Characterization of NUMB as a Regulator of Anaplastic Lymphoma Kinase

Cellular events rely on protein-protein interactions that are often mediated by modular domains which recognize particular sequence motifs in binding partners. The NUMB protein is the first described cell fate determinant and multifaceted adaptor that is involved in a wide variety of cellular events. NUMB mainly mediates protein interactions via its modular PTB domain. Here we present a systematic investigation of the NUMB-PTB interactome by employing an integrative strategy combining both protein and peptide arrays. We profiled NUMB-PTB binding specificity and interacting proteins genome-wide. The receptor tyrosine kinases (RTKs) are found highly enriched in the interactome, raising the possibility that NUMB may act as a universal binding partner of RTKs. To further validate this hypothesis, we focused on the interaction between NUMB and Anaplastic Lymphoma Kinase (ALK), which promotes oncogenesis in a number of cancer types. Consistent with the prediction based on our proteomic study, NUMB-PTB directly binds to two motifs in ALK in vitro and in vivo. Intriguingly, functional analysis reveals that NUMB-ALK interaction regulates ALK activity antagonistically in an isoform dependent manner, by directing ALK to distinct post-endocytic trafficking destinations. Our study provides mechanistic insight into ALK regulation, explains the controversial behaviors of NUMB in tumorigenesis at the molecular level, and further reveals a biomarker of potential clinical value