Gene: MDR1 maps to 7q21, amplified in several multidrug resistant cell lines. Mitogen activation of the promoter, mediated through the Raf-1 kinase, has been demonstrated, suggesting a role of signal transduction, apoptosis or cell-cycle components in the drug-resistant phenotype (Cornwell M.M. and Smith D.E., 1993).
mRNA: size: 4.5 kb
Protein: 170-kD membrane glycoprotein, member of the
ATP-binding cassette (ABC) superfamily of transporters. P-glycoprotein is highly expressed in secretory organs and tissues, such as the adrenal glands, kidneys, liver, and luminal epithelium of the colon, and it has been postulated that the molecule is involved in steroid transport and protection against xenobiotics (detoxification). Inhibited by verapamil.
The ATP-binding cassette (ABC) superfamily includes genes whose products are transmembrane proteins involved in energy-dependent transport of a wide spectrum of substrates across membranes. Many disease-causing members of this superfamily result in defects in the transport of specific substrates. In eukaryotes, ABC genes typically encode 4 domains that include 2 conserved ATP-binding domains and 2 domains with multiple transmembrane segments. The ATP-binding domains of the ABC genes contain motifs of characteristic conserved residues (Walker A and B motifs) spaced by 90 to 120 amino acids. Both this conserved spacing and the 'signature' or 'C' motif just upstream of the Walker B site distinguish members of the ABC superfamily from other ATP-binding proteins. These features allowed the isolation of new ABC genes by hybridization, degenerate PCR, and inspection of DNA sequence databases (Allikmets R. et al., 1996).
Cell lines:
Tumors:
- Detectable levels of MDR1 mRNA was observed in 25 out of 49 breast tumours, with up to a 100-fold range in expression. A narrower range of
GST-pi expression was also observed in these tumours (Keith W.N. et al., 1990).
- The degree of Pgp expression strongly correlated with the degree of drug resistance in a series of breast cancer specimens (Mechetner E. et al., 1998).
- Expression of both
MRP-1 and MDR1 genes was observed by RT-PCR in a series of tumor (n = 74) and normal adjacent (n = 55) breast tissue samples. The expression of MDR1, however, was low, with the level of expression being 25 times less than the drug-resistant control cell line KB 8-5. Immunohistochemical analysis of P-glycoprotein corroborated the PCR results. MDR1 expression was independent of grade, stage, tumor size, nodal status, metastasis, and
estrogen receptor and
progesterone receptor status. There was, however, a significant correlation of MDR1 expression with age and histology. Approximately twice the expression of MDR1 was observed in the < 50 age group compared to the > 50 age group, and lobular carcinoma had 4 times the expression of MDR1 of other histological types (Dexter D.W. et al., 1998).
- MDR1 mRNA was detected in 40% of breast cancers samples tested by RT-PCR with 40 cycles of PCR amplification. When reducing the PCR amplification cycles to 28, the MDR1 gene expression signal disappeared from breast cancers of the highest expressers; however, known MDR1 positive control normal tissues, such as adrenal, kidney, and liver continued to show an expression product. Western and Northern blots failed to demonstrate the MDR1 gene product, P-glycoprotein, in these breast cancers. In contrast, physiologic levels of P-glycoprotein was clearly detected in normal adrenal, kidney, and liver by these techniques. Immunohistochemistry confirmed that breast carcinoma cells lacked P-glycoprotein expression; however, interstitial mononuclear cells, morphologically consistent with lymphocytes or macrophages did show immunostaining in some of these breast tumors (Yang X. et al., 1999).
- The long-term prognostic value of tumoural MDR1 and
MRP-1, along with p53 and other classical parameters, was analysed on 85 node-positive breast cancer patients receiving anthracycline-based adjuvant therapy. All patients underwent tumour resection plus irradiation and adjuvant chemotherapy (the majority receiving fluorouracil-epirubicin-cyclophosphamide). Median follow-up for the 54 alive patients was 7.8 years. Mean age was 53.7 years (range 28-79) and 54 patients were post-menopausal. MDR1 and
MRP-1 expression were quantified according to an original reverse transcription polymerase chain reaction multiplex assay with colourimetric enzyme-linked immunosorbent assay detection (beta2-microglobulin as control). P53 protein was analysed using an immunoluminometric assay. MDR1 expression varied within an 11-fold range (mean 94, median 83),
MRP-1 within a 45-fold range (mean 315, median 242) and p53 protein from the limit of detection (0.002 ng mg
-1) up to 35.71 ng mg
-1 (mean 1.18, median 0.13 ng mg
-1). P53 protein was significantly higher in
oestrogen receptor (ER)-negative than in
ER-positive tumours. The higher the p53, the lower the MDR1 expression. P53 was not linked to
progesterone receptor (PgR) status, S phase fraction, or
MRP-1. Significantly greater MDR1 expression was observed in grade I tumours. No relationship was observed between MDR1 and
MRP-1. Neither MDR1 nor
MRP-1 was linked to
ER or
PgR status. Unlike MDR1,
MRP-1 was correlated with the S phase: the greater the
MRP-1, the lower the S phase. Univariate Cox analyses revealed that MDR1,
MRP-1, p53 and S phase had no significant influence on progression-free or specific survival (Ferrero J.M. et al., 2000).
Allikmets R. et al. (1996) Characterization of the human ABC superfamily: isolation and mapping of 21 new genes using the expressed sequence tags database. Hum. Molec. Genet. 5, 1649-1655.
Chauffert B. et al. (1999) Actualités sur les mécanismes de la chimiorésistance. Bull. Cancer 86, 97-103
Cornwell M.M. and Smith D.E. (1993) A signal transduction pathway for activation of the mdr1 promotor involves the proto-oncogene c-raf kinase. J. Biol. Chem. 268, 15347-15350.
Dexter D.W. et al. (1998) Quantitative reverse transcriptase-polymerase chain reaction measured expression of MDR1 and MRP in primary breast carcinoma. Clin. Cancer Res. 4, 1533-1542.
Ferrero J.M. et al. (2000) Application of an original RT-PCR-ELISA multiplex assay for MDR1 and
MRP-1, along with p53 determination in node-positive breast cancer patients. Br. J. Cancer 82, 171-177.
Keith W.N. et al. (1990) Expression of mdr1 and
gst-pi in human breast tumours: comparison to in vitro chemosensitivity. Br. J. Cancer 61, 712-716.
Mechetner E. et al. (1998) Levels of multidrug resistance (MDR1) P-glycoprotein expression by human breast cancer correlate with in vitro resistance to taxol and doxorubicin. Clin. Cancer Res. 4, 389-398.
Ogretmen B. and Safa A.R. (1999) Negative regulation of MDR1 promoter activity in MCF-7, but not in multidrug resistant MCF-7/Adr, cells by cross-coupled NF-kappaB/p65 and c-Fos transcription factors and their interaction with the CAAT region. Biochemistry 38, 2189-2199.
Roninson I.B. et al. (1986) Isolation of human mdr sequences amplified in multidrug-resistant KB carcinoma cells. Proc. Natl. Acad. Sci. USA 83, 4538-4542.
Yang X. et al. (1999) MDR1 gene expression in primary and advanced breast cancer. Lab. Invest. 79, 271-280.
