Transposon mutagenesis screen in mice identifies TM9SF2 as a novel colorectal cancer oncogene

Christopher R Clark,Michael B Burns,Juan E Abrahante,Sambhawa Priya,Stefano R Hellweg,Ran Blekhman,Timothy K Starr,Wilaiwan Durose,Juri Habicht,Makayla Maile,Anna Strauss,Patrick Blaney

doi:10.1038/s41598-018-33527-3

Abstract

New therapeutic targets for advanced colorectal cancer (CRC) are critically needed. Our laboratory recently performed an insertional mutagenesis screen in mice to identify novel CRC driver genes and, thus, potential drug targets. Here, we define Transmembrane 9 Superfamily 2 (TM9SF2) as a novel CRC oncogene. TM9SF2 is an understudied protein, belonging to a well conserved protein family characterized by their nine putative transmembrane domains. Based on our transposon screen we found that TM9SF2 is a candidate progression driver in digestive tract tumors. Analysis of The Cancer Genome Atlas (TCGA) data revealed that approximately 35% of CRC patients have elevated levels of TM9SF2 mRNA, data we validated using an independent set of CRC samples. RNAi silencing of TM9SF2 reduced CRC cell growth in an anchorage-independent manner, a hallmark of cancer. Furthermore, CRISPR/Cas9 knockout of TM9SF2 substantially diminished CRC tumor fitness in vitro and in vivo. Transcriptome analysis of TM9SF2 knockout cells revealed a potential role for TM9SF2 in cell cycle progression, oxidative phosphorylation, and ceramide signaling. Lastly, we report that increased TM9SF2 expression correlates with disease stage and low TM9SF2 expression correlate with a more favorable relapse-free survival. Taken together, this study provides evidence that TM9SF2 is a novel CRC oncogene.

Highlights

Colorectal cancer (CRC) arises from a stepwise accumulation of mutations that transform normal epithelia into cancerous tissue[1,2]
In this study we used the Sleeping Beauty (SB) DNA system consisting of an oncogenic DNA transposon (T2/Onc) capable of disrupting tumor suppressor genes and activating oncogenes, which is activated by tissue-specific expression of the SB transposase[20,21,22]
We identified 77 candidate cancer genes whose activity was potentially altered by T2/Onc transposition based on common insertion site (CIS) analysis[23]

Summary

Introduction

Colorectal cancer (CRC) arises from a stepwise accumulation of mutations that transform normal epithelia into cancerous tissue[1,2]. Recent large scale genomic analyses, such as The Cancer Genome Atlas (TCGA), have identified numerous additional recurrent somatic mutations, focal copy number alterations and gene expression changes[3,4]. From these studies it is clear that CRC has a complex genetic etiology. We report our findings on TM9SF2, a transmembrane protein belonging to the transmembrane-9 superfamily (TM9SF), which includes TM9SF1-4 It is well conserved evolutionarily, very little is known about the function of TM9SF proteins in mammalian cells, nor their role in cancer[12,13]. We performed transcriptome analysis to gain insight into the potential role of TM9SF2 as a cell cycle regulating protein

Methods

Results

Conclusion