Changes in protein expression in two cholangiocarcinoma cell lines undergoing formation of multicellular tumor spheroids in vitro

Epithelial-to-Mesenchymal Transition (EMT) is relevant in malignant growth and frequently correlates with worsening disease progression due to its implications in metastases and resistance to therapeutic interventions. Although EMT is known to occur in several types of solid tumors, the information concerning tumors arising from the epithelia of the bile tract is still limited. In order to approach the problem of EMT in cholangiocarcinoma, we decided to investigate the changes in protein expression occurring in two cell lines under conditions leading to growth as adherent monolayers or to formation of multicellular tumor spheroids (MCTS), which are considered culture models that better mimic the growth characteristics of in-vivo solid tumors. In our system, changes in phenotypes occur with only a decrease in transmembrane E-cadherin and vimentin expression, minor changes in the transglutaminase protein/activity but with significant differences in the proteome profiles, with declining and increasing expression in 6 and in 16 proteins identified by mass spectrometry. The arising protein patterns were analyzed based on canonical pathways and network analysis. These results suggest that significant metabolic rearrangements occur during the conversion of cholangiocarcinomas cells to the MCTS phenotype, which most likely affect the carbohydrate metabolism, protein folding, cytoskeletal activity, and tissue sensitivity to oxygen.