CD44 is required for two consecutive steps in HGF/c-Met signaling.
ABSTRACT The tyrosine kinase receptor c-Met and its ligand HGF/SF, ezrin, and splice variants of CD44 have independently been identified as tumor metastasis-associated proteins. We now show that these proteins cooperate. A CD44 isoform containing variant exon v6 sequences is strictly required for c-Met activation by HGF/SF in rat and human carcinoma cells, in established cell lines as well as in primary keratinocytes. CD44v6-deficient tumor cells were unable to activate c-Met unless they were transfected with a CD44v6-bearing isoform. Antibodies to two v6-encoded epitopes inhibited autophosphorylation of c-Met by interfering with the formation of a complex formed by c-Met, CD44v6, and HGF/SF. In addition, signal transduction from activated c-Met to MEK and Erk required the presence of the cytoplasmic tail of CD44 including a binding motif for ERM proteins. This suggests a role for ERM proteins and possibly their link to the cortical actin cytoskeleton in signal transfer.
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ABSTRACT: In the last decade, the tyrosine kinase receptor cMET, together with its ligand hepatocyte growth factor (HGF), has become a target in non-small cell lung cancer (NSCLC). Signalization via cMET stimulates several oncological processes amongst which are cell motility, invasion and metastasis. It also confers resistance against several currently used targeted therapies, e.g., epidermal growth factor receptor (EGFR) inhibitors. In this review, we will discuss the basic structure of cMET and the most important signaling pathways. We will also look into aberrations in the signaling and the effects thereof in cancer growth, with the focus on NSCLC. Finally, we will discuss the role of cMET as resistance mechanism.03/2015; 7(2):556-573. DOI:10.3390/cancers7020556
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ABSTRACT: The difficulty in expanding cancer-initiating cells in vitro is one of major obstacles for their biochemical characterization. We found that Rho kinase (ROCK) inhibitors as well as blebbistatin, a myosin II inhibitor, greatly facilitated the establishment of spheroids from primary colon cancer. The spheroid cells expressed cancer stem cell markers, showed the ability to differentiate, and induced tumors in mice. The spheroids were composed of cells that express various levels of CD44, whereas CD44(high) cells were associated with increased sphere-forming ability, expression of the activating form of beta-catenin, and elevated levels of glycolytic genes, CD44(-/low) cells showed increased levels of differentiation markers and apoptotic cells. The spheroid cells expressed variant forms of CD44 including v6, and the induction of the variants was associated with the activating phosphorylation of c-Met. As expected from the predicted hierarchy, CD44(high) cells differentiated into CD44(-/low) cells. Unexpectedly, a fraction of CD44(-/low) cells generated CD44(high) cells, and the ROCK inhibitor or blebbistatin primed the transition by inducing CD44 expression. We propose that the transition from CD44(-/low) to CD44(high) state helps to maintain a CD44(high) fraction and the tumorigenic diversity in colon cancer. Cancer Res; 72(19); 5101-10. (C) 2012 AACR.Cancer Research 09/2012; 72(19):5101-5110. DOI:10.1158/0008-5472.CAN-11-3812 · 9.28 Impact Factor