ABCG2 and breast cancer: Lastly, Das et al. reported that osteopontin (OPN), a bone matrix protein, non-canonically activates GLI1 via GSK3β inhibition to promote GLI1 nuclear translocation and GLI1-dependent upregulation of ABC transporters (ABCB1 and ABCG2) and consequently drug resistance to doxorubicin, paclitaxel, and cisplatin by reducing intracellular drug retention in breast cancer cell lines [126].