Co-expression of several molecular mechanisms of multidrug resistance and their significance for paclitaxel cytotoxicity in human AML HL-60 cells

Leukemia. 1997 Feb;11(2):253-7. doi: 10.1038/sj.leu.2400557.


Overexpression of P-glycoprotein (PGP), MRP or LRP has been characterized as the 'proximal', while overexpression of the anti-apoptosis Bcl-2 or Bcl-xL relative to the pro-apoptosis Bax protein has been recognized as the 'distal' mechanism of multidrug resistance in human AML cells. In the present studies, we examined whether these mechanisms can co-exist in human AML HL-60 cells. We also determined how these mechanisms would affect the accumulation and cytotoxicity of a PGP substrate, such as Taxol (paclitaxel). For this, immunoblot analyses were performed to determine the expression of PGP, MRP, Myc, Bcl-2, Bcl-xL and Bax on either the multidrug-resistant HL-60 sublines created under the selection pressure of doxorubicin (HL-60/AR), paclitaxel (HL-60/TAX1000) or vincristine (HL-60/VCR), or sublines created by transfection and overexpression of the bcl-2 (HL-60/Bcl-2) or bcl-xL gene (HL-60/Bcl-xL). As compared to the control HL-60, HL-60/AR cells possess high MRP while HL-60/TAX1000 and HL-60/VCR cells express high levels of the mdr-1 encoded PGP. In addition, these multidrug-resistant cells possess 1.5- to 2.5-fold higher Bcl-2, while their Bax and Myc levels are similar to those in the control HL-60 cells. HL-60/TAX1000 and HL-60/VCR cells also express three- and 2.5-fold higher Bcl-xL levels. PGP, but not MRP, overexpression significantly impaired paclitaxel accumulation and paclitaxel-induced apoptosis, as well as reduced its cytotoxic effects as determined by the MTT assay. In contrast, enforced and much higher expression of Bcl-2 in HL-60/Bcl-2 (five-fold) or Bcl-xL in HL-60/Bcl-xL cells (10-fold) significantly reduced paclitaxel-induced apoptosis and the loss of cell viability, without affecting its intracellular accumulation. These results confirm the possibility of co-expression of multiple mechanisms of multidrug resistance in human leukemic cells which had been selected by exposure to a single drug. The results also indicate that MRP overexpression does not confer resistance against paclitaxel. In addition, these findings suggest that, for Bcl-2 and Bcl-xL, enforced overexpression to high levels is necessary to induce paclitaxel resistance in HL-60 cells.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • ATP Binding Cassette Transporter, Subfamily B, Member 1 / biosynthesis
  • ATP Binding Cassette Transporter, Subfamily B, Member 1 / genetics
  • ATP-Binding Cassette Transporters / biosynthesis
  • ATP-Binding Cassette Transporters / genetics
  • Apoptosis / drug effects
  • DNA Fragmentation
  • Doxorubicin / pharmacology
  • Drug Resistance, Multiple / genetics*
  • Drug Resistance, Neoplasm / genetics*
  • Gene Expression Regulation, Leukemic* / drug effects
  • Genes, myc
  • Genes, p53
  • HL-60 Cells / drug effects*
  • HL-60 Cells / metabolism
  • Humans
  • Multidrug Resistance-Associated Proteins
  • Neoplasm Proteins / biosynthesis*
  • Neoplasm Proteins / genetics
  • Paclitaxel / pharmacology*
  • Proto-Oncogene Proteins / biosynthesis
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins c-bcl-2 / biosynthesis
  • Proto-Oncogene Proteins c-bcl-2 / genetics
  • Proto-Oncogene Proteins c-myc / biosynthesis
  • Recombinant Fusion Proteins / biosynthesis
  • Recombinant Fusion Proteins / genetics
  • Transfection
  • Tumor Suppressor Protein p53 / biosynthesis
  • Vincristine / pharmacology
  • bcl-2-Associated X Protein
  • bcl-X Protein


  • ATP Binding Cassette Transporter, Subfamily B, Member 1
  • ATP-Binding Cassette Transporters
  • BAX protein, human
  • BCL2L1 protein, human
  • Multidrug Resistance-Associated Proteins
  • Neoplasm Proteins
  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • Proto-Oncogene Proteins c-myc
  • Recombinant Fusion Proteins
  • Tumor Suppressor Protein p53
  • bcl-2-Associated X Protein
  • bcl-X Protein
  • Vincristine
  • Doxorubicin
  • Paclitaxel