ABCG2 and glioblastoma: The SHH signaling pathway is critically implicated in the oncogenesis of GBM and the self-renewal of GSCs, as the activation of the SHH signaling pathway upregulates the drug efflux Pglycoprotein (ABCB1), ABC transporter ABCG2, multi-drug resistance-associated protein-1(ABCC1/MRP1), MGMT, B cell-specific Moloney murine leukemia virus integration site 1 (BMI1) (31, 139–141).