Poster abstracts

Poster number 55 submitted by Lauren Woodward

DNA damage response-induced changes in EJC composition and nucleocytoplasmic mRNA distribution

Lauren Woodward (Department of Molecular Genetics), Justin Mabin (Department of Molecular Genetics ), Guramrit Singh (Department of Molecular Genetics)

Abstract:
The DNA damage response (DDR) is an intracellular signaling network activated to maintain genomic stability. Loss of appropriate DDR response in the face of genomic instability is a characteristic of cancer, and may contribute to reduced therapeutic efficacy. mRNA processing proteins are increasingly being implicated in DDR, including two nuclear SR-like proteins with significant sequence similarity, TRAP150 and BCLAF1. Both proteins are required for survival after DNA damage via poorly understood mechanisms. We recently identified TRAP150 and BCLAF1 as interaction partners of the exon junction complex (EJC). The EJC is a stable core of proteins deposited 24 nt upstream of exon-exon junctions during pre-mRNA splicing. The EJC core serves as a binding platform to which many proteins bind to regulate mRNA fate. TRAP150 and BCLAF1 share a short motif with two well-known EJC partners MLN51 and ALYREF. This motif is required for MLN51- and ALYREF-EJC interaction. Interestingly, these EJC interacting proteins appear to have opposite effects on mRNA nucleocytoplasmic distribution. ALYREF enhances mRNA export. In contrast, TRAP150 causes nuclear RNA retention when tethered to a reporter RNA, and BCLAF1 knockdown causes an increase in cytoplasmic mRNA levels. Strikingly, nuclear mRNA dramatically increases upon DDR induction through unknown mechanisms. We are testing if a change in EJC composition is the driving force behind DDR-induced nuclear mRNA retention. Thus far, we show that TRAP150, BCLAF1, MLN51, and ALYREF associate with EJC in mutually exclusive manner. Furthermore, exposure to UV reduces MLN51 and ALYREF association with the EJC. Fluorescence in situ hybridization analysis shows that TRAP150 knockdown results in increased cytoplasmic polyadenylated transcripts after UV exposure. These results support a model in which UV-induced DNA damage impacts EJC composition to promote nuclear mRNA retention.

Keywords: EJC, DNA Damage Response (DDR), mRNA nuclear retention