Myofibroblasts are important contributors to human hepatocellular carcinoma: evidence for tumor promotion by proteome profiling.

Liver cancer typically occurs with a background of chronic fibrosis, characterized by the accumulation of myofibroblast-like cells. We performed 2D-PAGE-based comparative analyses with the aim to identify proteins expressed in human hepatocellular carcinoma (HCC) tissue but not in neighboring healthy liver tissue, and to make out which cell types are responsible for the expression of proteins most characteristic for HCC. LC-MS/MS analysis of the most striking spots identified proteins that were mainly related to myofibroblast-like cells. To gain more insights into the role of these cells in their contribution to HCC, we isolated myofibroblast-like cells as well as hepatocytes, both derived from HCC tissues, and subjected them to proteome profiling based on shotgun experiments. Comparative analysis, also referring to proteome profiles of other cell types previously investigated by us, pointed again to a marked contribution of myofibroblast-like cells to HCC. Intriguingly, secretome analysis of these cells identified several growth factors that may act as tumor promoters and several proteins that have been described as potential biomarkers for HCC including dickkopf-1, connective tissue growth factor, and CXCL1. Other biomarker candidates presently identified in the secretome of myofibroblasts, including lipocalin-1 and pappalysin-1, may be selected for future clinical validation. The identification of myofibroblast-like cells as important source of tumor-promoters may open new avenues to therapeutic intervention by targeting these stroma cells in addition to the cancer cells.