3265 – STRUCTURAL IDENTIFICATION OF MAJOR MOLECULAR DETERMINANTS FOR PHOSPHOTYROSINE RECOGNITION IN TYROSINE KINASES REVEALS TUMOR PROMOTING AND SUPPRESSIVE FUNCTIONS

Abstract

Breakpoint cluster region-Abelson (BCR-ABL)+ leukemia is a prototypical kinase-driven malignancy in which tyrosine kinase inhibitors have improved outcomes, yet resistant chronic myeloid leukemia (CML), blast-phase CML, and Philadelphia+ acute lymphoblastic leukemia remain major therapeutic challenges. Current BCR-ABL inhibitors suppress BCR-ABL signaling globally, without distinguishing substrates that promote leukemia from those that may restrain disease progression.

Protein tyrosine kinases phosphorylate tyrosine residues in their substrates, an activity hijacked in leukemia to sustain oncogenic signaling. We recently found that, beyond conventional phosphotyrosine (pTyr)-dependent signaling through phosphobinding modules, Abl and several other kinases can directly recognize a pTyr adjacent to the phospho-acceptor tyrosine, thereby generating twin pTyr-pTyr sites.

Using structure-guided protein engineering and substrate-specificity profiling, we created Abl variants with graded pTyr-recognition activity and disrupted phosphoprimed recognition without abolishing kinase function. In BCR-ABL-driven mouse leukemia models, hypomorphic loss-of-function variants showed slower disease progression, whereas neomorphic phosphopriming-deficient variants drove faster and more aggressive myeloproliferative disease. Contrary to current dogma, these findings suggest that a subset of phosphoprimed twin pTyr-pTyr substrates downstream of BCR-ABL suppresses leukemogenesis in vivo.

Together, our data revealed a previously unappreciated leukemia-suppressive signaling layer downstream of BCR-ABL and suggest that twin pTyr-pTyr signaling diversifies oncogenic kinase outputs in hematologic malignancies. This distinction may inform more precise therapeutic strategies that target disease-promoting BCR-ABL signaling while preserving, or exploiting, disease-restraining pathways.

Breakpoint cluster region-Abelson (BCR-ABL)+ leukemia is a prototypical kinase-driven malignancy in which tyrosine kinase inhibitors have improved outcomes, yet resistant chronic myeloid leukemia (CML), blast-phase CML, and Philadelphia+ acute lymphoblastic leukemia remain major therapeutic challenges. Current BCR-ABL inhibitors suppress BCR-ABL signaling globally, without distinguishing substrates that promote leukemia from those that may restrain disease progression.

Protein tyrosine kinases phosphorylate tyrosine residues in their substrates, an activity hijacked in leukemia to sustain oncogenic signaling. We recently found that, beyond conventional phosphotyrosine (pTyr)-dependent signaling through phosphobinding modules, Abl and several other kinases can directly recognize a pTyr adjacent to the phospho-acceptor tyrosine, thereby generating twin pTyr-pTyr sites.

Using structure-guided protein engineering and substrate-specificity profiling, we created Abl variants with graded pTyr-recognition activity and disrupted phosphoprimed recognition without abolishing kinase function. In BCR-ABL-driven mouse leukemia models, hypomorphic loss-of-function variants showed slower disease progression, whereas neomorphic phosphopriming-deficient variants drove faster and more aggressive myeloproliferative disease. Contrary to current dogma, these findings suggest that a subset of phosphoprimed twin pTyr-pTyr substrates downstream of BCR-ABL suppresses leukemogenesis in vivo.

Together, our data revealed a previously unappreciated leukemia-suppressive signaling layer downstream of BCR-ABL and suggest that twin pTyr-pTyr signaling diversifies oncogenic kinase outputs in hematologic malignancies. This distinction may inform more precise therapeutic strategies that target disease-promoting BCR-ABL signaling while preserving, or exploiting, disease-restraining pathways.