A 190-kilodalton protein overexpressed in non-P-glycoprotein-containing multidrug-resistant cells and its relationship to the MRP gene.
BACKGROUND
A 190k (190-kilodalton) membrane protein has been identified in several multidrug-resistant (MDR) cell lines that show decreased drug accumulation without expression of P-glycoprotein. It is not clear whether this 190k protein is involved directly in drug efflux. Recently, a gene for a putative transporter protein, MRP (multidrug resistance-associated protein) has been sequenced and localized to chromosome 16. The protein encoded by this gene contains a 7-amino-acid sequence present in the synthetic peptide used to generate the antiserum recognizing the 190k protein.


OBJECTIVE
The study was undertaken to clarify the relationship of the 190k protein to MRP gene expression in non-P-glycoprotein-containing MDR cells of the large-cell and adenocarcinoma lung cancer lines, COR-L23 and MOR.


METHODS
Expression of the 190k protein was determined by Western blot analysis and that of the MRP gene by polymerase chain reaction amplification of complementary DNA reverse transcribed from RNA. Abnormalities of chromosome 16 were investigated in chromosome spreads by fluorescence in situ hybridization.


RESULTS
The amount of detectable 190k protein is closely associated with degree of drug resistance. Cell lines surviving in higher drug concentrations have greater amounts of protein, and revertant lines grown without drug for up to 28 weeks show reduced expression of the protein together with enhanced drug sensitivity. The 190k protein appears to be one of the major proteins differentially expressed in membranes of drug-resistant cells. The amount of MRP messenger RNA correlates closely with that of the 190k protein. The MDR cells contain amplified chromosome 16 material with many double minutes in the large-cell lung tumor lines and an enlarged chromosome 16 in the adenocarcinoma lines.


CONCLUSIONS
The 190k protein detected immunologically is likely to be the protein, encoded by the MRP gene, which becomes overexpressed in these cells as a consequence of chromosomal amplification and fragmentation.


CONCLUSIONS
Though associated with drug resistance, enhanced drug efflux, and decreased drug accumulation in cell lines, the role of this protein in clinical resistance has yet to be determined.
Barrand
M A
MA
MRC Clinical Oncology and Radiotherapeutics Unit, MRC Centre, Cambridge, England.
Heppell-Parton
A C
AC
Wright
K A
KA
Rabbitts
P H
PH
Twentyman
P R
PR
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000230:Adenocarcinoma / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D018287:Carcinoma, Large Cell / Q000235:genetics* / Q000378:metabolism; D018288:Carcinoma, Small Cell / Q000235:genetics* / Q000378:metabolism; D002352:Carrier Proteins; D002869:Chromosome Aberrations; D025063:Chromosome Disorders; D002885:Chromosomes, Human, Pair 16; D004351:Drug Resistance / Q000235:genetics* / Q000502:physiology; D015870:Gene Expression; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008175:Lung Neoplasms / Q000235:genetics* / Q000378:metabolism; D008562:Membrane Glycoproteins; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011817:Rabbits; D014407:Tumor Cells, Cultured
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins