G-quadruplex Structures Formed at the HOX11 Breakpoint Region Contribute to Its Fragility During t(10;14) Translocation in T-cell Leukemia

Mol Cell Biol. 2013 Nov;33(21):4266-81. doi: 10.1128/MCB.00540-13. Epub 2013 Sep 3.

Abstract

The t(10;14) translocation involving the HOX11 gene is found in several T-cell leukemia patients. Previous efforts to determine the causes of HOX11 fragility were not successful. The role of non-B DNA structures is increasingly becoming an important cause of genomic instability. In the present study, bioinformatics analysis revealed two G-quadruplex-forming motifs at the HOX11 breakpoint cluster. Gel shift assays showed formation of both intra- and intermolecular G-quadruplexes, the latter being more predominant. The structure formation was dependent on four stretches of guanines, as revealed by mutagenesis. Circular dichroism analysis identified parallel conformations for both quadruplexes. The non-B DNA structure could block polymerization during replication on a plasmid, resulting in consistent K(+)-dependent pause sites, which were abolished upon mutation of G-motifs, thereby demonstrating the role of the stretches of guanines even on double-stranded DNA. Extrachromosomal assays showed that the G-quadruplex motifs could block transcription, leading to reduced expression of green fluorescent protein (GFP) within cells. More importantly, sodium bisulfite modification assay showed the single-stranded character at regions I and II of HOX11 in the genome. Thus, our findings suggest the occurrence of G-quadruplex structures at the HOX11 breakpoint region, which could explain its fragility during the t(10;14) translocation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • Chromosome Breakpoints
  • Chromosome Fragile Sites
  • Chromosome Fragility*
  • Chromosomes, Human, Pair 10
  • Chromosomes, Human, Pair 14
  • DNA Replication
  • DNA, Single-Stranded
  • G-Quadruplexes*
  • GC Rich Sequence
  • Gene Expression
  • Green Fluorescent Proteins / biosynthesis
  • Green Fluorescent Proteins / genetics
  • Homeodomain Proteins / genetics*
  • Humans
  • K562 Cells
  • Molecular Sequence Data
  • Precursor T-Cell Lymphoblastic Leukemia-Lymphoma / genetics*
  • Proto-Oncogene Proteins / genetics*
  • Translocation, Genetic*

Substances

  • DNA, Single-Stranded
  • Homeodomain Proteins
  • Proto-Oncogene Proteins
  • enhanced green fluorescent protein
  • TLX1 protein, human
  • Green Fluorescent Proteins