       Document 0752
 DOCN  M9640752
 TI    Development of zidovudine (AZT) resistance in Jurkat T cells is
       associated with decreased expression of the thymidine kinase (TK) gene
       and hypermethylation of the 5' end of human TK gene.
 DT    9604
 AU    Wu S; Liu X; Solorzano MM; Kwock R; Avramis VI; Department of
       Pediatrics, USC School of Medicine, Childrens; Hospital Los Angeles
       90027, USA.
 SO    J Acquir Immune Defic Syndr Hum Retrovirol. 1995 Jan 1;8(1):1-9. Unique
       Identifier : AIDSLINE GENBANK/X54729
 AB    The T-cell line Jurkat E6-1 was rendered resistant to zidovudine (AZT)
       in vitro by exposure to low but gradually increased concentrations of
       the drug. Biochemical pharmacology studies of [3H]AZT in the
       AZT-resistant T-cell lines showed a significant reduction of AZT
       phosphorylation to the mono-, di-, and triphosphate anabolites.
       Peripheral blood mononuclear cells (PBMCs) from pediatric patients with
       human immunodeficiency virus type 1 (HIV-1) infection showed a similar
       pattern of decreased AZT anabolism. Enzymatic studies with purified
       thymidine kinase (TK) preparations from these cell lines showed a
       gradual decline in Vmax related to their level of resistance to AZT. The
       Jurkat/AZT-20 and Jurkat/AZT-100 cells were studied in greater detail
       with reverse transcriptase/polymerase chain reaction (RT/PCR) cloned
       probes to determine possible molecular mechanisms of resistance to AZT.
       TK mRNA was significantly decreased (approximately 5- to 10-fold) in the
       AZT-resistant T-cell lines. Southern blot analyses indicated that there
       were no major rearrangements or deletions of the TK gene, but the 5' end
       of the gene in the AZT-resistant cells is highly methylated when
       compared to wild-type cells. No apparent differences were seen in
       thymidylate kinase (dTMPk) mRNA levels in the same T-cell lines. Thus
       the decreased expression of TK mRNA and resultant TK enzymatic activity
       is responsible for the observed reduction in the AZT anabolism in the
       resistant T-cell lines. Decreased T-cell TK activity could allow
       wild-type, AZT-sensitive HIV-1 to replicate in the presence of
       subinhibitory AZT triphosphate (AZT-TP) cellular concentrations enabling
       a genetic variant with drug resistance to emerge and outgrow the
       AZT-sensitive, wild-type virus.
 DE    Antiviral Agents/*PHARMACOLOGY  Base Sequence  Blotting, Southern  Cell
       Line  Cells, Cultured  Child  Down-Regulation (Physiology)  Drug
       Resistance  DNA/ANALYSIS/ISOLATION & PURIF  DNA Primers/CHEMISTRY  *Gene
       Expression Regulation, Enzymologic  Human  HIV
       Infections/COMPLICATIONS/DRUG THERAPY  HIV-1  Leukocytes,
       Mononuclear/DRUG EFFECTS/ENZYMOLOGY/VIROLOGY  Methylation  Molecular
       Sequence Data  Phosphorylation  Polymerase Chain Reaction  RNA,
       Messenger/BIOSYNTHESIS  Support, Non-U.S. Gov't  T-Lymphocytes/DRUG
       EFFECTS/*ENZYMOLOGY  Thymidine Kinase/BIOSYNTHESIS/*GENETICS
       Transcription, Genetic  Zidovudine/*PHARMACOLOGY  JOURNAL ARTICLE

       SOURCE: National Library of Medicine.  NOTICE: This material may be
       protected by Copyright Law (Title 17, U.S.Code).

