Abstract 3489: TNK1 is a ubiquitin sensing kinase that can be targeted in vivo to block tumor growth
Authors: Lopez-Palacios Tania , Chan Tsz-Yin , Egbert Christina M. , Ashworth Spencer , Vaughan Alec , Forostyan Tanya V. , Siddiqui Adam , Foulks Jason M. , Moody James , Maxson Julia E. , Tyner Jeffrey W. , Warner Steven L. , Andersen Joshua Lyon 
Published: April 2023

Abstract
Thirty eight negative kinase 1 (TNK1) is an understudied non-receptor tyrosine kinase with no established function or mechanism of regulation. Our recent publication reported TNK1 as the primary kinase driver of cell survival in subsets of patient blood cancer samples. In an effort to understand TNK1 function and regulation, we discovered that it has an unusual C-terminal ubiquitin-association (UBA) domain that binds with high affinity to multiple poly-ubiquitin linkages. A 1.5 angstrom crystal structure of the TNK1 UBA shows an atypical five helix UBA domain with two ubiquitin-binding interfaces. Our data suggest that TNK1 relies on its UBA domain to localize to phase-separated ubiquitin-rich 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. We also show that the phospho-binding protein 14-3-3 interacts with a MARK-mediated phosphorylation at S502 within the proline-rich domain of TNK1 to sequester TNK1 away from ubiquitin condensates and inhibit kinase activation. In this way, 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 involved in the lysosomal degradation of the condensates via aggrephagy. 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 an anti-TNK1 small molecule. Together, our data provide a first mechanism of regulation and role for TNK1 as a ubiquitin sensor and implicate TNK1 as a candidate for targeted cancer therapy.
1. Chan TY*, Egbert CM*, Maxson JE, Siddiqui A, Larsen LJ, Kohler K, Balasooriya ER, Pennington KL, Tsang TM, Frey M, Soderblom EJ, Geng H, Müschen M, Forostyan TV, Free S, Mercenne G, Banks CJ, Valdoz J, Whatcott CJ, Foulks JM, Bearss DJ, O'Hare T, Huang DCS, Christensen KA, Moody J, Warner SL, Tyner JW, Andersen JL. (2021) TNK1 is a ubiquitin-binding and 14-3-3-regulated kinase that can be targeted to block tumor growth. Nature Communications, Sept 9;12(1):5337, PMID: 34504101, *co-first authors
Citation Format: Tania Lopez-Palacios, Tsz-Yin Chan, Christina M. Egbert, Spencer Ashworth, Alec Vaughan, Tanya V. Forostyan, Adam Siddiqui, Jason M. Foulks, James Moody, Julia E. Maxson, Jeffrey W. Tyner, Steven L. Warner, Joshua Lyon Andersen. TNK1 is a ubiquitin sensing kinase that can be targeted in vivo to block tumor growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3489.