Abstract 989: Mild ER stress increases human ABC transporter expression and drug transport function in polarized cell monolayers.

Abstract

Abstract Expression of ATP-binding cassette (ABC) transporter genes such as MDR1 (ABCB1/P-gp) is associated with poor outcome in chemotherapy and a multidrug resistant phenotype in cancer. Endoplasmic reticulum (ER) stress has been implicated in tumor growth but its role in drug resistance remains unclear. Here, we hypothesize that ER stress could increase expression of drug efflux transporters. To test this hypothesis, we developed a transient expression system in which human ABC transporters were ectopically expressed in a cell line monolayer by the BacMam baculovirus. The baculovirus is able to infect several mammalian cell lines including LLC-PK1, T-84, and MA104 without affecting the tightness of the host cell monolayers. In LLC-PK1 cells infected by BacMam vectors, induction of mild ER stress by pre-incubation (pre-conditioning) with thapsigargin (0.5 μg/ml) or tunicamycin (1 μg/ml), which are well-characterized ER-stress inducers, increased ABCB1 (P-gp) and ABCG2 (BCRP) levels. Drug transport assays showed that P-gp expressing cells pre-conditioned with thapsigargin showed increased directional transport of [3H] paclitaxel across the cell monolayer. The effect of thapsigargin was inhibited by the presence of the Erk inhibitor PD098059 but not the P38(MAPK) inhibitor SB203580, or the phosphatidylinositol 3-kinase (PI3-kinase) inhibitor LY294002, suggesting that expression of ABC transporter is influenced by mild ER stress response and, at least in part, by the ERK/MAPK signaling pathway. Although pre-conditioning with tunicamycin can increase P-gp expression, it also inhibits N-glycosylation of P-gp. Collectively, our findings indicate that mild ER stress responses up-regulate drug transporters introduced into cells by BacMam vectors. Citation Format: King Leung Fung, Jessica Pixley, Darrell J. Talbert, Khyati Kapoor, Suresh Ambudkar, Michael M. Gottesman. Mild ER stress increases human ABC transporter expression and drug transport function in polarized cell monolayers. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 989. doi:10.1158/1538-7445.AM2013-989