The last shall be first

LINE-I element insertion at the t(11;22) translocation breakpoint of a desmoplastic small round cell tumor

A t(11;22)(p13;p12) chromosomal translocation, juxtaposing the Wilms' tumor (WT1) and Ewing's sarcoma (EWS) genes, is the cytogenetic hallmark of desmoplastic small round cell tumor (DSRCT), a primitive multiphenotypic sarcoma arising in serosal tissues. Chimeric transcripts generated by this rearrangement encode an aberrant transcription factor that fuses the 5' region of EWS with a 3' WT1 segment. We describe the insertion of a LINE-I DNA mobile genetic element at the genomic breakpoint of a DSRCT chromosomal translocation. A 480 bp heterologous DNA segment with homology to the LINE-I DNA consensus sequence was located between EWS intron 8 and WT1 exon 8 in the productively rearranged allele. Sequence homology corresponded to the LINE-I ORF-2, which encodes a protein with reverse-transcriptase activity. The heterologous inserted fragment was not evident in the germline of normal tissue from the patient, suggesting that transposition occurred in somatic cells, possibly during the process of chromosomal rearrangement. This case represents the first example of LINE-I DNA transposition at the fusion site of a tumor-associated chromosomal rearrangement.

The role of mitotic recombination in carcinogenesis

Genetic recombination systems are present in all living cells and viruses and generally contribute to their hosts' flexibility with respect to changing environmental conditions. Recombination systems not only help highly developed organisms to protect themselves from microbial attack via an elaborate immune system, but conversely, recombination systems also enable microorganisms to escape from such an immune system. Recombination enzymes act with a high specificity on DNA sequences that either exhibit extended stretches of homology or contain characteristic signal sequences. However, recombination enzymes may rarely act on incorrect alternative target sequences, which may result in the formation of chromosomal deletions, inversions, translocations, or amplifications of defined DNA regions. This review describes the characteristics of several recombination systems and focuses on the implication of aberrant recombination in carcinogenesis. The consequences of mitotic recombination on the inappropriate activation of protooncogenes and on the loss of tumor suppressor genes is discussed. Cases are reported where mitotic recombination clearly has been associated with carcinogenesis in rodents as well as humans. Several test systems able to detect recombinagenic activities of chemical compounds are described.

Fusion of the dominant negative transcription regulator CHOP with a novel gene FUS by translocation t(12;16) in malignant liposarcoma

The search for tumour-specific markers is one of the chief goals in cancer biology. We show that the translocation t(12;16)(q13:p11) in malignant myxoid liposarcoma can be a fusion of the CHOP dominant negative transcription factor gene with a novel gene, FUS, which can result in fusion of the FUS glycine-rich protein with the whole CHOP coding region. The data support the concept that protein fusion may commonly occur in solid tumours resulting in tumour-specific markers of potential clinical importance. The data also indicate the importance of transcription disruption in the pathogenesis of solid tumours.