A mechanism of TNK1 activation by C-terminal gene truncation in human lymphomas.

Thirty-eight-negative kinase 1 (TNK1) is a poorly characterized non-receptor tyrosine kinase (NRTK) first isolated from umbilical cord blood. TNK1 differs from most NRTKs in that it possesses a functional ubiquitin association (UBA) domain at its C-terminus. We previously observed that the TNK1 UBA domain interacts with a variety of poly-ubiquitin chains, is essential for full TNK1 activation, and facilitates the clustering of active TNK1 into ubiquitin-rich condensates.1 Paradoxically, a genetic inversion that truncates the TNK1 C-terminus (including the UBA domain) in human lymphoma hyperactivates the kinase and coverts it into an oncogenic driver. Our current research focuses on how deletion of the UBA, which is important for native TNK1 function, helps activate the kinase. Here we show that immediately adjacent to the UBA domain on TNK1 is an inhibitory 14-3-3 binding site, which is also truncated in lymphoma. Furthermore, point mutations that disrupt the 14-3-3 binding site are sufficient to convert TNK1 into a hyperactive oncogenic kinase. In addition, we show that although truncation of the UBA perturbs the normal function of TNK1, it also stabilizes TNK1 protein levels. Thus, the lymphoma-associated truncations in TNK1 activate and stabilize the kinase, resulting in a highly expressed and active TNK1. Finally, we show that truncation of the 14-3-3 binding site and UBA domain of TNK1 is sufficient to transform pro-B cells to growth factor-independence and grow tumors in vivo. Thus, our data explain how genetic inversions convert TNK1 into an oncogenic driver in human cancers. 1. Chan, TY., Egbert, C.M., Maxson, J.E. et al. TNK1 is a ubiquitin-binding and 14-3-3-regulated kinase that can be targeted to block tumor growth. Nat Commun 12, 5337 (2021). https://doi.org/10.1038/s41467-021-25622-3.