A homologue of the mammalian multidrug resistance gene (mdr) is functionally expressed in the intestine of Xenopus laevis

Gonzalo Castillo, Heng Jia Shen, Susan Band Horwitz

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


P-glycoprotein is an integral membrane protein that functions in multidrug resistance (MDR) cells as a drug efflux pump to maintain intracellular concentrations of antitumor drugs below cytotoxic levels. A homologue of the mammalian mdr gene has been isolated and characterized from Xenopus laevis (Xe-mdr). The cDNA was isolated from a tadpole cDNA library using the full length mouse mdr1b cDNA as a probe. The Xe-mdr encodes a protein that is 66% identical to the mouse mdr1b and 68% identical to the human mdr1. The predicted structure of the Xe-mdr gene product identifies twelve membrane spanning domains and two ATP binding sites both of which are the hallmark of the ABC (ATP binding cassette) transporters. Xe-mdr mRNA is expressed as a single message of 4.5 kb and is found predominantly in the intestine. Xe-mdr message is increased 3- to 4-fold in the ileum compared to the rest of the small intestine. In situ hybridization of sequential sections from the small intestine localized the expression of the Xe-mdr to the cells lining the lumenal epithelium. Brush border membrane vesicles prepared from the small intestine of Xenopus laevis effluxed vinblastine in an ATP-dependent manner. Efflux was decreased by verapamil, a known inhibitor of P-glycoprotein function. These studies indicate that the structure of Xe-mdr has been conserved and suggest that the protein has a role in maintaining the function of the normal intestine in Xenopus.

Original languageEnglish (US)
Pages (from-to)113-123
Number of pages11
JournalBBA - Gene Structure and Expression
Issue number2-3
StatePublished - Jun 9 1995
Externally publishedYes


  • Multidrug resistance
  • P-glycoprotein
  • Transport
  • X. laevis

ASJC Scopus subject areas

  • Structural Biology
  • Biophysics
  • Biochemistry
  • Genetics


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