3270 – UNDERSTANDING THE CELLULAR AND MOLECULAR CONSEQUENCES OF DISRUPTED TWIN PHOSPHOTYROSINE SIGNALING IN BCR-ABL-DRIVEN LEUKEMIA.

Abstract

Chronic myeloid leukemia (CML) and Philadelphia-positive acute lymphoblastic leukemia (ALL) are driven by expression of Breakpoint cluster region-Abelson (BCR-ABL), an oncogenic fusion protein that promotes aberrant myeloid expansion at the expense of normal hematopoiesis. Recent studies have shown that ABL kinase preferentially phosphorylates motifs containing a phosphotyrosine (pTyr) directly upstream of its target phospho-acceptor tyrosine. Previous work from our laboratory has identified the molecular determinant driving this pTyr-recognition and engineered mutants (BCR-ABL R328A and BCR-ABL R328M) that disrupt recognition of pTyr, preventing twin phosphotyrosine (pTyr-pTyr) signaling. Unexpectedly, these pTyr-recognition mutants accelerate myeloproliferative disease in vivo compared with BCR-ABL wild-type (WT), suggesting an important but unexplored role for pTyr-pTyr signaling in leukemogenesis. Here, we investigated the cellular and molecular consequences of disrupting BCR-ABL pTyr-pTyr signaling and their impact on leukemia development. Using the pTyr-deficient mutants, we showed that loss of pTyr-pTyr signaling alters BCR-ABL-induced differentiation dynamics and preserves a greater number of ckit+ hematopoietic progenitors. This is accompanied by enhanced serial replating capacity of transduced LSK cells and distinct transcriptional changes. Together, these findings revealed a previously uncharacterized signaling arm of BCR-ABL that may restrict leukemic progenitor self-renewal.

Chronic myeloid leukemia (CML) and Philadelphia-positive acute lymphoblastic leukemia (ALL) are driven by expression of Breakpoint cluster region-Abelson (BCR-ABL), an oncogenic fusion protein that promotes aberrant myeloid expansion at the expense of normal hematopoiesis. Recent studies have shown that ABL kinase preferentially phosphorylates motifs containing a phosphotyrosine (pTyr) directly upstream of its target phospho-acceptor tyrosine. Previous work from our laboratory has identified the molecular determinant driving this pTyr-recognition and engineered mutants (BCR-ABL R328A and BCR-ABL R328M) that disrupt recognition of pTyr, preventing twin phosphotyrosine (pTyr-pTyr) signaling. Unexpectedly, these pTyr-recognition mutants accelerate myeloproliferative disease in vivo compared with BCR-ABL wild-type (WT), suggesting an important but unexplored role for pTyr-pTyr signaling in leukemogenesis. Here, we investigated the cellular and molecular consequences of disrupting BCR-ABL pTyr-pTyr signaling and their impact on leukemia development. Using the pTyr-deficient mutants, we showed that loss of pTyr-pTyr signaling alters BCR-ABL-induced differentiation dynamics and preserves a greater number of ckit+ hematopoietic progenitors. This is accompanied by enhanced serial replating capacity of transduced LSK cells and distinct transcriptional changes. Together, these findings revealed a previously uncharacterized signaling arm of BCR-ABL that may restrict leukemic progenitor self-renewal.