SMAD2 and glioblastoma: Mechanistically, TGF-β has been proposed to induce a mesenchymal phenotype in GBM cells through the activation of SMAD2 and ZEB1 (a TGF-β cytoplasmic signal transducer and a known transcriptional inducer of EMT, respectively, [91]) resulting in enhanced migration and invasion capacities of GSCs [92].