UC San Diego

Neurotrophic receptor tyrosine kinases (NTRKs) belong to the receptor tyrosine kinase (RTK) family. NTRKs are responsible for the activation of multiple downstream signaling pathways that regulate cell growth, proliferation, differentiation, and apoptosis. NTRK-associated mutations lead to aberrant activation of these downstream pathways and often result in oncogenesis. This study characterizes the NACC2-NTRK2 oncogenic fusion protein that leads to pediatric astrocytoma and glioblastoma. This fusion joins the broad-complex, tramtrack, and bric-a-brac (BTB) domain of Nucleus Accumbens-associated protein 2 (NACC2) with the transmembrane helix and tyrosine kinase domain of NTRK2. This work focuses on identifying domains critical to the fusion protein activity and possible methods to deactivate the fusion. NACC2-NTRK2 is able to transform NIH3T3 cells. Such activity depends on the NTRK2 kinase domain phosphorylation that activates signaling pathways including MAPK, JAK/STAT, and PLCγ. The activation of the NTRK2 kinase domain relies on the multimerization of the NACC2 BTB domain. A BTB domain charged pocket mutation and a monomer core mutation result in deactivation of the kinase domain and abrogates the ability to transform NIH3T3 cells, suggesting that BTB domain inhibition could be a potential treatment for the NACC2-NTRK2 induced cancer. The undefined region of NACC2 at residues 120-418 is responsible for forming stronger multimers. Once removed, the NACC2-NTRK2 multimer is vulnerable to SDS denaturation and leads to reduced activity of the fusion. Lastly, the removal of the transmembrane helix leads to higher activation of the NACC2-NTRK2 fusion. A protein stability assay indicates that transmembrane deletion prevents NACC2-NTRK2 degradation.