title: G-quadruplex structures formed at the HOX11 breakpoint region contribute to its fragility during t(10;14) translocation in T-cell leukemia.
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.
authors.affiliation: Department of Biochemistry, Indian Institute of Science, Bangalore, India.
authors.forename: Mridula
authors.initials: M
authors.lastname: Nambiar
authors.forename: Mrinal
authors.initials: M
authors.lastname: Srivastava
authors.forename: Vidya
authors.initials: V
authors.lastname: Gopalakrishnan
authors.forename: Sritha K
authors.initials: SK
authors.lastname: Sankaran
authors.forename: Sathees C
authors.initials: SC
authors.lastname: Raghavan
mesh_terms: D001483:Base Sequence; D056905:Chromosome Breakpoints; D043283:Chromosome Fragile Sites; D002873:Chromosome Fragility; D002879:Chromosomes, Human, Pair 10; D002883:Chromosomes, Human, Pair 14; D004261:DNA Replication; D004277:DNA, Single-Stranded; D054856:G-Quadruplexes; D020862:GC Rich Sequence; D015870:Gene Expression; D049452:Green Fluorescent Proteins / Q000096:biosynthesis / Q000235:genetics; D018398:Homeodomain Proteins / Q000235:genetics*; D006801:Humans; D020014:K562 Cells; D008969:Molecular Sequence Data; D054218:Precursor T-Cell Lymphoblastic Leukemia-Lymphoma / Q000235:genetics*; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D014178:Translocation, Genetic
chemical_list: D004277:DNA, Single-Stranded; D018398:Homeodomain Proteins; D011518:Proto-Oncogene Proteins; C485184:enhanced green fluorescent protein; C071250:TLX1 protein, human; D049452:Green Fluorescent Proteins