The MET oncogene is a functional marker of a glioblastoma stem cell subtype and drives the invasive phenotype

Eighteen independent neurospheres derived from patients affected by primary glioblastoma were grouped into “classical”, “mesenchymal” or “proneural” subtypes according to analysis of genetic lesions and gene expression profiling. Here we show that expression of the MET oncogene, encoding the tyrosine kinase receptor for HGF, associates with mesenchymal and proneural neurospheres (Met-pos-NS). Met expression is almost absent from classical neurospheres (Met-neg-NS), and mutually exclusive with amplification and expression of the EGF receptor gene. Met-pos-NS and Met-neg-NS display distinct growth factor requirements, differentiate along divergent pathways, and generate tumors with distinctive histological features. Met-pos-NS contain a variable percentage of Met positive (Methigh) and Met negative (Metneg) cells. After purification, only Methigh cells display clonogenic ability in vitro, and regenerate neurospheres containing both Methigh and Metneg cells. After in vivo transplantation, Methigh cells display highly enriched tumorigenic potential as compared with Metneg cells. At functional level, in Methigh cells, HGF concomitantly sustains proliferation, clonogenicity, expression of self-renewal markers, migration and invasion. These data show that Met is a functional marker of glioblastoma stem cells, and a candidate target for molecular diagnosis and therapy of a glioblastoma subset. 37 samples (17 replicate samples and 1 triplicate sample)