transcription factor fusion genes
Chromosomal rearrangements that disrupt transcription factor genes can result in fusion proteins with enhanced or aberrant transcriptional activity or fusion proteins that mediate transcriptional repression.
Enhanced or aberrant transcriptional activity
A fusion protein with enhanced or aberrant transcriptional activity is present in virtually all cases of Ewing’s sarcoma, in which unique translocations — t(11;22)(q24;q12) and t(21;22)(q22;q12) — fuse the EWSR1 gene on band 22q12.2 to a gene encoding a member of the ETS family of transcription factors, most frequently FLI1 on band 11q24.1-q24.3 (in approximately 85% of patients) and ERG on band 21q22.3 (in approximately 10% of patients).
The resulting chimeric transcription factors retain the DNA-binding domain of the respective ETSs family member and possess, in the EWSR1 portion of the fusion protein, a potent transactivation domain that induces the transcription of various genes whose aberrant expression appears to be required for EWSR1-ETSs–mediated tumor growth.
Aberrant transcriptional repression
Chromosomal rearrangements that entail aberrant transcriptional repression occur in a substantial proportion of patients with acute myeloid leukemia.
For example, the chimeric proteins resulting from fusion genes such as PML-RARA, RUNX1-RUNX1T1, and CBFB-MYH11 all contain a transcription factor that retains its DNA-binding motif and an unrelated protein that interacts with inhibitors of gene transcription.
As a result, binding of the chimeric transcription factors to their target genes, which include genes required for normal myeloid differentiation, causes aberrant transcriptional repression, thereby contributing to the accumulation of immature myeloid cells in acute myeloid leukemia.
Therapeutics
Selective inhibition of the abnormal transcriptional activity has proved to be a less tractable pharmacologic goal than inhibition of constitutive tyrosine kinase activity. As a consequence, approaches to specific targeting of overactive transcription factors have not yet reached clinical development.
One of the fusion proteins associated with transcriptional repression has been targeted with success in the clinic. In acute promyelocytic leukemia, all-trans retinoic acid and arsenic trioxide reverse the transcriptional repression caused by the PML-RARA fusion protein by forcing the release of transcription inhibitors from the fusion protein or stimulating degradation of PML-RARA or both. These two drugs are remarkably effective in acute promyelocytic leukemia.
Examples
| tumoral translocations | - | - | - |
| t(1;22)(p13;q13) | RBM15-MKL1 | acute megakaryoblastic leukemia | - |
| t(2;3)(q12-q14;p25) | PAX8-PPARG | follicular thyroid cacrcinoma | - |
| t(7;11)(p15-p14;p15) | NUP98-HOXA9 | myelodysplastic syndrome, acute myeloid carcinoma | - |
| t(8;21)(q22;q22) | RUNX1-RUNX1T1 | acute myeloid leukemia | |
| t(9;11)(p22;q23) | MLL-MLLT3 | acute myeloid leukemia | - |
| t(11;22)(q24;q12) | FLI1-EWSR1 | Ewing sarcoma, EFTs | - |
| t(12;21)(p13;q22) | ETV6-RUNX1 | acute lymphoblastic leukemia | - |
| t(15;17)(q22;q21) | PML-RARA | acute promyelocytic leukemia | all-trans retinoic acid, arsenic trioxide |
| t(21;22)(q22;q12) | ERG-EWSR1 | Ewing sarcoma, EFTs | - |
| tumoral inversions | - | - | - |
| inv(16)(p13q22) | CBFB-MYH11 | acute myeloid leukemia | - |
See also
fusion genes
- fusion genes involving tyrosine kinases