Abstract 5029: Determining the biological function of TNK1

Abstract Thirty-eight-negative kinase 1 (TNK1) is a poorly characterized member of the ACK family of non-receptor tyrosine kinases, which we recently identified as a driver of cell survival in a subset of primary hematological malignancies. However, the biological function of TNK1 is not well understood. We also found that TNK1 is unusual among kinases for the presence of a functional ubiquitin association (UBA) domain on its C-terminus. We discovered that the TNK1 UBA domain binds to poly-ubiquitin with high affinity and has no apparent preference for ubiquitin chain length or linkage type. Interestingly, the UBA domain is important for TNK1 function, given that deletion of the UBA domain (TNK1 ΔUBA) alters its localization and phospho-substrate network, while also weakening the oncogenic activity of TNK1 in cell transformation assays. Based on these data, we hypothesized that the UBA domain tethers TNK1 to its substrates. To test this hypothesis, we performed quantitative phospho-tyrosine proteomics using murine pro-B cells transformed with either TNK1 full length or TNK1 ΔUBA and identified TANK-binding kinase 1 (TBK1) as a putative UBA-dependent TNK1 substrate. TBK1 is a serine/threonine kinase involved in the regulation of inflammation, autophagy, and NF-ĸB signaling. During the selective autophagic degradation of misfolded proteins (aggrephagy), TBK1 phosphorylates p62 at S403 to increase its affinity to ubiquitin, and thereby increases p62-mediated recruitment of misfolded proteins into the condensate. Unchecked growth of ubiquitin condensates can overwhelm the size capacity of autophagosomes, potentially causing misfolded proteins to become proteotoxic aggregates. Our preliminary data suggest a model in which active TNK1 accumulates at ubiquitin condensates to phosphorylate and inhibit TBK1. Based on these data, we propose that TNK1 acts as a kinase sensor of poly-ubiquitin to control the TBK1-mediated growth of ubiquitin condensates. Citation Format: Emmalee Kohler, Tania Lopez-Palacios, Tsz-Yin Chan, Christina Egbert, Jacob Truman, Spencer Ashworth, Alec Vaughan, Joshua Andersen, D. Madhusanka. Determining the biological function of TNK1. [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 5029.