Mitochondrial localization of P-glycoprotein in the human breast cancer cell line MCF-7/ADM and its functional characterization
ABSTRACT The current view of multidrug resisitance is that overexpression of membrane P-glycoprotein (P-gp) is a major causative factor. However, the controversial presence of subcellular P-gp may also participate in the drug resistance. In this study, we sought to investigate the localization and functional characterization of P-gp in mitochondria isolated from MCF-7 and doxorubicin-resistant MCF-7 (MCF-7/ADM) cells. Mitochondria were isolated and purified from the MCF-7 cell line and its resistant cells MCF-7/ADM. We used electron microscopy, western blot analysis and confocal microscopy to demonstrate the localization of P-gp in the mitochondria of MCF-7/ADM cells. Flow cytometry was used to evaluated the efflux function of mitochondrial P-gp in the presence or absence of the P-gp inhibitor cyclosporine A (CsA). Mitochondria were isolated and purified successfully and were analyzed by electron microscopy. Western blotting demonstrated the expression of P-gp in the cell membrane and purified mitochondria from MCF-7/ADM cells but not from sensitive MCF-7 cells. Immunofluorescence analysis using confocal microscopy demonstrated the localization of P-gp [labeled with green fluorescence (FITC)] to the mitochondria [labeled with red fluorescence (Mitotracker Deep red 633)] of MCF-7/ADM cells and that was absent in MCF-7 cells. Rho123 (a mitochondrial fluorescent probe) accumulation was largely reduced and efflux was strongly increased in the mitochondria of MCF-7/ADM cells compared to those of MCF-7 cells (P<0.01), and these were completely reversed in the presence of the P-gp inhibitor CsA (P<0.01). No significant changes were observed in the mitochondria of MCF-7 cells (P>0.05). P-gp is expressed in the mitochondria of doxorubicin-resistant MCF-7 cells and has an efflux function. It could be involved in multidrug resistance at the subcellular site by pumping out anticancer drugs from mitochondria to protect the function of mitochondria.
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ABSTRACT: P-glycoprotein (P-gp), traditionally linked to cancer poor prognosis and multidrug resistance, is undetectable in normal gastric mucosa and overexpressed in gastric cancer (GC). We propose that P-gp may be involved in Helicobacter pylori (Hp)-related gastric carcinogenesis by inhibiting apoptosis. Aim of the study was to evaluate the expression of P-gp in fetal stomach and in Hp-related gastric carcinogenesis, the epigenetic control of the multi-drug resistance-1 (MDR1) gene, the localization and interaction between P-gp and Bcl-x(L) and the effect of the selective silencing of P-gp on cell survival. P-gp and Bcl-xl expression was evaluated by immunohistochemistry on 28 spontaneously abortive human fetuses, 66 Hp-negative subjects, 138 Hp-positive chronic gastritis (CG) of whom 28 with intestinal metaplasia (IM) and 45 intestinal type GCs. P-gp/Bcl-x(L) colocalization was investigated by confocal immunofluorescence microscopy and protein-protein interaction by co-immunoprecipitation, in basal conditions and after stress-induced apoptosis, in GC cell lines AGS and MKN-28 and hepatocellular carcinoma cell line Hep-G2. The role of P-gp in controlling apoptosis was evaluated by knocking down its expression with a specific small interfering RNAs in stressed AGS and MKN-28 cell lines. P-gp is expressed in the gastric mucosa of all human fetuses while, it is undetectable in adult normal mucosa and re-expressed in 30/110 Hp-positive non-IM-CG, 28/28 IM-CG and 40/45 GCs. P-gp expression directly correlates with that of Bcl-x(L) and with the promoter hypomethylation of the MDR1 gene. In GC cell lines, P-gp is localized on the plasma membrane and mitochondria where it colocalizes with Bcl-x(L). Co-immunoprecipitation confirms the physical interaction between P-gp and Bcl-x(L) in AGS, MKN-28 and Hep-G2, at both basal level and after stress-induced apoptosis. The selective silencing of P-gp sensitizes GC cells to stress-induced apoptosis. P-gp behaves as an oncofetal protein that, by cross-talking with Bcl-x(L), acts as an anti-apoptotic agent in Hp-related gastric carcinogenesis.Laboratory Investigation 07/2012; 92(10):1407-18. DOI:10.1038/labinvest.2012.100 · 3.83 Impact Factor
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ABSTRACT: Oxidative stress contributes to tissue injury and cell death during the development of various diseases. The present study aims at investigating whether oxidative stress triggered by the exposure to hydrogen peroxide (H(2)O(2)) can induce apoptosis of induced pluripotent stem cells (iPS cells) in a mechanism mediated by insulin-like growth factor (IGF-1) and microRNA-1 (miR-1). iPS cells treated with H(2)O(2) showed increases in miR-1 expression, mitochondria dysfunction, cytochrome-c release and apoptosis, Addition of IGF-1 into the iPS cell cultures reduced the H(2)O(2) cytotoxicity. Prediction algorithms showed that 3'-untranslated regions of IGF-1 gene as a target of miR-1. Moreover, miR-1 mimic, but not miR-1 mimic negative control, diminished the protective effect of IGF-1 on H(2)O(2)-induced mitochondrial dysfunction, cytochrome-c release and apoptosis in iPS cells. In conclusion, IGF-1 inhibits H(2)O(2)-induced mitochondrial dysfunction, cytochrome-c release and apoptosis. IGF-1's effect is, at least partially, regulated by miR-1 in iPS cells.Biochemical and Biophysical Research Communications 09/2012; 426(4):615-9. DOI:10.1016/j.bbrc.2012.08.139 · 2.28 Impact Factor
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ABSTRACT: This study was designed to investigate functional localization of both efflux (P-glycoprotein, P-gp) and influx (peptide) transporters in the mitochondrial membrane of cultured rabbit primary corneal epithelial cells (rPCECs). Isolation and purification of mitochondria was performed by optimized cell fractionation method. Mitochondrial integrity was measured by JC-1 uptake experiment. The efflux activity of P-gp was assessed by performing in vitro uptake studies on isolated mitochondria with Rhodamine 123 (Rho-123) alone and in the presence of P-gp inhibitors (quinidine and cyclosporine A) using fluorimetry and flow cytometry analysis. Functional activity of peptide transporter was assessed by performing in vitro uptake studies of [3H] Gly-sar on isolated mitochondria in the presence or absence of peptide transporter substrate (Val-Val). Molecular characterization of P-gp and peptide transporter was assessed by western blot and confocal analysis. Enhanced JC-1 accumulation in the isolated fraction confirmed mitochondrial membrane integrity. Significantly higher uptake of Rho-123 on isolated mitochondria was observed in the presence of quinidine (75 and 100 μM) and cyclosporine A (10μM). Significantly lower uptake of [3H] Gly-sar was observed in the presence of val-val due to competitive inhibition of peptide transporter on isolated mitochondria. Western blot and confocal analysis further confirmed the presence of P-gp and peptide transporter on the mitochondrial membrane of rPCECs. The present study demonstrates the functional and molecular characterization of P-gp and peptide transporters in the mitochondrial membranes of rPCECs. This knowledge of mitochondrial existence of P-gp and peptide transporter will aid in the development of subcellular ocular drug delivery strategies.Experimental Eye Research 10/2012; 106. DOI:10.1016/j.exer.2012.10.006 · 3.02 Impact Factor