Bcr interacts with components of the endosomal sorting complex required for transport-I and is required for epidermal growth factor receptor turnover.

Virtually all patients with chronic myelogenous leukemia (CML) express an aberrant protein (p210 Bcr-Abl) that contains NH2-terminal sequences from Bcr fused to COOH-terminal sequences from Abl. In a yeast two-hybrid screen, we have identified TSG101 as a binding partner for Bcr. Because TSG101 is a subunit of the mammalian endosomal sorting complex required for transport (ESCRT), which regulates protein sorting during endosomal trafficking, this association suggests that Bcr may have a related cellular function. The docking site for TSG101 has been mapped to the COOH terminus of Bcr, indicating that this interaction may be disrupted in CML. Overexpression studies with full-length TSG101 and Bcr reveal that this interaction can be recapitulated in mammalian cells. The association can also be observed between natively expressed proteins in a panel of hematopoietic and nonhematopoietic cell lines, where a second subunit of the ESCRT complex, vacuolar sorting protein 28 (Vps28), was also found to interact with Bcr. Both Bcr and TSG101 exhibit a punctate cytoplasmic distribution and seem to colocalize in HeLa cells, which would be consistent with an in vivo association. Bacterially purified Bcr and TSG101 also bind, suggesting that the interaction is direct and is not dependent on ubiquitination. Disruption of the endosomal pathway with an ATPase-defective Vps4 mutant results in the cellular redistribution of Bcr, and suppression of Bcr in HeLa cells by small interfering RNA impairs epidermal growth factor receptor turnover. Taken together, these observations suggest that Bcr is a component of the mammalian ESCRT complexes and plays an important role in cellular trafficking of growth factor receptors.