Abstract 2408: CD44s is required for a tumor-initiating stem-like mesenchymal phenotype in hepatocellular carcinoma via ligand-independent c-Met activation

Abstract

Abstract c-Met, a high affinity receptor for hepatocyte growth factor (HGF), plays a critical role in cancer growth, invasion and metastasis. Hepatocellular carcinoma (HCC) patients with active HGF/c-Met signaling have a significantly worse prognosis. CD44, the receptor for hyaluronic acid, is utilized as a surface marker to identify mesenchymal tumor-initiating stem-like cells (TISC) in several cancers. CD44v6 (spice variant 6) has been shown to promote HGF activation of c-Met. In this work, we examine the role of CD44s as a deregulator and activator of c-Met signaling in HCC. In a transcriptome profile analysis of 149 human HCC cases, we identified a significant positive correlation (R2=0.8993) between up-regulated CD44 and c-Met expression. The human HCC cell lines MHCC97-H and Huh7 were further utilized to investigate the direct relationship between c-Met and CD44s. Metastatic MHCC97-H cells are 95% CD44+ and demonstrate ligand-independent c-Met activation. CD44+/c-Met+ MHCC97-H cells demonstrate a mesenchymal phenotype with low expression of E-cadherin, high level of tumorsphere formation, increased expression of fibronectin and Zeb2 compared to Huh7 cells, which have are CD44neg/c-Metneg. In MHCC97-H cells, a direct interaction between CD44s and c-Met was demonstrated by immunoprecipitation/immuno-blot analysis. Transient and stable inhibition of c-Met in MHCC97-H cells results in increased E-cadherin, decreased CD44s, and reduced tumor-initiating characteristics and loss of tumorsphere formation. Likewise, inhibition of CD44s demonstrates similar phenotype with increased E-cadherin, decreased tumorsphere formation, and decreased c-Met activation and loss of downstream Akt and Erk phosphorylation. CD44s knockdown recovered c-Met to a regulated HGF-dependent state. Selective inhibition of either PI3K (Ly294002) or MAPK (PD98059) pathways in MHCC97-H cells demonstrate that PI3K/Akt activation signals drive CD44s expression in a feed forward fashion. Conversely, the over-expression of CD44s in Huh7 cells demonstrates a mesenchymal phenotype with fibroblastic-like cell morphology, decreased E-cadherin, increased Zeb1, increased PI3K/Akt signaling, and increased tumorsphere formation compared to control Huh7 cells. Selective inhibition of PI3K/Akt signaling in CD44+ Huh7 cells resulted in reduced CD44s expression and decreased tumorsphere formation. In conclusion, CD44s induces a mesenchymal phenotype and tumor initiating characteristics in HCC through the deregulation of c-Met and activation of a positive feedback loop through PI3K/Akt signaling. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2408. doi:1538-7445.AM2012-2408