UC San Diego

This study focused on understanding the subcellular distribution of the oncogenic TRK-T3 fusion protein. TRK-T3 results from a chromosomal translocation event, where the gene encoding for TFG is spliced onto the NTRK1 locus. The resulting TFG-NTRK1 fusion induces growth factor signaling and cell transformation. To investigate the molecular mechanism and how this occurs, recombinant TRK-T3-SNAP constructs were cloned. The subcellular distribution of the fusion protein was investigated by transfection and overexpression of TRK-T3-SNAP at varying levels, and robustly resulted in the formation of nanoscale foci, reminiscent of protein aggregates. Live-cell microscopy revealed that these foci are not aggregates, but rather dynamic structures that resemble biomolecular condensates. Fluorescence Recovery After Photobleaching (FRAP) approaches support the fluidity of TRK-T3 foci, prompting the hypothesis that aggregation of TRK-T3 results in ligand-free activation of the Receptor Tyrosine Kinase pathway (RTK) via the close juxtaposition of kinase domains and induction of autophosphorylation reactions within the putative condensate. Finally, TRK-T3 condensates did not colocalize with endogenous markers of the early secretory pathway, suggesting that the oncoprotein may form distinct signaling compartments in the cytosol of cells expressing the fusion protein.