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Expression of the multidrug resistance proteins MRP2 and MRP3 in human hepatocellular carcinoma
A T Nies1, J König, M Pfannschmidt
1Division of Tumor Biochemistry, Deutsches Krebsforschungszentrum, Heidelberg, Germany. a.nies@dkfz.de
Abstract:
Treatment of hepatocellular carcinoma (HCC) by chemotherapy is often impeded by the intrinsic multidrug resistance (MDR) of this frequent primary cancer of the liver. The MDR phenotype can be caused by ATP-dependent export of chemotherapeutic drugs across the plasma membrane being mediated by transporters of the MDR P-glycoprotein family or of the multidrug resistance protein (MRP) family. To elucidate the role of MRP family members in HCC, we analyzed the expression and subcellular localization of MRP1 (ABCC1), MRP2 (ABCC2) and MRP3 (ABCC3); all 3 isoforms have been shown to confer resistance to chemotherapeutic drugs. Semiquantitative RT-PCR demonstrated that MRP2 and MRP3 mRNA expression in HCC was at least 10-fold higher than MRP1 mRNA expression. MRP2 immunostaining was observed in 87% (33/38) of HCC samples. MRP2 was localized in the plasma membrane in a polarized fashion, either in trabecular structures resembling the canalicular membrane or in the luminal membrane when cells had a pseudoglandular arrangement. MRP3 was detected in all samples examined (9/9) by RT-PCR and by immunofluorescence microscopy. MRP3 was localized to the basolateral membrane of carcinoma cells. Double-label immunofluorescence microscopy with antibodies specific for MRP2 or MRP3 indicated that carcinoma cells expressed both MRP isoforms simultaneously. When MRP1 was detected by immunofluorescence microscopy, it was localized on the intracellular membranes of carcinoma cells. Thus, plasma membrane expression of MRP2 and MRP3, but not of MRP1, can contribute to the MDR phenotype of HCC.
Insights
Multidrug resistance (MDR) in liver cancer (HCC) involves transporters like MRP2 and MRP3. These proteins, found on the cell surface, contribute to chemotherapy resistance, unlike MRP1 which is intracellular.
Area of Science:
- Hepatocellular Carcinoma Research
- Cancer Biology
- Molecular Medicine
Background:
- Hepatocellular carcinoma (HCC) frequently exhibits multidrug resistance (MDR), hindering chemotherapy effectiveness.
- MDR in HCC is often mediated by ATP-dependent drug efflux transporters, including the multidrug resistance-associated protein (MRP) family.
- Understanding the role of specific MRP isoforms is crucial for developing strategies to overcome HCC drug resistance.
Purpose of the Study:
- To investigate the expression and subcellular localization of MRP1, MRP2, and MRP3 in hepatocellular carcinoma.
- To determine the contribution of these MRP isoforms to the MDR phenotype in HCC.
- To correlate transporter expression and localization with chemotherapy resistance in liver cancer.
Main Methods:
- Semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) for mRNA expression analysis.
- Immunohistochemistry and immunofluorescence microscopy for protein expression and subcellular localization.
- Double-label immunofluorescence to assess co-expression of MRP isoforms within HCC cells.
Main Results:
- MRP2 and MRP3 mRNA levels were significantly higher (≥10-fold) than MRP1 in HCC.
- MRP2 was detected in 87% of HCC samples, localized to the plasma membrane (canalicular or luminal).
- MRP3 was found in all examined samples, localized to the basolateral membrane; both MRP2 and MRP3 were co-expressed in carcinoma cells. MRP1 was localized intracellularly.
Conclusions:
- Plasma membrane expression of MRP2 and MRP3 in HCC cells contributes to the multidrug resistance phenotype.
- MRP1 does not appear to contribute to MDR in HCC due to its intracellular localization.
- Targeting MRP2 and MRP3 may represent a therapeutic strategy to enhance chemotherapy efficacy in hepatocellular carcinoma.
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