Competitive binding of E3 ligases TRIM26 and WWP2 controls SOX2 in glioblastoma

Tatenda Mahlokozera,Afshin Salehi,Amit D Gujar,Xuan Qu,Rukayat Taiwo,Daniel Hafez,Hiroko Yano,Albert H Kim,Diane D Mao,Hao Chen,Allegra A Petti,Gavin P Dunn,Nima Mosammaparast,Bhuvic Patel,Wei Yang,Mounica Paturu,Patrick Desouza

doi:10.1038/s41467-021-26653-6

Tatenda Mahlokozera, Afshin Salehi + Show 15 more

Open Access

https://doi.org/10.1038/s41467-021-26653-6

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Abstract

The pluripotency transcription factor SOX2 is essential for the maintenance of glioblastoma stem cells (GSC), which are thought to underlie tumor growth, treatment resistance, and recurrence. To understand how SOX2 is regulated in GSCs, we utilized a proteomic approach and identified the E3 ubiquitin ligase TRIM26 as a direct SOX2-interacting protein. Unexpectedly, we found TRIM26 depletion decreased SOX2 protein levels and increased SOX2 polyubiquitination in patient-derived GSCs, suggesting TRIM26 promotes SOX2 protein stability. Accordingly, TRIM26 knockdown disrupted the SOX2 gene network and inhibited both self-renewal capacity as well as in vivo tumorigenicity in multiple GSC lines. Mechanistically, we found TRIM26, via its C-terminal PRYSPRY domain, but independent of its RING domain, stabilizes SOX2 protein by directly inhibiting the interaction of SOX2 with WWP2, which we identify as a bona fide SOX2 E3 ligase in GSCs. Our work identifies E3 ligase competition as a critical mechanism of SOX2 regulation, with functional consequences for GSC identity and maintenance.

Highlights

The pluripotency transcription factor SOX2 is essential for the maintenance of glioblastoma stem cells (GSC), which are thought to underlie tumor growth, treatment resistance, and recurrence
Using the WWP2 RNA interference (RNAi) validated by cDNA-specific rescue (Supplementary Fig. 5C), we found that WWP2 knockdown increased GSC self-renewal capacity in two different GSC lines (Fig. 4F), consistent with WWP2’s role as an E3 ubiquitin ligase that targets SOX2 protein for proteasomal degradation
In the context of GSCs, the TRIM26 RNAi-induced decrease in SOX2 protein could be reversed by simultaneous WWP2 knockdown in two distinct GSC lines (Fig. 5F). Consistent with this biochemical result, we found that the TRIM26 knockdown-induced inhibition of self-renewal could be reversed by WWP2 knockdown in GSCs (Fig. 5G). These results indicate that WWP2 is a bona fide SOX2-directed E3 ubiquitin ligase in GSCs and that TRIM26 directly disrupts WWP2-SOX2 binding and SOX2 polyubiquitination, leading to the maintenance of SOX2 protein levels and GSC biologic phenotypes

Summary

Introduction

The pluripotency transcription factor SOX2 is essential for the maintenance of glioblastoma stem cells (GSC), which are thought to underlie tumor growth, treatment resistance, and recurrence. We identify WWP2 as a bona fide E3 ubiquitin ligase that targets SOX2 for proteasomal degradation in GSCs in vitro and glioblastoma cells in vivo. We elucidate the mechanism by which SOX2 is protected by TRIM26, which competes with WWP2 for binding to SOX2, resulting in inhibition of WWP2-mediated SOX2 polyubiquitination and subsequent proteasomal degradation. These results highlight that regulation of SOX2 at the posttranslational level is essential for the maintenance of GSC identity and biologic phenotypes

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