Targeting RAD51 phosphotyrosine-315 to prevent unfaithful recombination repair in BCR-ABL1 leukemia.

Chronic myeloid leukemia chronic phase (CML-CP) CD34(+) cells contain numerous DNA double-strand breaks whose unfaithful repair may contribute to chromosomal instability and disease progression to blast phase (CML-BP). These phenomena are often associated with the appearance of imatinib-resistant BCR-ABL1 kinase mutants (eg, T315I) and overexpression of BCR-ABL1. Here we show that BCR-ABL1 (nonmutated and T315I mutant) promoted RAD51 recombinase-mediated unfaithful homeologous recombination repair (HomeoRR) in a dosage-dependent manner. BCR-ABL1 SH3 domain interacts with RAD51 proline-rich regions, resulting in direct phosphorylation of RAD51 on Y315 (pY315). RAD51(pY315) facilitates dissociation from the complex with BCR-ABL1 kinase, migrates to the nucleus, and enhances formation of the nuclear foci indicative of recombination sites. HomeoRR and RAD51 nuclear foci were strongly reduced by RAD51(Y315F) phosphorylation-less mutant. In addition, peptide aptamer mimicking RAD51(pY315) fragment, but not that with Y315F phosphorylation-less substitution, diminished RAD51 foci formation and inhibited HomeoRR in leukemia cells. In conclusion, we postulate that BCR-ABL1 kinase-mediated RAD51(pY315) promotes unfaithful HomeoRR in leukemia cells, which may contribute to accumulation of secondary chromosomal aberrations responsible for CML relapse and progression.