Structure, Dynamics, and Functionality of Tankyrase Inhibitor-Induced Degradasomes.

Tankyrase (TNKS) enzymes, due to their poly(ADP-ribose) polymerase activity, have emerged as potential targets in experimental cancer therapy. However, the functional consequences of TNKS inhibition remain incompletely resolved because of the binding promiscuity of TNKS. One of the hallmarks of small-molecule TNKS inhibitors (TNKSi) is the stabilization of AXIN, which plays a pivotal role in the WNT/β-catenin signaling pathway. The present study focused on the known ability of TNKSi to induce cytoplasmic puncta (degradasomes) consisting of components of the signal-limiting WNT/β-catenin destruction complex. Using the colorectal cancer cell line SW480 stably transfected with GFP-TNKS1, it was demonstrated that a TNKS-specific inhibitor (G007-LK) induces highly dynamic and mobile degradasomes that contain phosphorylated β-catenin, ubiquitin, and β-TrCP. Likewise, G007-LK was found to induce similar degradasomes in other colorectal cancer cell lines expressing wild-type or truncated versions of the degradasome component APC. Super-resolution and electron microscopy revealed that the induced degradasomes in SW480 cells are membrane-free structures that consist of a filamentous assembly of high electron densities and discrete subdomains of various destruction complex components. Fluorescence recovery after photobleaching experiments further demonstrated that β-catenin-mCherry was rapidly turned over in the G007-LK-induced degradasomes, whereas GFP-TNKS1 remained stable. In conclusion, TNKS inhibition attenuates WNT/β-catenin signaling by promoting dynamic assemblies of functional active destruction complexes into a TNKS-containing scaffold even in the presence of an APC truncation. This study demonstrates that β-catenin is rapidly turned over in highly dynamic assemblies of WNT destruction complexes (degradasomes) upon tankyrase inhibition and provides a direct mechanistic link between degradasome formation and reduced WNT signaling in colorectal cancer cells.

Thorvaldsen TE ，Pedersen NM ，Wenzel EM ，Schultz SW ，Brech A ，Liestøl K ，Waaler J ，Krauss S ，Stenmark H ... -  《-》

Differential Roles of AXIN1 and AXIN2 in Tankyrase Inhibitor-Induced Formation of Degradasomes and β-Catenin Degradation.

Thorvaldsen TE ，Pedersen NM ，Wenzel EM ，Stenmark H ... -  《PLoS One》

Tankyrase Inhibitors Stimulate the Ability of Tankyrases to Bind Axin and Drive Assembly of β-Catenin Degradation-Competent Axin Puncta.

Martino-Echarri E ，Brocardo MG ，Mills KM ，Henderson BR ... -  《PLoS One》

A novel tankyrase small-molecule inhibitor suppresses APC mutation-driven colorectal tumor growth.

Most colorectal cancers (CRC) are initiated by mutations of APC, leading to increased β-catenin-mediated signaling. However, continued requirement of Wnt/β-catenin signaling for tumor progression in the context of acquired KRAS and other mutations is less well-established. To attenuate Wnt/β-catenin signaling in tumors, we have developed potent and specific small-molecule tankyrase inhibitors, G007-LK and G244-LM, that reduce Wnt/β-catenin signaling by preventing poly(ADP-ribosyl)ation-dependent AXIN degradation, thereby promoting β-catenin destabilization. We show that novel tankyrase inhibitors completely block ligand-driven Wnt/β-catenin signaling in cell culture and display approximately 50% inhibition of APC mutation-driven signaling in most CRC cell lines. It was previously unknown whether the level of AXIN protein stabilization by tankyrase inhibition is sufficient to impact tumor growth in the absence of normal APC activity. Compound G007-LK displays favorable pharmacokinetic properties and inhibits in vivo tumor growth in a subset of APC-mutant CRC xenograft models. In the xenograft model most sensitive to tankyrase inhibitor, COLO-320DM, G007-LK inhibits cell-cycle progression, reduces colony formation, and induces differentiation, suggesting that β-catenin-dependent maintenance of an undifferentiated state may be blocked by tankyrase inhibition. The full potential of the antitumor activity of G007-LK may be limited by intestinal toxicity associated with inhibition of Wnt/β-catenin signaling and cell proliferation in intestinal crypts. These results establish proof-of-concept antitumor efficacy for tankyrase inhibitors in APC-mutant CRC models and uncover potential diagnostic and safety concerns to be overcome as tankyrase inhibitors are advanced into the clinic.

Lau T ，Chan E ，Callow M ，Waaler J ，Boggs J ，Blake RA ，Magnuson S ，Sambrone A ，Schutten M ，Firestein R ，Machon O ，Korinek V ，Choo E ，Diaz D ，Merchant M ，Polakis P ，Holsworth DD ，Krauss S ，Costa M ... -  《-》

Formation of Tankyrase Inhibitor-Induced Degradasomes Requires Proteasome Activity.

Pedersen NM ，Thorvaldsen TE ，Schultz SW ，Wenzel EM ，Stenmark H ... -  《PLoS One》