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Inheritance of chromosome 7 is associated with a drug-resistant phenotype in somatic cell hybrids
M de Silva1, P Kantharidis, D M Wall
1Department of Medical Oncology, Austin & Repatriation Medical Centre, Victoria, Australia.
Abstract:
A major form of drug resistance in tumour cells known as classical multidrug resistance (MDR) is associated with the overexpression of the mdr1 gene product, the membrane protein P-glycoprotein (P-gp), which acts as an energy-dependent drug efflux pump. In this study the inheritance of P-gp expression was examined using hybrids formed after somatic cell fusion between a drug-sensitive human T-cell leukaemia cell line, CEM/CCRF, and a drug-resistant derivative, CEM/A7, which is characterized by a clonal chromosomal duplication dup(7)(q11.23q31.2). Fourteen hybrids, chosen at random, were analysed by reverse transcriptase-polymerase chain reaction (RT-PCR) and by binding studies involving the monoclonal antibody MRK16, which recognises an external P-gp epitope. Only two hybrids were positive for both MRK16 antibody labelling and mdr1 mRNA. Partial karyotypic analysis of all hybrids revealed that only the MRK16-positive hybrids contained the duplication in chromosome 7 seen in the CEM/A7 parental MDR line. Therefore, P-gp overexpression in the MRK16-positive hybrids may be linked to the inheritance of chromosome 7 from CEM/A7 and possibly associated with the chromosome 7 abnormality.
Insights
Inheritance of P-glycoprotein (P-gp) expression in multidrug resistance (MDR) was studied. P-gp overexpression in hybrids was linked to chromosome 7 duplication from the drug-resistant parent cell line.
Area of Science:
- Molecular Biology
- Cancer Cell Biology
- Genetics
Background:
- Multidrug resistance (MDR) in tumors is often mediated by P-glycoprotein (P-gp), an efflux pump encoded by the mdr1 gene.
- P-gp overexpression is a significant challenge in cancer chemotherapy, reducing drug efficacy.
- Understanding the genetic basis of P-gp expression is crucial for developing strategies to overcome MDR.
Purpose of the Study:
- To investigate the inheritance pattern of P-glycoprotein (P-gp) expression in somatic cell hybrids.
- To determine the relationship between P-gp expression and specific chromosomal abnormalities.
- To elucidate the genetic linkage of multidrug resistance (MDR) to chromosome 7.
Main Methods:
- Somatic cell fusion of drug-sensitive (CEM/CCRF) and drug-resistant (CEM/A7) human T-cell leukemia lines.
- Analysis of fourteen randomly selected hybrids using reverse transcriptase-polymerase chain reaction (RT-PCR) for mdr1 mRNA detection.
- Assessment of P-gp expression via MRK16 monoclonal antibody binding studies and partial karyotypic analysis.
Main Results:
- Only two out of fourteen hybrids exhibited both P-gp expression (MRK16 binding) and mdr1 mRNA.
- These P-gp-positive hybrids possessed the characteristic dup(7)(q11.23q31.2) chromosomal duplication found in the drug-resistant parent (CEM/A7).
- The drug-sensitive hybrids lacked both P-gp expression and the specific chromosome 7 abnormality.
Conclusions:
- P-glycoprotein (P-gp) overexpression in these somatic cell hybrids is strongly associated with the inheritance of chromosome 7 from the multidrug-resistant (MDR) parent.
- The specific chromosomal abnormality, dup(7)(q11.23q31.2), on chromosome 7 appears to be linked to P-gp overexpression and MDR.
- This suggests a genetic mechanism involving chromosome 7 in the regulation of P-gp expression and drug resistance.