Molecular analysis of the genomic inversion and insertion of AF10 into MLL suggests a single‐step event

Abstract

The interstitial insertion of genetic material from one chromosome into another can achieve the type of gene-gene fusions more usually associated with chromosome translocations. An example of such an interstitial insertion, which has created an MLL-AF10 fusion in an acute myeloid leukaemia, has been analysed at the genomic level. The genomic fusion, which resulted in the juxtaposition of 3' AF10 sequence to 5' MLL sequence, was identified within MLL and AF10 intronic sequences. It was further established that the remaining 3' MLL sequence, from exon 6 onwards, was fused to novel sequence of unknown origin (named FM3 for fused to MLL 3'). The points of fusion of these 5' and 3' portions of MLL matched to adjacent nucleotides and lay between exons 5 and 6. The FM3 sequence was shown to be from chromosome arm 10p and located close to AF10 in a proximal position. It was subsequently demonstrated that in the leukaemia a third fusion existed between 5' AF10 and the FM3 sequence at a point immediately downstream from its fusion to MLL. It was therefore concluded that the MLL-AF10 gene fusion is the result of a simultaneous transposition of genetic material into the MLL gene and the joining of the remaining free ends on chromosome 10. This kind of event, characterised completely here for the first time, is a means to achieve a fusion when the genes involved lie in opposite orientations and results in three genomic junctions.

Cryptic rearrangement involving MLL and AF10 occurring in utero

“…3 Thus, complex chromosomal rearrangements, requiring at least three breaks are required for an in-frame 5 0 MLL-3 0 AF10 fusion to occur. 4 Although these rearrangements are usually visible at the cytogenetic level, as is illustrated by this case, they can occasionally be cryptic underlining the importance of using FISH in addition to G-banding to characterise leukaemia-associated cytogenetic changes.…”

Cryptic rearrangement involving MLL and AF10 occurring in utero

“…3 Thus, complex chromosomal rearrangements, requiring at least three breaks are required for an in-frame 5 0 MLL-3 0 AF10 fusion to occur. 4 Although these rearrangements are usually visible at the cytogenetic level, as is illustrated by this case, they can occasionally be cryptic underlining the importance of using FISH in addition to G-banding to characterise leukaemia-associated cytogenetic changes.…”

Solution structure of the nonmethyl‐CpG‐binding CXXC domain of the leukaemia‐associated MLL histone methyltransferase

“…With the structure of the CXXC domain now available, it will be possible to design nondisruptive mutations that can help to define the role of individual residues in these activities, and thus promoting a deeper understanding of the role of the CXXC domain in transformation by MLL fusion proteins. The CXXC domain is retained in all forms of leukaemogenic MLL fusion proteins, including partial tandem duplications (Lochner et al , 1996) and internal PHD finger 1 deletions (Chaplin et al , 2001; von Bergh et al , 2001; Deveney et al , 2003; Morel et al , 2003). Thus, novel approaches to the treatment of MLL‐associated leukaemias might involve addressing the continued occupancy of key target genes by MLL fusion proteins by disrupting the interaction between the CXXC domain and nonmethyl‐CpG DNA.…”

Identification and molecular characterisation of a CALM-AF10 fusion in acute megakaryoblastic leukaemia

“…21 Therefore complex chromosomal rearrangements are necessary for a 5ЈMLL-3ЈAF10 fusion to occur and a transcribable reciprocal fusion is unlikely. 22,23 CALM is, however, transcribed in the same orientation as AF10, and a legitimate reciprocal translocation is more likely to occur.…”

Cryptic rearrangement involving MLL and AF10 occurring in utero

“…3 Thus, complex chromosomal rearrangements, requiring at least three breaks are required for an in-frame 5 0 MLL-3 0 AF10 fusion to occur. 4 Although these rearrangements are usually visible at the cytogenetic level, as is illustrated by this case, they can occasionally be cryptic underlining the importance of using FISH in addition to G-banding to characterise leukaemia-associated cytogenetic changes.…”

Solution structure of the nonmethyl‐CpG‐binding CXXC domain of the leukaemia‐associated MLL histone methyltransferase

“…With the structure of the CXXC domain now available, it will be possible to design nondisruptive mutations that can help to define the role of individual residues in these activities, and thus promoting a deeper understanding of the role of the CXXC domain in transformation by MLL fusion proteins. The CXXC domain is retained in all forms of leukaemogenic MLL fusion proteins, including partial tandem duplications (Lochner et al , 1996) and internal PHD finger 1 deletions (Chaplin et al , 2001; von Bergh et al , 2001; Deveney et al , 2003; Morel et al , 2003). Thus, novel approaches to the treatment of MLL‐associated leukaemias might involve addressing the continued occupancy of key target genes by MLL fusion proteins by disrupting the interaction between the CXXC domain and nonmethyl‐CpG DNA.…”

Identification and molecular characterisation of a CALM-AF10 fusion in acute megakaryoblastic leukaemia

“…21 Therefore complex chromosomal rearrangements are necessary for a 5ЈMLL-3ЈAF10 fusion to occur and a transcribable reciprocal fusion is unlikely. 22,23 CALM is, however, transcribed in the same orientation as AF10, and a legitimate reciprocal translocation is more likely to occur.…”

Cryptic rearrangement involving MLL and AF10 occurring in utero

“…3 Thus, complex chromosomal rearrangements, requiring at least three breaks are required for an in-frame 5 0 MLL-3 0 AF10 fusion to occur. 4 Although these rearrangements are usually visible at the cytogenetic level, as is illustrated by this case, they can occasionally be cryptic underlining the importance of using FISH in addition to G-banding to characterise leukaemia-associated cytogenetic changes.…”

Solution structure of the nonmethyl‐CpG‐binding CXXC domain of the leukaemia‐associated MLL histone methyltransferase

“…With the structure of the CXXC domain now available, it will be possible to design nondisruptive mutations that can help to define the role of individual residues in these activities, and thus promoting a deeper understanding of the role of the CXXC domain in transformation by MLL fusion proteins. The CXXC domain is retained in all forms of leukaemogenic MLL fusion proteins, including partial tandem duplications (Lochner et al , 1996) and internal PHD finger 1 deletions (Chaplin et al , 2001; von Bergh et al , 2001; Deveney et al , 2003; Morel et al , 2003). Thus, novel approaches to the treatment of MLL‐associated leukaemias might involve addressing the continued occupancy of key target genes by MLL fusion proteins by disrupting the interaction between the CXXC domain and nonmethyl‐CpG DNA.…”

Identification and molecular characterisation of a CALM-AF10 fusion in acute megakaryoblastic leukaemia

“…21 Therefore complex chromosomal rearrangements are necessary for a 5ЈMLL-3ЈAF10 fusion to occur and a transcribable reciprocal fusion is unlikely. 22,23 CALM is, however, transcribed in the same orientation as AF10, and a legitimate reciprocal translocation is more likely to occur.…”