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Genomic variability and alternative splicing generate multiple PML/RAR alpha transcripts that encode aberrant PML
P P Pandolfi1, M Alcalay, M Fagioli
1Istituto Clinica Medica I, University of Perugia, Italy.
Abstract:
The acute promyelocytic leukaemia (APL) 15;17 translocation generates a PML/RAR alpha chimeric gene which is transcribed as a fusion PML/RAR alpha mRNA. Molecular studies on a large series of APLs revealed great heterogeneity of the PML/RAR alpha transcripts due to: (i) variable breaking of chromosome 15 within three PML breakpoint cluster regions (bcr1, bcr2 and bcr3), (ii) alternative splicings of the PML portion and (iii) alternative usage of two RAR alpha polyadenylation sites. Nucleotide sequence analysis predicted two types of proteins: multiple PML/RAR alpha and aberrant PML. The PML/RAR alpha proteins varied among bcr1, 2 and 3 APL cases and within single cases. The fusion proteins contained variable portions of the PML N terminus joined to the B-F RAR alpha domains; the only PML region retained was the putative DNA binding domain. The aberrant PML proteins lacked the C terminus, which had been replaced by from two to ten amino acid residues from the RAR alpha sequence. Multiple PML/RAR alpha isoforms and aberrant PML proteins were found to coexist in all APLs. These findings indicate that two potential oncogenic proteins are generated by the t(15;17) and suggest that the PML activation pathway is altered in APLs.
Insights
The 15;17 translocation in acute promyelocytic leukemia (APL) creates diverse PML/RAR alpha fusion proteins. These variations arise from multiple breakpoint regions, alternative splicing, and polyadenylation, impacting PML activation pathways.
Area of Science:
- Molecular Biology
- Hematology
- Oncology
Background:
- Acute promyelocytic leukemia (APL) is characterized by the t(15;17) translocation.
- This translocation results in a PML/RAR alpha chimeric gene and fusion mRNA.
Purpose of the Study:
- To investigate the heterogeneity of PML/RAR alpha transcripts in APL.
- To identify the types and variations of proteins generated by the t(15;17) translocation.
Main Methods:
- Molecular studies on a large series of APL patients.
- Nucleotide sequence analysis of PML/RAR alpha transcripts.
- Analysis of protein structures, including breakpoint regions and domains.
Main Results:
- Identified significant heterogeneity in PML/RAR alpha transcripts due to variable breakpoints (bcr1, bcr2, bcr3), alternative splicing, and polyadenylation.
- Predicted two protein types: PML/RAR alpha and aberrant PML, with variations in both.
- Found multiple PML/RAR alpha isoforms and aberrant PML proteins coexisting in all APL cases.
Conclusions:
- The t(15;17) translocation generates diverse PML/RAR alpha and aberrant PML proteins.
- These protein variations contribute to the molecular complexity of APL.
- The findings suggest alterations in the PML activation pathway are central to APL pathogenesis.