Porcelli Letizia, Giovannetti Elisa, Assaraf Yehuda G, Jansen Gerrit, Scheffer George L, Kathman Ietje, Azzariti Amalia, Paradiso Angelo, Peters Godefridus J
National Cancer Institute Giovanni Paolo II: Viale Orazio Flacco, 65, 70124 Bari, Italy.
Curr Drug Targets. 2014;15(14):1322-30. doi: 10.2174/1389450116666141205145620.
While multidrug resistance (MDR) in cancer is well established, little is known about the cellular pathways regulating the expression and trafficking of the MDR efflux transporter like BCRP (ABCG2). Here we evaluated the role of signalling downstream of EGFR on BCRP expression and sub-cellular localization using lung cancer cells harboring BCRP but expressing various EGFR and Ras activating mutations; A549 (K-Ras-G12S), H292 wild-type EGFR and Ras, and H1650 (EGFR-DelE747-A750). Immunocytochemistry and immunofluorescence studies demonstrated that BCRP was predominantly intracellular but its expression was found also on the plasma membrane in A549 and H1650 cells with activated Ras and EGFR. Remarkably, EGFR inhibition by erlotinib at IC₅₀ concentrations induced a differential timedependent alteration in BCRP gene and protein expression. In H1650 cells, erlotinib enhanced both the total and plasma membrane degradation of BCRP by ubiquitination within 6-24 hours, whereas BCRP expression regained the original basal levels after 48 hours. In erlotinib treated H292 cells, BCRP levels decreased at 24 hours until 72 hours, whereas in A549 cells erlotinib initially reduced BCRP expression but then induced its accumulation on the plasma membrane at 72 hours. We further found that the PI3K/Akt inhibitor LY294002 down-regulated BCRP expression, hence showing that the Akt pathway is involved in the regulation of BCRP expression but not in its localization in these lung cancer cell lines. Finally, the selective BCRP transport inhibitor Ko143 did not increase erlotinib sensitivity, but did decrease the transport activity of BCRP in A549 and H1650 cells as it induced the accumulation of its transport substrate topotecan. In conclusion, our results suggest that the EGFR and Akt pathways are involved in regulation of BCRP expression, trafficking and drug transport activity. These findings warrant future studies on the pharmacologic modulation of these pathways to enhance the efficacy of anticancer combinations of erlotinib with drugs that are BCRP transport substrates.
虽然癌症中的多药耐药性（MDR）已得到充分证实，但对于调节BCRP（ABCG2）等MDR外排转运蛋白表达和转运的细胞途径却知之甚少。在这里，我们使用携带BCRP但表达各种EGFR和Ras激活突变的肺癌细胞，评估了EGFR下游信号传导对BCRP表达和亚细胞定位的作用；A549（K-Ras-G12S）、H292野生型EGFR和Ras以及H1650（EGFR-DelE747-A750）。免疫细胞化学和免疫荧光研究表明，BCRP主要位于细胞内，但在Ras和EGFR激活的A549和H1650细胞的质膜上也发现了其表达。值得注意的是，厄洛替尼在IC₅₀浓度下对EGFR的抑制作用诱导了BCRP基因和蛋白表达的不同时间依赖性改变。在H1650细胞中，厄洛替尼在6至24小时内通过泛素化增强了BCRP的总降解和质膜降解，而48小时后BCRP表达恢复到原始基础水平。在厄洛替尼处理的H292细胞中，BCRP水平在24小时至72小时内下降，而在A549细胞中，厄洛替尼最初降低了BCRP表达，但在72小时时诱导其在质膜上积累。我们进一步发现PI3K/Akt抑制剂LY294002下调了BCRP表达，因此表明Akt途径参与了BCRP表达的调节，但不参与其在这些肺癌细胞系中的定位。最后，选择性BCRP转运抑制剂Ko143并未增加厄洛替尼敏感性，但确实降低了A549和H1650细胞中BCRP的转运活性，因为它诱导了其转运底物拓扑替康的积累。总之，我们的结果表明EGFR和Akt途径参与了BCRP表达、转运和药物转运活性的调节。这些发现为未来研究这些途径的药理调节以提高厄洛替尼与BCRP转运底物药物的抗癌联合疗效提供了依据。
