title: A role for ABCG2 beyond drug transport: Regulation of autophagy.
abstract: The ABC drug transporters, including ABCG2, are well known for their ability to efflux a wide spectrum of chemotherapeutic agents, thereby conferring a multidrug-resistant phenotype. However, studies over the past several years suggest that the ABC transporters may play additional role(s) in cell survival in the face of stress inducers that are not ABCG2 substrates (i.e., nutrient deprivation, ionizing radiation, rapamycin). The mechanism by which this occurs is largely unknown. In the present study, using several cancer cell lines and their ABCG2-overexpressing sublines, we show that cells overexpressing ABCG2 were more resistant to these stressors. This resistance was associated with an elevated level of autophagy flux, as measured by a higher rate of SQSTM1/p62 degradation and greater accumulation of LC3-II when compared to parental cells. Knockdown of ABCG2 reduced autophagic activity in resistant cells to a level similar to that observed in parental cells, confirming that the enhanced autophagy was ABCG2-dependent. Moreover, using cell viability, apoptosis, and clonogenic assays, we demonstrated that the ABCG2-expressing cells were more resistant to amino acid starvation and radiation-induced cell death. Importantly, knockdown of the critical autophagy factors ATG5 and ATG7 greatly reduced cell survival, verifying that enhanced autophagy was critical for this effect. Taken together, these data indicate that autophagy induced by various stressors is enhanced/accelerated in the presence of ABCG2, resulting in delayed cell death and enhanced cell survival. This defines a new role for this transporter, one with potential clinical significance.
authors.affiliation: a Cancer Institute of New Jersey and Robert Wood Johnson Medical School, Rutgers, State University of New Jersey , New Brunswick , NJ , USA.
authors.forename: Rui
authors.initials: R
authors.lastname: Ding
authors.affiliation: a Cancer Institute of New Jersey and Robert Wood Johnson Medical School, Rutgers, State University of New Jersey , New Brunswick , NJ , USA.
authors.forename: Shengkan
authors.initials: S
authors.lastname: Jin
authors.affiliation: a Cancer Institute of New Jersey and Robert Wood Johnson Medical School, Rutgers, State University of New Jersey , New Brunswick , NJ , USA.
authors.forename: Kirk
authors.initials: K
authors.lastname: Pabon
authors.affiliation: a Cancer Institute of New Jersey and Robert Wood Johnson Medical School, Rutgers, State University of New Jersey , New Brunswick , NJ , USA.
authors.forename: Kathleen W
authors.initials: KW
authors.lastname: Scotto
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2 / Q000235:genetics / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D001343:Autophagy / Q000187:drug effects*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000494:pharmacology
chemical_list: C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D000970:Antineoplastic Agents; D008869:Microtubule-Associated Proteins; D009363:Neoplasm Proteins; D034741:RNA, Small Interfering
keywords: ABC transporters; ABCG2; BCRP; amino acid starvation; autophagy; drug transporters; multidrug resistance; radiation; tumor cell survival