journal contribution
posted on 2023-04-03, 14:26 authored by Jessian L. Munoz, Vivian Rodriguez-Cruz, Steven J. Greco, Vipul Nagula, Kathleen W. Scotto, Pranela Rameshwar <p>Figure S1. The band densities for the western blot for P-gp in Fig. 1D were normalized to β-actin. The data are presented as fold expression for both cell lines, three different experiments. Figure S2. The band densities for cJun/Fos and p-cJun/Fos in the western blots with U87 extracts in Fig. 4B were normalized to β-actin and then presented as Fold Expression, three different experiments. Figure S3. The band densities for cJun/Fos and p-cJun/Fos in the western blots with T98G extracts in Fig. 4B were normalized to β-actin and then presented as Fold Expression, three different experiments. Figure S4. Bands shown for the western blots for P-gp in Fig. 5C were normalized band with the bands for β-actin. The results are expressed as fold expression, three different experiments.</p>
History
ARTICLE ABSTRACT
Glioblastoma multiforme (GBM) commonly resists the frontline chemotherapy treatment temozolomide. The multidrug resistance gene (MDR1) and its protein, P-glycoprotein (P-gp), are associated with chemoresistance. This study investigated the mechanisms underlying MDR1-mediated resistance by GBM to temozolomide. P-gp trafficking was studied by flow cytometry and Western blot analysis. MDR1 expression was analyzed by real-time PCR and reporter gene assays. AP-1 interaction with MDR1 was studied by chromatin immunoprecipitation assay. EGF production was analyzed by ELISA, EGFR signaling was determined by Western blot analysis, and in vivo response to erlotinib and/or temozolomide was studied in nude mice. During the early phase of temozolomide treatment, intracellular P-gp was trafficked to the cell membrane, followed by conformational change into active P-gp. At the later phase, gene transcription of MDR1 was induced by temozolomide-mediated production of EGF. EGF activated ERK1/2-JNK-AP-1 cofactors (c-jun and c-fos). An inhibitor of EGFR kinase (erlotinib) given to nude mice with GBM prevented temozolomide-induced resistance. The results identified an essential role for activated EGFR in the resistance of GBM to temozolomide. Temozolomide resistance occurred through a biphasic response; first, by a conformational change in P-gp into the active form and, second, by releasing EGF, which caused autocrine stimulation of GBM cells to induce MDR1. Pharmacologic inhibition of EGFR kinase blunted the ability of GBM cells to resist temozolomide. These findings may explain reports on the common occurrence of mutant EGFR (EGFRvIII) and EGFR expansion in the resistance of GBM cells. Mol Cancer Ther; 13(10); 2399–411. ©2014 AACR.
