Abstract 1895: A conserved E2F1-activated gene regulatory network encompassing monocarboxylic acid transporter-1, its co-operating antisense lncRNA SLC16A1-AS1 and their common downstream targets mediates bladder cancer invasiveness
Authors: Jansen Berdien A. , Logotheti Stella , Heckl Dirk , Klusmann Jan-Henning , Kozcan Dirk , Taher Laila , Fuellen Georg , Engelmann David , Pützer Brigitte 
Published: July 2017

AIM: The therapeutic arsenal against muscle-invasive bladder cancer (BC) is poor, leading to fatal outcomes and necessitating next-generation targeted therapeutics. A causative event of BC progression is activation of the gene regulatory networks (GRN) of the transcription factor E2F1. LncRNAs are emerging integral components of the E2F1-regulated GRNs, but their implication in BC progression is unknown. Our study focuses on lncRNAs that participate in E2F1-activated GRNs underlying BC progression and the therapeutic exploitation thereof.

METHODS: We applied bioinformatics on BC patient cohorts to identify clinically relevant lncRNAs upregulated in invasive stages. Of those, the E2F1-responsive lncRNAs were defined by subjecting T24 clones inducibly overexpressing E2F1 to HTA2.0 RNA arrays. Candidates in close proximity to oncogenes/tumor-suppressors were further selected, based on an emerging “guilt-by-association” rule of lncRNA biology. LncRNAs were qPCR-validated and E2F1-transactivation was shown by ChIP and reporter assays. The SLC16A1-AS1 lncRNA was functionally characterized by CRISPR/Cas9 knockout in invasive BC cells, followed by migration/invasion/metabolic assays, transcriptomics and mice in vivo experimentation. SLC16A1-AS1 homologues across species were predicted by comparative genomics.

RESULTS: Our pipeline unveiled SLC16A1-AS1 lncRNA located nearby and antisense to SLC16A1 protein-coding gene. SLC16A1 synthesizes the membrane-bound Monocarboxylic Acid Transporter-1 (MCT1), a key metabolic regulator that mediates lactate uptake and glycolytic flux and favors BC invasiveness; while SLC16A1-AS1 function was unknown to date. SLC16A1 and SLC16A1-AS1 present a ‘head-to-head’ gene arrangement, with a bidirectional E2F1-responsive promoter. This ‘operon-like’ gene cluster is conserved across mammals, implying functional relevance of MCT1/E2F1/SLC16A1-AS1. In invasive BC cells, E2F1 transactivates SLC16A1-AS1, which remains in the nucleus exerting gene regulatory functions, as well as MCT1, which localizes in the cytoplasm to control lactate flux. SLC16A1-AS1 induces EMT-independent invasiveness by regulating expression of downstream cell migration-related targets which are co-modulated by MCT1.

CONCLUSIONS: MCT1 and SLC16A1-AS1 constitute a composite, E2F1-responsive functional unit, co-operatively regulating common cell-migration related downstream targets. Their conserved gene arrangement, which ensures simultaneous transcription upon E2F1 upregulation, could facilitate co-ordination between metabolism reprogramming and cell migration to establish aggressive phenotypes. Combining SLC16A1-AS1 suppression with formulated MCT1 inhibitors might provide a therapeutic basis against progressive BC.

Citation Format: Berdien A. Jansen, Stella Logotheti, Dirk Heckl, Jan-Henning Klusmann, Dirk Kozcan, Laila Taher, Georg Fuellen, David Engelmann, Brigitte Pützer. A conserved E2F1-activated gene regulatory network encompassing monocarboxylic acid transporter-1, its co-operating antisense lncRNA SLC16A1-AS1 and their common downstream targets mediates bladder cancer invasiveness [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1895. doi:10.1158/1538-7445.AM2017-1895