A novel protein AXIN1-295aa encoded by circAXIN1 activates the Wnt/\u03b2-catenin signaling pathway to promote gastric cancer progression

Yin Peng,Shanshan Chang,Xiaojing Zhang,Hassan Ashktorab,Yuan Yuan,Duane T Smoot ,Yang Chen,Stephen J Meltzer,Ying Qin,Xiaoshan Feng ,Song Li,Yanjie Wei,Xiaonuan Luo,Kaining Du,Yidan Xu,Xinmin Fan,Fan Hu,Gangqiang Hou,Shiqi Deng,Xiaohui Zhu,Md Tofazzal Hossain ,Zhe Jin

doi:10.1186/s12943-021-01457-w

Abstract

BackgroundCircular RNA (circRNA), a subclass of non-coding RNA, plays a critical role in cancer tumorigenesis and metastasis. It has been suggested that circRNA acts as a microRNA sponge or a scaffold to interact with protein complexes; however, its full range of functions remains elusive. Recently, some circRNAs have been found to have coding potential.MethodsTo investigate the role of circRNAs in gastric cancer (GC), parallel sequencing was performed using five paired GC samples. Differentially expressed circAXIN1 was proposed to encode a novel protein. FLAG-tagged circRNA overexpression plasmid construction, immunoblotting, mass spectrometry, and luciferase reporter analyses were applied to confirm the coding potential of circAXIN1. Gain- and loss-of-function studies were conducted to study the oncogenic role of circAXIN1 and AXIN1-295aa on the proliferation, migration, invasion, and metastasis of GC cells in vitro and in vivo. The competitive interaction between AXIN1-295aa and adenomatous polyposis coli (APC) was investigated by immunoprecipitation analyses. Wnt signaling activity was observed using a Top/Fopflash assay, real-time quantitative RT-PCR, immunoblotting, immunofluorescence staining, and chromatin immunoprecipitation.ResultsCircAXIN1 is highly expressed in GC tissues compared with its expression in paired adjacent normal gastric tissues. CircAXIN1 encodes a 295 amino acid (aa) novel protein, which was named AXIN1-295aa. CircAXIN1 overexpression enhances the cell proliferation, migration, and invasion of GC cells, while the knockdown of circAXIN1 inhibits the malignant behaviors of GC cells in vitro and in vivo. Mechanistically, AXIN1-295aa competitively interacts with APC, leading to dysfunction of the “destruction complex” of the Wnt pathway. Released β-catenin translocates to the nucleus and binds to the TCF consensus site on the promoter, inducing downstream gene expression.ConclusionCircAXIN1 encodes a novel protein, AXIN1-295aa. AXIN1-295aa functions as an oncogenic protein, activating the Wnt signaling pathway to promote GC tumorigenesis and progression, suggesting a potential therapeutic target for GC.

Highlights

Circular RNA, a subclass of non-coding RNA, plays a critical role in cancer tumorigenesis and metastasis
AXIN1-295aa competitively interacts with adenomatous polyposis coli (APC), leading to dysfunction of the “destruction complex” of the Wnt pathway
In this study, based on the high-throughput sequencing results from five paired gastric cancer (GC) samples, we identified the elevated expression of circAXIN1 in GC

Summary

Introduction

Circular RNA (circRNA), a subclass of non-coding RNA, plays a critical role in cancer tumorigenesis and metastasis. It has been suggested that circRNA acts as a microRNA sponge or a scaffold to interact with protein complexes; its full range of functions remains elusive. Some circRNAs have been found to have coding potential. Circular RNAs (circRNAs) are a class of transcripts characterized by a covalently closed loop structure. They have no 5′ to 3′ polarity or polyA tail [1]. CircRNAs are expressed in a tissue-specific, developmental stage-specific, and diseasespecific manner [4]. They are known to act as microRNA sponges, transcription regulators, and scaffolds for mediating protein interactions or localization [5]. Zhang’s group has previously reported that a panel of circRNAs are translated into proteins that function as tumor suppressors in glioblastomas [10]

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