Polarized distribution of Bcr-Abl in migrating myeloid cells and co-localization of Bcr-Abl and its target proteins

Bcr-Abl plays a critical role in the pathogenesis of Philadelphia chromosom e-positive leukemia. Although a large number of substrates and interacting proteins of Bcr-Abl have been identified, it remains unclear whether Bcr-Ab l assembles multi-protein complexes and if it does where these complexes ar e within cells. We have investigated the localization of Bcr-Abl in 32D mye loid cells attached to the extracellular matrix. We have found that Bcr-Abl displays a polarized distribution, colocalizing with a subset of filamento us actin at trailing portions of migrating 32D cells, and localizes on the cortical F-actin and on vesicle-like structures in resting 32D cells. Delet ion of the actin binding domain of Bcr-Abl (Bcr-Abl-AD) dramatically enhanc es the localization of Bcr-Abl on the vesicle-like structures. These distin ct localization patterns of Bcr-Abl and Bcr-Abl-AD enabled us to examine th e localization of Bcr-Abl substrate and interacting proteins in relation to Bcr-Abl. We found that a subset of biochemically defined target proteins o f Bcr-Abl redistributed and co-localized with Bcr-Abl on F-actin and on ves icle-like structures. The co-localization of signaling proteins with Bcr-Ab l at its sites of localization supports the idea that Bcr-Abl forms a multi -protein signaling complex, while the polarized distribution and vesicle-li ke localization of Bcr-Abl may play a role in leukemogenesis.