Phosphorylation of Beclin 1 by BCR ABL suppresses autophagy in CML Abstract: The constitutively active chimeric tyrosine kinase BCR ABL is critical for initiation progression and maintenance of chronic myelogenous leukemia (CML). Imatinib and second generation BCR ABL tyrosine kinase inhibitors (TKIs) serve now as standard therapies for Ph+ patients. However disease persistence occurs frequently and one of the major reasons was considered to be insensitivity of CML stem cells to TKI treatment.<br>Recently accumulated evidence argues that autophagy a genetically regulated process of adaptation to metabolic stress is involved in TKI induced cell death. It is hypothesized that TKI induced autophagy could allow CML stem cells to become metabolically dormant enabling their survival under conditions that may mimic growth factor deprivation and thereby counter TKI induced cell death. However the molecular mechanism of TKI induced autophagy in BCR ABL+ CML as well as its role in malignant progression is poorly understood.<br>It has been shown that autophagy functions in CML in vitro however les is known in vivo. This study aimed to identify the precise role of autophagy and its effector molecules in a murine CML model. To identify the impact of autophagy in BCR ABL driven leukemia a targeted genetic approach to knockdown Beclin 1 as a key regulator of autophagy in a CML mouse model was used. Interestingly mice transplanted BCR ABL expressing bone marrow harboring Beclin 1 knockdown showed a less aggressive disease with significantly lower WBC count leukemic burden and prolonged overall survival of the mice compared to mice transplanted with BCR ABL + Beclin 1 WT BM. <br>To further test whether BCR ABL regulates autophagy LC3 was measured as a marker for autophagy in BCR ABL+ K562 cell. Interestingly inhibition of BCR ABL activity by nilotinib led to increased LC3 II expression and punctual LC3 accumulation indicating that BCR ABL activity can suppress autophagy. Next the proteins involved in BCR ABL mediated autophagosome formation were investigated. Recruitment of VPS34 UVRAG and ATG14 to Beclin 1 was increased in case of nilotinib treatment and could thereby positively regulate autophagosome formation whereas Rubicon a negative regulator was recruited less frequently to the Beclin 1 complex.<br>To further clarify the function of Beclin 1 biochemical analyses were performed. It showed that Beclin 1 binds to BCR ABL independent of BCR ABL kinase activity and Beclin 1 is phosphorylated by BCR ABL. To test t ...