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Molecular analysis of simple variant translocations in acute promyelocytic leukemia
1Somatic Cell Genetics Laboratory, Imperial Cancer Research Fund, London, UK.
Abstract:
The primary cytogenetic abnormality in acute promyelocytic leukemia (APL; FAB M3) is a reciprocal translocation, t(15;17)(q22;q12), which serves to fuse the PML gene on chromosome 15 to the retinoic acid receptor alpha (RARA) gene on chromosome 17. A PML-RARA fusion message transcribed from the der(15) is thought to mediate leukemogenesis. Two APL patients with simple variants of this translocation, t(3;15)(q21;q22) and t(X;15)(p11;q22), have previously been reported who lack cytogenetic involvement of chromosome 17, although their breakpoint positions on chromosome 15 still suggest the involvement of the PML gene. Here we report on a combined analysis by molecular genetics and in situ hybridization of these two patients, in which we wanted to determine whether the PML gene has alternative fusion partners or whether cryptic rearrangement of the RARA locus has occurred instead. A cryptic involvement of RARA was demonstrated in both patients by a combination of Southern analysis, reverse transcription coupled to PCR (RT-PCR), and fluorescence in situ hybridization. The results indicate an absolute requirement for the rearrangement of the RARA gene in the pathogenesis of APL and underline the importance of RARA during normal myeloid differentiation.
Insights
Acute promyelocytic leukemia (APL) typically involves the PML and RARA genes. This study found that even without direct chromosome 17 involvement, RARA gene rearrangement is crucial for APL development.
Area of Science:
- Hematology
- Molecular Genetics
- Cancer Biology
Background:
- Acute promyelocytic leukemia (APL) is characterized by the t(15;17) translocation, fusing PML and RARA genes.
- Variant translocations lacking direct chromosome 17 involvement have been reported in APL.
- The role of RARA in these variant cases remains to be fully elucidated.
Purpose of the Study:
- To investigate the involvement of the RARA gene in two APL patients with variant translocations not involving chromosome 17.
- To determine if PML has alternative fusion partners or if cryptic RARA rearrangements occur.
Main Methods:
- Combined molecular genetics and in situ hybridization analyses.
- Southern blot analysis.
- Reverse transcription coupled to PCR (RT-PCR).
- Fluorescence in situ hybridization (FISH).
Main Results:
- Cryptic rearrangement of the RARA locus was confirmed in both patients.
- Evidence of RARA involvement was demonstrated using Southern analysis, RT-PCR, and FISH.
- The PML gene was not found to have alternative fusion partners in these cases.
Conclusions:
- RARA gene rearrangement is essential for the pathogenesis of acute promyelocytic leukemia, even in variant translocations.
- This finding highlights the critical role of RARA in normal myeloid differentiation.