Promoterless Transposon Mutagenesis Drives Solid Cancers via Tumor Suppressor Inactivation.

Aziz Aiderus,Justin Y Newberg,Karen M Mann,Jerrold M Ward,Amanda L Meshey,Michael B Mann,Ana M Contreras-Sandoval,Deborah A Swing,Nancy A Jenkins,Neal G Copeland

doi:10.3390/cancers13020225

Abstract

Simple SummaryOver the past two decades, there have been many published studies reporting high-copy SB transgenic lines in which the transposon allele includes both gene-trap and internal promoter elements to drive tumorigenesis in vivo. Cancer gene discovery from end-stage solid tumors in these studies performed by our labs and others has found few proto-oncogenic insertions. However, the question remains whether these tumors are initiated by SB insertions in proto-oncogenes to promote permissible phenotypes for tumor initiation, which become dispensable for tumor maintenance. Here, our study expands upon these indirect observations to demonstrate that high-copy SB transposon alleles designed with only gene-trap elements that inactivate genes (Onc2.3) can drive tumor initiation, progression, and maintenance to end-stage tumors in the absence of sensitizing mutations.A central challenge in cancer genomics is the systematic identification of single and cooperating tumor suppressor gene mutations driving cellular transformation and tumor progression in the absence of oncogenic driver mutation(s). Multiple in vitro and in vivo gene inactivation screens have enhanced our understanding of the tumor suppressor gene landscape in various cancers. However, these studies are limited to single or combination gene effects, specific organs, or require sensitizing mutations. In this study, we developed and utilized a Sleeping Beauty transposon mutagenesis system that functions only as a gene trap to exclusively inactivate tumor suppressor genes. Using whole body transposon mobilization in wild type mice, we observed that cumulative gene inactivation can drive tumorigenesis of solid cancers. We provide a quantitative landscape of the tumor suppressor genes inactivated in these cancers and show that, despite the absence of oncogenic drivers, these genes converge on key biological pathways and processes associated with cancer hallmarks.

Highlights

IntroductionRecent genomic analysis of physiologically and histologically normal tissues such as eyelid epidermis and esophageal squamous epithelia show that these tissues tolerate relatively high levels of mutations, typically within known tumor suppressor genes [1,2,3].Sleeping Beauty (SB) insertional mutagenesis [4] is a powerful forward genetic tool used to perform genome-wide forward genetic screens in laboratory mice for cancer gene discovery [5,6,7,8,9,10,11,12,13,14,15]
Using Sleeping Beauty (SB) mutagenesis, we successfully modeled lung alveolar adenoma (LUAA) and adenocarcinoma (LUAC), demonstrating that oncogenic mutant
Rasusing signaling via transposon inactivationsystems, of the negative of in this pathway, the activationRas of oncogenes combination with inactivationsystems, or exclusively absence of oncogenic activation.inTaken together, bytumor usingsuppressor different transposon we show that hepatocellular adenomas (HCA) in mice can be initiated by activation of oncogenes in combination with tumor suppressor inactivation or exclusively by inactivation of cooperating tumor suppressors that converge on similar mechanisms co-opted to promote tumorigenesis

Summary

Introduction

Recent genomic analysis of physiologically and histologically normal tissues such as eyelid epidermis and esophageal squamous epithelia show that these tissues tolerate relatively high levels of mutations, typically within known tumor suppressor genes [1,2,3].Sleeping Beauty (SB) insertional mutagenesis [4] is a powerful forward genetic tool used to perform genome-wide forward genetic screens in laboratory mice for cancer gene discovery [5,6,7,8,9,10,11,12,13,14,15]. We recently conducted and reported an SB screen to model the development of cutaneous squamous cell carcinoma in vivo and noted that approximately 30% of tumors formed without any oncogenic transposon insertions, albeit with extended latency [16,17]. This finding raises two questions: (i) Can exclusive loss of tumor suppressor genes per se drive tumorigenesis? We prioritized solid tumors of the skin, lung and liver and employed highthroughput SBCapSeq approaches [9,11] to identify genome-wide SB mutations and define recurrently mutated, statistically significant candidate cancer drivers (CCDs) from bulk tumors containing more SB mutations expected by chance using the SB Driver Analysis [18]

Methods

Results

Conclusion