Differential overexpression of three mdr gene family members in multidrug-resistant J774.2 mouse cells. Evidence that distinct P-glycoprotein precursors are encoded by unique mdr genes

S. I.H. Hsu, L. Lothstein, S. B. Horwitz

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184 Scopus citations


A hallmark of the multidrug-resistant phenotype is the overproduction of a family of 130-180-kDa integral membrane phosphoglycoproteins collectively called P-glycoprotein. Gene-specific hybridization probes were derived from three classes of mouse P-glycoprotein cDNAs. These probes revealed the differential amplification and/or transcriptional activation of three distinct but closely related mdr genes (mdr1a, mdr1b, and mdr2) in independently selected multidrug-resistant J774.2 mouse cell lines. Overexpression of mdr1a and mdr1b was found to correlate, in general, with the differential overproduction of either a 120- or 125-kDa P-glycoprotein precursor, respectively. This same correlation was observed in a single cell line during the course of stepwise selection for resistance to vinblastine in which a switch in gene expression from mdr1b to mdr1a resulted in a switch from the 125- to 120-kDa P-glycoprotein precursor. These findings suggest that differential overexpression of distinct mdr genes which encode unique P-glycoprotein isoforms is a possible mechanism for generating diversity in the multidrug-resistant phenotype.

Original languageEnglish (US)
Pages (from-to)12053-12062
Number of pages10
JournalJournal of Biological Chemistry
Issue number20
Publication statusPublished - Jan 1 1989


ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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