E2F1 and glioblastoma: In support for a cause-effect relationship between GLI inhibition and the reduction in USP48 and iASSP mRNA levels, USP48 was found to be a direct transcriptional target of GLI1 in glioblastoma cells (39), and iASPP to be induced by GLI1/2 activation via E2F1 in melanoma cells (39, 41).