Fine structure of translocation breakpoints in leukemic blasts with chromosomal translocation t(4;11): the DNA damage-repair model of translocation

Abstract

Chromosomal translocations t(4;11) are regularly associated with a speci®c type of acute leukemias and probably initiate the development of this disease. It has been proposed by others, that these translocations are mediated by recombinases of the immune system. The breakpoints on both derivative chromosomes for three t(4;11) leukemia-derived cell lines and primary blasts from two patients have been analysed here in detail. The results revealed that: (a) multiple double-or singlestranded DNA breaks must have occured near the translocation breakpoints on both participating chromosomes; and (b) DNA fragments¯anked by these breaks must have either been deleted, inverted or duplicated during the translocation process. We found no evidence for the involvement of speci®c target sequences and recombinases of the immune system. Similar characteristic features were observed by re-interpretation of published t(6;11) and t(9;22) translocation data. Therefore we present a new model for the generation of these translocations which poses, that these translocations are reciprocal but not balanced at the ®ne structure level and that the DNA damage-repair machinery is likely involved in producing the ®nal structure of the translocation breakpoint.

A DNA damage repair mechanism is involved in the origin of chromosomal translocations t(4;11) in primary leukemic cells

“…Based on this extended knowledge, it was possible to design a novel set of several dozen speci®c oligonucleotides and thus to amplify and sequence both reciprocal breakpoints for each patient. Unexpectedly, the analysis not only con®rmed the previous report describing leukemia-derived cell lines (Reichel et al, 1998), but it provided further evidence allowing us to specify the type of DNA repair involved. Characteristic signs for one of the several known DNA repair mechanisms, the`error-prone-repair' (EPR) pathway, were consistently observed.…”

“…However, until now this method was limited to provide information for only one of the two derivative chromosomes for each patient, because only a limited subset of PCR primers was available. Using both recently published and unpublished sequence information about the breakpoint cluster region of the AF-4 gene Reichel et al, 1998;E Gillert, unpublished data), it was now possible to select a suitable primer pair to amplify the corresponding reciprocal breakpoint for 10/14 patients (Figure 1). …”

“…Primer sets used for the ampli®cation process are speci®ed in the Materials and methods. Asterisk: presumably non-speci®c ampli®cation products ones already described for the leukemia-derived RS4;11 and LLM cell lines carrying a t(4;11) translocation (Reichel et al, 1998).…”

“…The same is true for the SIL-TAL deletion involved in a frequent form of T-cell leukemias, where nonamer and heptamer sequences were identi®ed at the chromosomal breakpoints (Breit et al, 1993). None of these characteristic signs were observed for t(4;11) translocations in leukemia-derived cell lines and a limited number of primary blasts (Marschalek et al, 1995Reichel et al, 1998). From the limited evidence to date it was concluded, that the illegitimate recombination leading to these translocations was probably initiated by a severe DNA damage and subsequent defects in the DNA repair mechanism (Reichel et al, 1998).…”

“…The analysis was greatly facilitated by the recent improvement of our knowledge of the breakpoint cluster regions of the MLL and AF-4 genes (Gu et al, 1994;Marschalek et al, 1995;Nilson et al, 1997;Reichel et al, 1998). Based on this extended knowledge, it was possible to design a novel set of several dozen speci®c oligonucleotides and thus to amplify and sequence both reciprocal breakpoints for each patient.…”