V(D)J recombinase mediated inter-chromosomalHPRT alterations at cryptic recombination signal sequences in peripheral human T cells

Abstract

The V(D)J recombinase enzyme complex is responsible for the development of a diverse immune system by catalyzing intra-molecular rearrangements of immunoglobulin (Ig) and T cell receptor (TCR) genes at specific recombination signal sequences (RSSs). This enzyme complex has also been implicated in mediating pathologic and non-pathologic intra-and inter-molecular genomic rearrangements at cryptic (Ψ) RSSs outside the immune system loci in lymphoid cells. We describe here two V(D)J recombinase mediated genomic rearrangements resulting in alterations at the HPRT locus in human T-cells. These are interchromosomal insertions in which DNA fragments are inserted at breakpoints generated by V(D)J recombinase cleavage at Ψ RSS sites in the HPRT locus at Xq26. In the first, a TCR α signal ended segment from chromosome 14q11 is inserted at a Ψ RSS in intron 1 of the HPRT locus. In the second, a DNA fragment from 9q22 is integrated between the coding ends generated by a V(D)J recombinase mediated HPRT deletion. Identification of these in vivo V(D)J mediated inter-chromosomal insertions at Ψ RSSs in the HPRT gene supports the accumulating evidence that V(D)J recombinase can mediate mutagenic rearrangements in humans with potential pathologic consequences.

Breakpoint sites disclose the role of the V(D)J recombination machinery in the formation of T-cell receptor (TCR) and non-TCR associated aberrations in T-cell acute lymphoblastic leukemia

“…HPRT1 has frequently been shown to carry a complex deletion/insertion rearrangement, where gross regions of the TCRA locus are inserted into the HPRT1 locus. 28,30,96 One of the three TCRA insertions identified in this study (the BP site of 2 other cases could not be identified) showed involvement of a cRSS at the HPRT1 locus (Table 3). A BICD insertion (9q22) into HPRT1 locus has also been described.…”

“…5 Non TCRassociated chromosomal aberrations such as deletional aberrations (SIL-TAL1) and insertions (HPRT1) have also been appointed as V(D)J recombination-mediated events based on the presence of cRSSs at BP sites. [28][29][30][31] Until now, TCR-associated translocation mechanisms have mainly been evaluated for only a few BP sites by means of ex vivo experiments, 4,6,31,32 basically confirming the concept of RAG mistargeting to cRSSs. These oncogenes and their respective BP sites were usually chosen for their high frequency in T-ALL and also because of the probability that they would function as a cRSS based on structural criteria.…”

“…HPRT1 related insertions, though not directly implicated in T-ALL leukemogenesis, do occur in normal peripheral T-lymphocytes. 28,30,95 Even though these insertions do not seem to have direct oncogenic effect, we did analyze them to delineate the mechanism involved. HPRT1 has frequently been shown to carry a complex deletion/insertion rearrangement, where gross regions of the TCRA locus are inserted into the HPRT1 locus.…”

“…28,30 Even though such cRSS-cRSS interactions have not yet been identified in T-ALL, involvement of the V(D)J recombination machinery in the formation of these aberrations is evident based on the presence of cRSSs at the BP sites and the insertion of untemplated nucleotides at the junctions. 28,30 Comprehensive classification of TCR and non-TCR aberrations with respect to the role of the V(D)J recombination mechanism Collectively, our findings indicate that the V(D)J recombination mechanism can also be involved in non-TCR aberrations, and in particular cases, potentially even in non-cRSS associated aberrations. Despite the fact that cRSS-cRSS interactions have not been observed in T-ALL so far, they are comparable to 'Type 1' (RSS-cRSS) recombinations.…”

V(D)J recombination: Born to be wild

“…Intermolecular recombinations possess a characteristic signal junction, where one of the signal ends of the integrating fragment is precisely fused to a genomic RS. The other RS is fused to DNA immediately flanking the genomic RS (pseudo-hybrid junction) [19, 21, 24, 25] (Figure 2b, Table 1). As characterized in detail by the Nadel group [21], such events are probably mediated by intermolecular recombination (or recombination in trans ): a V(D)J recombination between the extrachromosomal RS in the signal end fragment and the genomic RS.…”