Structure and expression of the human MDR (P-glycoprotein) gene family

The human MDR (P-glycoprotein) gene family is known to include two members, MDR1 and MDR2. The product of the MDR1 gene, which is responsible for resistance to different cytotoxic drugs (multidrug resistance), appears to serve as an energy-dependent efflux pump for various lipophilic compounds. The function of the MDR2 gene remains unknown. We have examined the structure of the human MDR gene family by Southern hybridization of DNA from different multidrug-resistant cell lines with subfragments of MDR1 cDNA and by cloning and sequencing of genomic fragments. We have found no evidence for any other cross-hybridizing MDR genes. The sequence of two exons of the MDR2 gene was determined from genomic clones. Hybridization with single-exon probes showed that the human MDR1 gene is closely related to two genes in mouse and hamster DNA, whereas MDR2 corresponds to one rodent gene. The human MDR locus was mapped by field-inversion gel electrophoresis, and both MDR genes were found to be linked within 330 kilobases. The expression patterns of the human MDR genes were examined by enzymatic amplification of cDNA. In multidrug-resistant cell lines, increased expression of MDR1 mRNA was paralleled by a smaller increase in the levels of MDR2 mRNA. In normal human tissues, MDR2 was coexpressed with MDR1 in the liver, kidney, adrenal gland, and spleen. MDR1 expression was also detected in colon, lung, stomach, esophagus, muscle, breast, and bladder.

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Physical mapping, amplification, and overexpression of the mouse mdr gene family in multidrug-resistant cells.

Molecular and Cellular Biology ◽

10.1128/mcb.10.4.1642 ◽

1990 ◽

Vol 10 (4) ◽

pp. 1642-1651 ◽

Cited By ~ 95

Author(s):

M Raymond ◽

E Rose ◽

D E Housman ◽

P Gros

Keyword(s):

Molecular Weight ◽

Multidrug Resistance ◽

Gene Family ◽

Cell Lines ◽

Gene Amplification ◽

Genomic Dna ◽

Multidrug Resistant ◽

Pulse Field ◽

P Glycoprotein ◽

Mdr Genes

The mouse mdr gene family consists of three distinct genes (mdr1, mdr2, and mdr3), for which we have isolated full-length cDNA clones. cDNA subfragments corresponding to discrete regions showing little sequence conservation among the three mdr genes were used as gene-specific DNA probes in hybridization experiments. Long-range mapping by pulse-field gel electrophoresis indicated that the three mdr genes are closely linked on a genomic DNA segment of approximately 625 kilobases. The gene order and direction of transcription of the three genes were determined and indicate the arrangement (5') mdr3 (3')-(5') mdr1 (3')-(3') mdr2 (5'). Southern blotting analyses of genomic DNA from a panel of independently derived multidrug-resistant cell lines identified mdr gene amplification in 10 of 12 cell lines studied. In individual cell lines showing gene amplification, the copy number of each of the three mdr genes was identical, suggesting that the three mdr genes became amplified as part of a single amplicon in these cells. Although increased expression of all three mdr genes was detected in 2 of 12 cell lines tested, multidrug resistance was associated in 10 of 12 lines with the independent overexpression of either mdr1 (7 of 12) or mdr3 (3 of 12) but not mdr2. mdr1 overexpression was consistently associated with gene amplification, while increased mdr3 expression was detected in certain cell lines that did not show gene amplification. Increased levels of mdr1 mRNA were linked to the overexpression of a P glycoprotein of apparent molecular weight 180,000 to 200,000, whereas increased mdr3 expression resulted in increased expression of a P glycoprotein of molecular weight 160,000 to 180,000. Our results suggest that at least two members of the mouse mdr gene family, mdr1 and mdr3, can independently confer multidrug resistance in the cell lines examined.

Download Full-text

Physical mapping, amplification, and overexpression of the mouse mdr gene family in multidrug-resistant cells

Molecular and Cellular Biology ◽

10.1128/mcb.10.4.1642-1651.1990 ◽

1990 ◽

Vol 10 (4) ◽

pp. 1642-1651

Author(s):

M Raymond ◽

E Rose ◽

D E Housman ◽

P Gros

Keyword(s):

Molecular Weight ◽

Multidrug Resistance ◽

Gene Family ◽

Cell Lines ◽

Gene Amplification ◽

Genomic Dna ◽

Multidrug Resistant ◽

Pulse Field ◽

P Glycoprotein ◽

Mdr Genes

The mouse mdr gene family consists of three distinct genes (mdr1, mdr2, and mdr3), for which we have isolated full-length cDNA clones. cDNA subfragments corresponding to discrete regions showing little sequence conservation among the three mdr genes were used as gene-specific DNA probes in hybridization experiments. Long-range mapping by pulse-field gel electrophoresis indicated that the three mdr genes are closely linked on a genomic DNA segment of approximately 625 kilobases. The gene order and direction of transcription of the three genes were determined and indicate the arrangement (5') mdr3 (3')-(5') mdr1 (3')-(3') mdr2 (5'). Southern blotting analyses of genomic DNA from a panel of independently derived multidrug-resistant cell lines identified mdr gene amplification in 10 of 12 cell lines studied. In individual cell lines showing gene amplification, the copy number of each of the three mdr genes was identical, suggesting that the three mdr genes became amplified as part of a single amplicon in these cells. Although increased expression of all three mdr genes was detected in 2 of 12 cell lines tested, multidrug resistance was associated in 10 of 12 lines with the independent overexpression of either mdr1 (7 of 12) or mdr3 (3 of 12) but not mdr2. mdr1 overexpression was consistently associated with gene amplification, while increased mdr3 expression was detected in certain cell lines that did not show gene amplification. Increased levels of mdr1 mRNA were linked to the overexpression of a P glycoprotein of apparent molecular weight 180,000 to 200,000, whereas increased mdr3 expression resulted in increased expression of a P glycoprotein of molecular weight 160,000 to 180,000. Our results suggest that at least two members of the mouse mdr gene family, mdr1 and mdr3, can independently confer multidrug resistance in the cell lines examined.

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