TNK1 is a ubiquitin-sensing kinase that can be targeted to block tumor growth.

Thirty-eight negative kinase-1 (TNK1) is an understudied non-receptor tyrosine kinase with no established function or mechanism of regulation. We recently identified TNK1 as the primary kinase driver of cell survival in subsets of patient blood cancer samples1 . We discovered that one unusual feature of TNK1 is a functional ubiquitin-association (UBA) domain that binds with high affinity to multiple poly-ubiquitin linkages. Our recent 1.5 angstrom crystal structure of the TNK1 UBA shows an atypical five-helix UBA domain with two predicted ubiquitin-binding interfaces. We found that TNK1 relies on its UBA domain to home to phase-separated poly-ubiquitylated protein condensates and becomes fully active at these sites. To our knowledge, this feature of TNK1-a bona-fide ubiquitin-association domain that promotes kinase activation-makes TNK1 unique across the human kinome. Our data also suggest that 14-3-3 interacts with a MARK-mediated phosphorylation at S502 of TNK1 to sequester the kinase away from ubiquitin and inhibit kinase activation. Thus, TNK1 toggles between poly-ubiquitin bound (active) and 14-3-3-bound (inactive) states. Our preliminary data suggest that the interaction with poly-ubiquitin at condensates tethers TNK1 to substrates, facilitating its phosphorylation of substrates involved in the lysosomal degradation of condensates. Furthermore, we found that patient mutations that truncate the 14-3-3 binding site and UBA domain convert TNK1 into a cancer driver with an altered substrate profile, skewed toward pro-growth substrates like STAT3. Finally, we show that mutant TNK1-driven tumors can be targeted in vivo with a novel anti-TNK1 small molecule. Thus, together our data suggest that TNK1 acts as a ubiquitin sensor and is a candidate for targeted therapy. 1. Chan TY and Egbert CM et al., (2021) TNK1 is a ubiquitin-binding and 14-3-3-regulated kinase that can be targeted to block tumor growth. Nature Communications(in press).