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UBC Theses and Dissertations

Dissecting the mechanism of ETV6 polymerization Huang-Hobbs, Helen


ETV6 (or TEL), a member of the ETS family of eukaryotic transcription factors, normally functions as a transcriptional repressor and putative tumor suppressor. ETV6 is modular, containing a SAM (or PNT) domain and a DNA-binding ETS domain joined by a flexible linker sequence. The ETV6 SAM domain self-associates in a head-to-tail fashion, forming helical polymers proposed to generate extended repressive complexes at target DNA sites. ETV6 is also frequently involved in chromosomal translocations yielding unregulated chimeric oncoproteins with the SAM domain fused to the catalytic domain of a tyrosine receptor kinase such as NTRK3. Cellular transformation likely results from SAM domain-mediated polymerization and constitutive activation of the kinase domain. In the case of the ETV6- NTRK3 fusion (EN), this transformation is linked to congenital fibrosarcomas. Our goal is to investigate via mutations within its SAM domain, the thermodynamic and dynamic mechanisms underlying the altered transformation properties of ETV6-NTRK3. These studies have been carried out using monomeric variants of the isolated SAM domains with "head" or "tail" point mutations that prevent self-association, yet allow for formation of a mixed dimer with a native binding interface. Specifically, we used a combination of NMR spectroscopy and isothermal titration calorimetry to study the effects of additional mutations on their dimerization. Consistent with its involvement in a crystallographically-observed interdomain salt bridge, mutation of Lys99 was found to weaken the association of ETV-SAM monomers in solution, and to disrupt cellular transformation by EN. This supports the role of the SAM domain self-association in the activation of ETV6-NTRK3, and helps define the mechanisms underlying cellular transformation by similar chimeric oncoproteins.

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