title: Quantitative determination of MDR1 mRNA expression in peripheral blood lymphocytes: a possible role of genetic polymorphisms in the MDR1 gene.
abstract: BACKGROUND
  P-glycoprotein is a transmembrane efflux pump that extrudes a wide variety of drugs, thereby reducing their intracellular access. In humans, P-glycoprotein is encoded by the MDR1 gene. Recently, several single nucleotide polymorphisms in the MDR1 gene were identified. Moreover, it was postulated that, in addition to the full-length P-glycoprotein, a 'mini' P-glycoprotein was also present in lymphocytes.
  
  
  METHODS
  We investigated the effect of the genetic polymorphisms G2677T and C3435T in the MDR1 gene on MDR1 mRNA expression in FACS-sorted peripheral blood CD4+, CD8+, CD19+, and CD56+ cells. MDR1 mRNA expression was determined in 45 healthy individuals using a real-time quantitative RT-PCR.
  
  
  RESULTS
  We detected the highest expression of MDR1 mRNA in CD56+ cells, followed by CD8+ > CD4+ > CD19+ cells. However, genetic polymorphisms of the MDR1 gene failed to affect (P > 0.05) MDR1 mRNA levels in the peripheral blood lymphocytes. Furthermore, the transcript levels for the MDR1 N-terminal half were almost two-fold lower than that of the MDR1 C-terminal half in all cell populations investigated (P < 0.0001).
  
  
  CONCLUSIONS
  An almost two-fold difference in MDR1 C- and N-terminal half expressions supports the presence of mini-P-glycoprotein, an alternatively spliced form of the full-length molecule, in peripheral blood lymphocytes.
authors.affiliation: Institute of Clinical Pharmacology, University Medical Centre Charité, Humboldt University, Berlin, Germany.kersti.oselin@gmx.net
authors.forename: K
authors.initials: K
authors.lastname: Oselin
authors.forename: I
authors.initials: I
authors.lastname: Nowakowski-Gashaw
authors.forename: P M
authors.initials: PM
authors.lastname: Mrozikiewicz
authors.forename: D
authors.initials: D
authors.lastname: Wolbergs
authors.forename: R
authors.initials: R
authors.lastname: Pähkla
authors.forename: I
authors.initials: I
authors.lastname: Roots
mesh_terms: D015703:Antigens, CD / Q000378:metabolism*; D015704:CD4 Antigens / Q000378:metabolism; D019002:CD56 Antigen / Q000378:metabolism; D016827:CD8 Antigens / Q000378:metabolism; D004247:DNA / Q000302:isolation & purification; D005434:Flow Cytometry / Q000379:methods; D005784:Gene Amplification; D015870:Gene Expression; D019450:Genes, MDR; D005838:Genotype; D006801:Humans; D008214:Lymphocytes / Q000378:metabolism*; D011110:Polymorphism, Genetic; D012333:RNA, Messenger / Q000302:isolation & purification / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods
chemical_list: D015703:Antigens, CD; D015704:CD4 Antigens; D019002:CD56 Antigen; D016827:CD8 Antigens; D012333:RNA, Messenger; D004247:DNA