The t(15;17) breakpoint in acute promyelocytic leukemia cluster within two different sites of the myl gene: targets for the detection of minimal residual disease by the polymerase chain reaction

Abstract

The retinoic acid receptor alpha (RAR alpha) and the myl gene are involved in the translocation breakpoint t(15;17)(q22;q21) in acute promyelocytic leukemia (APL). The majority of the breakpoint sites have been mapped within the second intron of the RAR alpha gene; however, the breakpoint sites on the myl gene are variable. Using primer sets derived from exon 2 or exon 3 of the RAR alpha gene and a primer derived from the myl cDNA, we were able to amplify the breakpoint sites of the fusion transcripts of all six APL RNA samples by the reverse transcriptase-polymerase chain reaction (RT-PCR). A DNA fragment of 290 bp (breakpoint A) was amplified using RNA samples from three patients, whereas two DNA fragments of 630 and 774 bp (breakpoint B) were amplified using RNA samples from the other three APL patients. DNA sequence analysis of the amplified fragments suggests that the APL breakpoints clustered within two different introns of the myl gene. Northern blot analysis demonstrated that fusion transcripts RAR alpha/myl and myl/RAR alpha of varying sizes were detected in patients with different breakpoint sites on the myl gene. In addition, we analyzed five APL samples in complete remission and detected t(15;17)- positive cells. We conclude that the t(15;17) breakpoints in APL can be amplified by PCR using a single primer set and that minimal residual disease can be demonstrated in APL using RT-PCR.

Retinoids in the treatment of acute promyelocytic leukemia

“…Thus, the RA and DNA binding sites of RAR-ex are maintained in the fusion protein (25,34). These rearrangements were confirmed by other scientists (1,9,10,51) showing that they were found in almost all patients with APL and therefore involved in leukemogenesis. The response to RA seems to be associated with the expression of this aberrant PMLlRAR-ex mRNA, although the physiological reason for this association is unclear (51).…”

Postconsolidation Maintenance and Monitoring in Patients With Acute Promyelocytic Leukemia

“…23,24 In the early 1990s, several retrospective studies showed that reverse transcriptase-PCR (RT-PCR) analysis of the PML/RARα fusion gene product can detect residual leukemic cells during hematologic remission in patients with APL. [25][26][27][28] Furthermore, it was shown retrospectively that patients who remain PCR-positive after consolidation therapy 29 or who transformed from PCR-negative to PCRpositive 30 almost always experience a relapse. The GIMEMA group was the first to report prospectively about the natural history of molecular relapse.…”

Acute promyelocytic leukemia: a curable disease

“…The prognostic value of detecting MRD during clinical remission was initially suggested in Italy in 1992 131 and successively confirmed in numerous studies conducted in China, USA, Japan and several European countries. [132][133][134][135][136][137][138][139][140][141][142][143] Studies performed by using PCR assays capable of detecting one leukemic cell in a background of 10 3 -10 4 normal cells, agreed that a positive PCR test at completion of consolidation is strongly associated with impending clinical relapse. On the contrary, negative tests are not always associated with prolonged DFS and cure.…”

“…In fact, a sizable proportion of patients who had tested negative post-consolidation were reported in the same studies to have relapsed thereafter. [131][132][133][134][135][136][137][138][139][140][141][142][143] Notwithstanding, it is worth noting that no patients in long-term survival are found PCRpositive using this sensitivity threshold. [131][132][133][134][135][136][137][138][139][140][141][142][143] This clearly indicates that a status of PML/RAR␣ PCR negativity is our best presently available therapeutic goal.…”