tumours with- and without biliary differentiation.

Diagnostic usefulness of KL-6 concentration of bile in biliary tract cancer

The sensitivity of bile cytology for biliary tract cancer varies from 6-64%, and hence remains unsatisfactory. Sialylated carbohydrate antigen KL-6 mucin is positive in biliary tract cancer tissues and serum KL-6 levels are significantly increased in intrahepatic ductal adenocarcinoma patients compared with healthy individuals. The aim of the present study was to evaluate the usefulness of the KL-6 concentration of bile for the diagnosis of biliary tract cancer. Bile cytology and measurements of bile KL-6 concentration were conducted for 43 patients (25 biliary tract cancers and 18 benign biliary disease). The concentration of KL-6 in the bile of the biliary tract cancer group was compared with the benign biliary disease group. The diagnostic ability was assessed by using receiver operating characteristic curves (ROC). The mean KL-6 concentration of bile for biliary tract cancer (34.6±51.6 U/ml) was increased compared with benign biliary disease (5.2±3.9 U/ml, P<0.001). The area under the ROC for diagnosis of biliary tract cancer was 0.84 for benign biliary disease. When the cut-off level of the KL-6 concentration of bile was 8.6 U/ml, the sensitivity, specificity, and accuracy of the KL-6 concentration of bile alone for the diagnosis of biliary tract cancer were 72, 89, and 79%, respectively. Adding the bile KL-6 concentration to bile cytology measurements, the sensitivity for the diagnosis of biliary tract cancer was increased significantly (100%, P=0.0184). The KL-6 concentration of bile may strengthen the sensitivity of bile cytology for biliary tract cancer.

Inhibition of KL-6/MUC1 glycosylation limits aggressive progression of pancreatic cancer

AIM: To evaluate the significance of KL-6/MUC1 (a type of MUC1) glycosylation in pancreatic cancer progression.

METHODS: KL-6/MUC1 expression was detected by immunohistochemistry in 48 patients with pancreatic duct cell carcinoma. The N-/O-glycosylation inhibitors (tunicamycin and benzyl-N-acetyl-α-galactosaminide) were then used to interfere with KL-6/MUC1 glycosylation in two pancreatic carcinoma cell lines, and the effects on KL-6/MUC1 expression, and cell adhesion and invasion were determined. In addition, protein expression of epithelial-mesenchymal transition markers, E-cadherin and vimentin, were evaluated in cells after treatment with glycosylation inhibitors.

RESULTS: Overexpression of KL-6/MUC1 was found in all pancreatic cancer tissues, but not in the surrounding normal pancreatic tissues. The expression profile of KL-6/MUC1 was significantly decreased after treatment with the inhibitors. The adhesion and invasive ability of cancer cells were significantly decreased after drug treatment, and increased E-cadherin and decreased vimentin expression were found.

CONCLUSION: KL-6/MUC1 glycosylation is involved in pancreatic cancer metastasis and invasion. Therapeutic strategies which target this may help control the aggressive behavior of pancreatic cancer cells.

Involvement of estrogen in gastric cancer cell invasion regulated by tunicamycin induced-endoplasmic reticulum stress

AIM: To investigate the involvement of estrogen in gastric cancer cell invasion regulated by tunicamycin (TM) induced-endoplasmic reticulum stress and to explore the possible mechanism involved.

METHODS: TM (3 μmol/L) alone or in combination with 17β-estradiol (E2, 10-9 mol/L) was incubated with SGC7901 cells for 24 h, with the same concentrations of DMSO and alcohol used as vehicle controls. After treatment, the invasion of gastric cancer cells was evaluated by Transwell chamber assays. The expression of phosphorylated protein kinase RNA-like endoplasmic reticulum kinase (pPERK) and phosphorylated glycogen synthase kinase-3β (GSK-3β) at Ser9 were examined by Western blot analysis.

RESULTS: TM induced-endoplasmic reticulum stress, which was demonstrated by increased pPERK, decreased the invasion ability of gastric cancer SGC7901 cells and the phosphorylation of GSK-3β at Ser9. However, simultaneous treatment with E2 increased the invasion of gastric cancer cells by counteracting the activating effect of TM on GSK-3β, causing an increase in the phosphorylation of Ser9-GSK-3β.

CONCLUSION: Estrogen may counteract endoplasmic reticulum stress-induced activation of GSK-3β and increase the invasion of gastric cancer cells.

Involvement of tunicamycin-induced endoplasmic reticulum stress in invasion of gastric cancer cells

AIM: To investigate the involvement of tunicamycin (TM)-induced endoplasmic reticulum stress in the invasion of gastric cancer cells and the underlying mechanisms.

METHODS: SGC7901 cells were treated with TM at a concentration of 3 μmol/L for 24 h. After treatment, the invasion of gastric cancer cells was evaluated by Transwell chamber assay. The phosphorylation of protein kinase RNA-like endoplasmic reticulum kinase (pPERK) and glycogen synthase kinase-3β (GSK-3β) at Ser9 was examined by Western blot.

RESULTS: TM treatment induced endoplasmic reticulum stress, which was demonstrated by increased pPERK. Endoplasmic reticulum stress decreased the invasion ability of gastric cancer cells and the phosphorylation of GSK-3β at Ser9.

CONCLUSION: Endoplasmic reticulum stress induced by TM may decrease the invasion of gastric cancer cells by activation of GSK-3β.

Expression of KL-6/MUC1 in pancreatic ductal carcinoma and its potential relationship with β-catenin in tumor progression

AIM

The aim of this study was to evaluate the expression of Krebs yon den Lundgen-6/Mucin 1 (KL-6/MUC1) in pancreatic ductal carcinoma and its potential relationship with β-catenin in tumor progression.

MAIN METHODS

The expressions of KL-6/MUC1 and β-catenin in 18 cases of pancreatic ductal carcinoma were detected by immunohistochemical staining. To determine the impact of KL-6/MUC1 down-regulation on pancreatic ductal carcinoma progression, siRNA targeting MUC1 was used to knockdown KL-6/MUC1 expression. The down-regulation of KL-6/MUC1 expression was confirmed by reverse transcription-polymerase chain reaction and immunofluorescence staining. E-cadherin and E-cadherin/β-catenin complex expressions were determined by immunoprecipitation. The expressions of KL-6/MUC1, β-catenin, cyclin D1 and c-myc were detected by Western blot. Cell proliferation, apoptosis and invasive abilities were detected by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide assay, Annexin V-FITC apoptosis detection kit and invasion assay.

KEY FINDINGS

Positive KL-6/MUC1 staining was observed in the cancer tissues of all the 18 pancreatic ductal carcinoma cases (100.0%), and high nuclear β-catenin expression was seen in 12 cancers (66.7%). Reverse transcription-polymerase chain reaction and immunofluorescence staining showed that both KL-6/MUC1 mRNA and protein were effectively silenced by MUC1 siRNA. After KL-6/MUC1 knockdown, E-cadherin and E-cadherin/β-catenin complex expressions were increased, while the nuclear β-catenin, cyclin D1, and c-myc expressions were decreased. Down-regulation of KL-6/MUC1 also resulted in slower proliferation, increased apoptosis and decreased invasive ability.

SIGNIFICANCE

This study indicated that KL-6/MUC1 played a complex role in regulating pancreatic ductal carcinoma cell proliferation, apoptosis, and invasion, and also supported the hypothesis that there is a functional link between KL-6/MUC1 expression and β-catenin subcellular localization.

Application of nucleic acid aptamers for digestive disease research

Nucleic acid aptamers, selected from a synthesized library of random single-stranded oligonucleotides by systematic evolution of ligands by exponential enrichment (SELEX), are oligonucleotide ligands binding to target molecules with high specificity and affinity. Nucleic acid aptamers have similar functions to antibodies, but possess the advantages of wider range of targets, better stability, easier modification and synthesis, showing promising prospects for diagnosis and treatment of diseases. In terms of digestive diseases, nucleic acid aptamers have been applied in the research of tumor markers, anti-tumor therapy, hepatitis virus C and liver imaging.