Cholangiocarcinoma (CCA), a malignant tumor derived from bile duct epithelium, occurs with a higher incidence in tropical countries, such as Thailand. Distinguishing CCA from hepatocellular carcinoma (HCC) of the liver often requires the use of histochemistry, so molecular markers for diagnosis and prognosis are still required. In this study, the two-dimensional (2-D) protein map of a Thai human bile duct epithelial carcinoma cell line (HuCCA-1) has been compared to human hepatocellular carcinoma cell lines (HepG2 and HCC-S102) and a human breast epithelial cancer cell line (MCF-7). Our results show that HuCCA-1 expressed a unique pattern of proteins. Forty-three major proteins were identified by matching to the map of MCF-7, and by matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) and electrospray ionization-tandem MS (ESI-MS/MS). Cytokeratins CK8 and CK18 were overexpressed in both HuCCA-1 and HCC, while CK7 and CK19 were only expressed in HuCCA-1. Four specific proteins with MW/pI 57.2/5.21 (U1, vimentin), 42.2/6.20 (U2), 43.2/6.20 (U3, EF-TU), and 42.2/6.40 (U4, unidentified) were absent from HepG2. U2 showed high expression in HuCCA-1, while U1 and U4 showed high expression in HCC-S102. U2 could be separated in 2 proteins, U2/1 (alpha-enolase) and U2/2 (not identified) by using IPG pH 4-7. Galectin-3 showed high expression level in HuCCA-1 by 1-DE immunodetection, and gave only one spot with MW 32.9 kDa and pI 8.29 on 2-DE immunoblotting, Thus, certain proteins, namely CK7, CK19, U2/2 and galectin-3, may be good markers useful for differential diagnosis of cholangiocarcinoma compared to hepatocellular carcinoma.

It is now widely accepted that the tumor microenvironment influences the fate of cancer cells and plays crucial roles in regulating tumor dormancy and chemoresistance. The standard cell culture system on plastic surfaces does not account for cell interactions with the extracellular matrix (ECM), and is thus a less reliable approach to analyze cellular activity ex vivo. In the present study, A549 lung cancer cells were cultured in a semi-solid growth substrate (Matrigel) to mimic the tumor microenvironment and to investigate the role played by ECM proteins, as well as to evaluate the mechanism of cell-ECM communication. A549 cells embedded in semi-solid Matrigel exhibited dormant cell characteristics, including decreased cell proliferation, migration and invasion rates, compared with the corresponding cells cultured on plastic plates. Exposure of A549 cells to Matrigel leads to resistance against conventional chemotherapeutic drugs (etoposide, paclitaxel, vinblastine, doxorubicin and 2-deoxy-D-glucose). Cell cycle distribution analysis indicated that a larger percentage of the cells embedded within semi-solid Matrigel was arrested in the G0/G1 phase. RT-qPCR analysis revealed that A549 cells cultured in semi-solid Matrigel exhibited a marked decrease in the expression levels of genes that are related to tumor progression and invasion (uPA, uPAR, MMP2, MMP7, MMP9 and CXCR4). The effects of altering various signaling pathways, such as p-ERK, p-Akt and p-STAT3, were evaluated, in order to assess whether these pathways could account for the observed responses of the cells. The inhibition of ERK1/2 and Akt activation using specific inhibitors induced G0/G1 arrest and drug resistance. These results demonstrated that Matrigel drove A549 cells into a drug-resistant dormancy state, most likely through inhibition of the ERK1/2 and PI3K/Akt pathways. Cell culture within semi-solid Matrigel offered a simple in vitro model for studying the mechanisms responsible for tumor dormancy and drug resistance. These studies may lead to therapeutic approaches that can eliminate dormant tumor cells and prevent disease recurrence.

Cholangiocarcinoma is a malignant biliary tract tumor with an extremely poor prognosis. CD24 expression has been linked to the aggressiveness of cholangiocarcinoma cells and the adverse prognosis of cholangiocarcinoma patients. In the present study, the underlying mechanism of aggressive CD24+ cholangiocarcinoma cell behavior was elucidated. The magnetic-activated cell sorting system was used to isolate CD24+ and CD24− cell populations from RMCCA1 cholangiocarcinoma cells. Using a human tumor metastasis PCR array, it was observed that numerous tumor-associated genes were upregulated in the CD24+ cells, including CXC chemokine receptor type 4 (CXCR4). In addition, an intracellular signaling array demonstrated the activation of extracellular signal-regulated kinase (ERK)1/2, which is downstream of the CXCR4 signaling cascade, in the CD24+ cells. Inhibition of CXCR4 or ERK1/2 significantly inhibited the motility and invasiveness of the CD24+ cells. The present study indicates that CXCR4 and ERK1/2 are induced by CD24 and that these proteins are associated with cholangiocarcinoma cell invasion.

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