Biology of Human Tumors Keratin 19, a Cancer Stem Cell Marker in Human Hepatocellular Carcinoma

Purpose:Keratin 19 (K19) is a knownmarker of poor prognosis and invasion in human hepatocellular carcinoma (HCC). However, the relationship between K19 and cancer stem cells (CSCs) is unclear. Here, we determinedwhether K19 can be used as a new CSC marker and therapeutic target in HCC. Experimental Design: HCC cell lines were transfected with a K19 promoter–driven enhanced green fluorescence protein gene. CSC characteristics, epithelial–mesenchymal transition (EMT), and TGFb/Smad signaling were examined in FACS-isolated K19þ/K19 cells. K19 and TGFb receptor 1 (TGFbR1) expression in 166 consecutive humanHCC surgical specimenswas examined immunohistochemically. Results: FACS-isolated single K19þ cells showed self-renewal and differentiation into K19 cells, whereas single K19 cells did not produce K19þ cells. K19þ cells displayed high proliferation capacity and 5-fluorouracil resistance in vitro. Xenotransplantation into immunodeficient mice revealed that K19þ cells reproduced, differentiated into K19 cells, and generated large tumors at a high frequency in vivo. K19þ cells were found to be involved in EMT and the activation of TGFb/Smad signaling, and these properties were suppressed by K19 knockdown or treatment with a TGFbR1 inhibitor. The TGFbR1 inhibitor also showed high therapeutic effect against K19þ tumor in the mouse xenograft model. Immunohistochemistry of HCC specimens showed that compared with K19 patients, K19þ patients had significantly poorer recurrencefree survival and higher tumor TGFbR1 expression. Conclusions: K19 is a new CSC marker associated with EMT and TGFb/Smad signaling, and it would thus be a good therapeutic target for TGFbR1 inhibition. Clin Cancer Res; 21(13);