Tissue-Specific Regulation of the Wnt/β-Catenin Pathway by PAGE4 Inhibition of Tankyrase

Sajjan Koirala,Jonathon Klein,Yumei Zheng,Nicole O Glenn,Travis Eisemann,Klementina Fon Tacer,Darcie J Miller,Ozlem Kulak,Meifen Lu,David B Finkelstein,Geoffrey Neale,Heather Tillman,Peter Vogel,Douglas W Strand,Lawrence Lum,Chad A Brautigam,John M Pascal,Wilson K Clements,Patrick Ryan Potts

doi:10.1016/j.celrep.2020.107922

Abstract

Spatiotemporal control of Wnt/β-catenin signaling is critical for organism development and homeostasis. The poly-(ADP)-ribose polymerase Tankyrase (TNKS1) promotes Wnt/β-catenin signaling through PARylation-mediated degradation of AXIN1, a component of the β-catenin destruction complex. Although Wnt/β-catenin is a niche-restricted signaling program, tissue-specific factors that regulate TNKS1 are not known. Here, we report prostate-associated gene 4 (PAGE4) as a tissue-specific TNKS1 inhibitor that robustly represses canonical Wnt/β-catenin signaling in human cells, zebrafish, and mice. Structural and biochemical studies reveal that PAGE4 acts as an optimal substrate decoy that potently hijacks substrate binding sites on TNKS1 to prevent AXIN1 PARylation and degradation. Consistently, transgenic expression of PAGE4 in mice phenocopies TNKS1 knockout. Physiologically, PAGE4 is selectively expressed in stromal prostate fibroblasts and functions to establish a proper Wnt/β-catenin signaling niche through suppression of autocrine signaling. Our findings reveal a non-canonical mechanism for TNKS1 inhibition that functions to establish tissue-specific control of the Wnt/β-catenin pathway.

Highlights

The Wnt/b-catenin pathway is critical for proper development of all metazoans (Haegel et al, 1995)
Identification of TNKS1 as a prostate-associated gene 4 (PAGE4) Binding Partner To identify the biochemical and cellular function of PAGE4, we carried out an unbiased immunoprecipitation and mass spectrometry (IP-MS) analysis to identify PAGE4 binding partners in HEK293 cells
PAGE4 Prevents PARylation, Ubiquitination, and Degradation of the TNKS1 Substrate AXIN1 To determine whether PAGE4 affects the ability of TNKS1 to PARylate its substrate, we examined whether PAGE4 expression altered PARylation, ubiquitination, and protein levels of AXIN1

Summary

Introduction

The Wnt/b-catenin pathway is critical for proper development of all metazoans (Haegel et al, 1995). Wnt/b-catenin signaling is important in adult organisms, in which it is highly confined to specific organ niches and is critical for the maintenance of stem cell fate, tissue homeostasis, and regeneration (Clevers, 2006; Clevers and Nusse, 2012; Logan and Nusse, 2004; Nusse and Clevers, 2017). The Wnt/b-catenin signaling pathways is a multistep signaling cascade that culminates with the activation of Wnt/ b-catenin target genes. In the ‘‘Wnt-off’’ state, the destruction complex continuously sequesters and degrades b-catenin, whereas in the ‘‘Wnt-on’’ state, b-catenin escapes degradation and translocates into the nucleus to activate target genes (Behrens et al, 1996; Molenaar et al, 1996; Waterman, 2004; Yang et al, 2003)

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