Mirka Uhlirova - A 12

Role of splicing in epithelial homeostasis and tumorigenesis

Pre-mRNA splicing is a critical step in the regulation of gene expression and splicing factors have emerged as gatekeepers of genome stability. Recently, we identified the protein Ecdysoneless (Ecd) as a new component of the splicing machinery that interacts with the core components of the spliceosome and showed its importance for pre-mRNA splicing and cell survival. Intriguingly, Ecd has been found misexpressed or mutated in different types of human cancers. The primary aim of this project is to elucidate the mechanistic principles that underlie Ecd-dependent maintenance of transcriptome, genome and tissue integrity.

Introduction

Proper gene expression in eukaryotes requires precise excision of introns and fusion of exons. This multi-step reaction is catalyzed by a multiprotein/RNA complex - the spliceosome. The pre-mRNA splicing occurs co-transcriptionally and is among the first steps towards maturation of the mRNA molecule. The spliceosome consists of five small nuclear ribonucleoprotein particles (snRNP) and more than a hundred proteins that dynamically associate with the complex. Accuracy and tight regulation of this machinery must be maintained at all times, as aberrant RNA splicing has detrimental consequences for cell and tissue functions. Importantly, mutations or dysregulation of specific splicing factors have been linked to tumor development and progression. Moreover, mounting evidence shows that cancer cells often display “spliceosome addiction” to maintain high metabolic activity. The spliceosome thus represents a key machine supporting tumorigenesis but also a potential Achilles’ heel of tumor cells, manipulation of which might be exploited to combat cancer.

The contribution of spliceosome malfunction to tumorigenesis is manifold, including aberrant processing of transcripts encoding proteins required for the maintenance of cell and tissue homeostasis or generating cancer specific mRNAs. However, splicing factor dysregulation can also promote genome instability. 

Ecd is a novel splicing factor that interacts with components of the U5 snRNP 

Recent work from our lab identified a new role for the evolutionarily conserved protein Ecd in pre-mRNA splicing. We showed that Ecd interacts with the core components of the U5 snRNP, including Aar2 and Prp8, and its loss results in splicing errors in Drosophila. We further demonstrated that mitotically active rather than differentiated cells are highly sensitive to Ecd deficiency. Importantly, the expression of human Ecd rescues the cellular and molecular defects caused by loss of the Drosophila ortholog. Intriguingly, Ecd has been found upregulated or mutated in various human cancer types. Consistently, we showed the requirement of Ecd for survival and progression of the hyperplastic lesions induced by oncogenic Ras in Drosophila imaginal tissue. Given its predominantly cytoplasmic localization, we hypothesize that Ecd is necessary for the formation of U5 snRNPs which are later incorporated into assembling spliceosomes in the nucleus. Ecd malfunction on the other hand impacts U5 snRNP biogenesis, causing spliceosome scarcity which results in splicing aberrations and genome instability. The primary objective of our project is to unravel the role of Ecd in snRNP biogenesis and its function in the maintenance of tissue homeostasis and tumorigenesis. We are particularly interested in identifying the genetic network that links aberrant splicing to genome instability, the mechanisms that underlie differential cell and transcript sensitivity to Ecd deficiency and defining the pathogenicity of tumor-associated Ecd mutations and the role of Ecd in skin homeostasis and tumorigenesis. To address the standing questions, we combine Omic technologies with forward and reverse genetics in the Drosophila and mouse models. 

Perspectives

The frequent alterations of splicing factors in various human cancers indicate that targeting the spliceosome might be a viable therapeutic option. Indeed, several compounds have shown marked anti-tumor effects and entered clinical trials. Better understanding the role of individual splicing regulators in physiological and disease contexts is crucial for the development of new splicing modulators and inhibitors which can be used as effective next generation anti-cancer drugs.

Selected publications

Claudius, A. K., Romani, P., Lamkemeyer, T., Jindra, M. & Uhlirova, M. (2014). Unexpected Role of the Steroid-Deficiency Protein Ecdysoneless in Pre-mRNA Splicing. PLoS Genetics 1 e1004287.

Martinez Carrera LA, Gabriel E, Donohoe CD, Hölker I, Mariappan A, Storbeck M, Uhlirova, M., Gopalakrishnan J, Wirth B. (2018) Novel insights into SMALED2: BICD2 mutations increase microtubule stability and cause defects in axonal and NMJ development. Human Molecular Genetics, 10:1772-1784.


Prof. Dr. Mirka Uhlirova

Institute for Genetics and CECAD Cologne / RG location - CECAD Building

Prof. Dr. Mirka Uhlirova

Principal Investigator A 12

Mirka.Uhlirova@uni-koeln.de

Work +49 221 478 84334

CECAD Research Center
Joseph-Stelzmann-Str. 26
50931 Cologne

Publications - Mirka Uhlirova

Link to PubMed

Group Members

Gábor Csordás (PostDoc)
Steffen Erkelenz (PostDoc)
Juliane Mundorf (PostDoc)
Eva Külshammer (Lab manager)
Andreia Correia (doctoral student)
Tina Bresser (technician)
Dimitrije Stanković (doctoral student)

Figure 1

CMMC Uhlirova
Fig. 1: Ecd deficiency in imaginal cells (green) induces massive apoptosis (Dcp1). While cell death can be suppressed cell-autonomously by an overexpression of the pan-Caspase inhibitor p35, the apoptosis rate dramatically increases in the surrounding wild-type tissue.

Figure 2

CMMC Uhlirova
Fig. 2: Depletion of Ecd or Prp8 in epithelial cells of the wing imaginal discs (green) induces antioxidant and detoxification response manifested by the increase of the gstD1-GFP reporter activity.