USP9X-mediated deubiquitination of B-cell CLL/lymphoma 9 potentiates Wnt signaling and promotes breast carcinogenesis

Zesen Shang,Jiao Zhao,Qi Zhang,Cheng Cao,Shanshan Tian,Kai Zhang,Ling Liu,Lei Shi,Na Yu,Shangda Yang,Shangda Yang

doi:10.1074/jbc.ra119.007655

Abstract

Hyperactivation of the canonical Wnt-signaling pathway is a prominent feature of a number of human malignancies. Transcriptional activation of this signaling cascade depends on the formation of the β-catenin-B-cell CLL/lymphoma 9 (BCL9)-pygopus (PYGO) family plant homeodomain finger 1 complex, yet how the assembly of this complex is regulated remains to be investigated. Here, using MCF-7, HeLa, HEK293T, MDA-MB-231, and Sf9 cells, along with immunoblotting and immunofluorescence, nano-HPLC-MS/MS, deubiquitination, immunoprecipitation, and chromatin immunoprecipitation (ChIP) assays, we report that BCL9 physically associates with a protein deubiquitinase, ubiquitin-specific peptidase 9, X-linked (USP9X), and that USP9X removes Lys-63-linked polyubiquitin on Lys-212 of BCL9. Importantly, the USP9X-mediated BCL9 deubiquitination facilitated the formation of the β-catenin-BCL9-PYGO complex, thereby potentiating the transcriptional activation of Wnt/β-catenin target genes. We also show that USP9X-mediated BCL9 deubiquitination promotes the proliferation and invasion of breast cancer cells. Together, these results uncover USP9X as a deubiquitinase of BCL9, implicating USP9X in Wnt/β-catenin signaling and breast carcinogenesis.

Highlights

Hyperactivation of the canonical Wnt-signaling pathway is a prominent feature of a number of human malignancies
We showed that USP9X augments the interaction of B-cell lymphoma 9 (BCL9) with ␤-catenin and PYGO1, thereby promoting transcriptional activation of Wnt/ ␤-catenin–responsive genes and the proliferation and invasion of breast cancer cells
We showed that USP9X, in doing so, influences the formation of the ␤-catenin/BCL9/PYGO1 complex and the activation of Wnt/␤-catenin target genes to promote the proliferation and invasion of breast cancer cells (Fig. 7)

Summary

Introduction

Hyperactivation of the canonical Wnt-signaling pathway is a prominent feature of a number of human malignancies Transcriptional activation of this signaling cascade depends on the formation of the ␤-catenin–B-cell CLL/lymphoma 9 (BCL9)– pygopus (PYGO) family plant homeodomain finger 1 complex, yet how the assembly of this complex is regulated remains to be investigated. Activation of Wnt signaling leads to the relief of this repression by blocking the degradation of ␤-catenin, which translocates into the nucleus and converts the Wnt-responsive genes into an active state [2] This de-repression process involves the displacement of the TLE/Groucho complex and the formation of a ␤-catenin–nucleated transcription permissive complex [12,13,14,15,16], in which ␤-catenin, together with PYGO and B-cell lymphoma 9 (BCL9), forms a quaternary complex with TCF/LEF to drive transcriptional activation of Wnt signaling target genes [17,18,19,20].

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Results

Conclusion