Molecular analysis of the T-cell acute lymphoblastic leukemia-associated t(1;7)(p34;q34) that fuses LCK and TCRB.
Previously we had characterized the t(1;7)(p34;q34) translocation from HSB-2. This translocation fused the beta T-cell receptor gene (TCRB) constant region and transcriptional enhancer with the type I transcription unit of the LCK gene on the derivative 1 [der(1)] chromosome. The type II promoter was translocated to the der(7) chromosome. Regarding the mechanism of the t(1;7) in HSB-2, we identified an alternating purine-pyrimidine tract (G-T)17 at the 1p34/LCK breakpoint. Additionally, sequence analysis of both breakpoint junctions provided data that implicate the V(D)J recombinase in formation of the t(1;7). A heptamer-nonamer recognition sequence with a 12-bp spacer was found in the immediate vicinity of the 1p34/LCK breakpoint and, thus, chromosomal breakage at 1p34 may be explained as resulting from recombinase activity. Because phosphorylation of Tyr-505 in vivo regulates the tyrosine kinase activity of p56lck we amplified a region from LCK exon 12 that contains the codon for Tyr-505 and showed no mutation of this codon in HSB-2 DNA and, therefore, p56lck in HSB-2 is not activated by mutation of Tyr-505. We have analyzed LCK gene expression in HSB-2 and SUP-T12 cell lines. RNase protection analysis identified almost exclusively type I transcripts in HSB-2. An independent t(1;7) in SUP-T12 also resulted in the juxtaposition of LCK to TCRB. The breakpoint in SUP-T12 occurred 2 kb 5' of the type II promoter, leaving an intact LCK gene on the der(1) chromosome. RNase protection analysis identified both type I and type II LCK transcripts in a 3:1 ratio in SUP-T12. Factors other than proximity to the TCRB enhancer must affect promoter utilization in this cell line.
Burnett
R C
RC
Department of Medicine, University of Chicago, IL.
Thirman
M J
MJ
Rowley
J D
JD
Diaz
M O
MO
D001483:Base Sequence; D002874:Chromosome Mapping; D002878:Chromosomes, Human, Pair 1; D002897:Chromosomes, Human, Pair 7; D003001:Cloning, Molecular; D003062:Codon; D017931:DNA Primers; D006801:Humans; D007438:Introns; D015459:Leukemia-Lymphoma, Adult T-Cell / Q000235:genetics*; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D011505:Protein-Tyrosine Kinases / Q000235:genetics*; D012326:RNA Splicing; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000235:genetics*; D012091:Repetitive Sequences, Nucleic Acid; D014158:Transcription, Genetic; D014178:Translocation, Genetic
D003062:Codon; D017931:DNA Primers; D016693:Receptors, Antigen, T-Cell, alpha-beta; D011505:Protein-Tyrosine Kinases; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck)