Pre-mRNA splicing is the process by which nascent mRNAs join the protein coding sequences,exons, to create mature mRNAs while getting rid of noncoding sequences, known as introns. Duringsplicing, introns are spliced out forming a ‘lariat’- like structure. These lariat RNAs are quickly degradedby RNA debranching enzyme 1 (DBR1), leading to their turnover. Loss of DBR1 gene is embryonicallylethal in humans. Thus, DBR1 is an essential protein in mammalian cells, as it is the only debranchingenzyme that hydrolyzes 2’-5’ bonds during pre-mRNA processing, to promote efficient pre- mRNAsplicing. Our aim to knockdown DBR1 with siRNAs in HEK293 cells resulted in significant accumulationof aberrant splicing products. To further understand if DBR1 is involved in functional coupling betweenpre-mRNA splicing and the mRNA quality control mechanism, nonsense-mediated decay (NMD) whichdegrades transcripts containing premature termination codons (PTCs) to prevent translation of unnecessaryor aberrant transcripts, we asked if DBR1 can be copurified with NMD factors from soluble mammaliancell extracts. Indeed DBR1, in an RNase sensitive manner, coimmunoprecipitated NMD factors UPF1 andCASC3 suggesting its overlapping role in the mRNA surveillance pathway. Further, in-depthcharacterization of DBR1 interactome identified several essential proteins involved in stress granule (SG)assembly and enrichment of specific transcripts in DBR1 depleted cells that are part of the SGtranscriptome. These results demonstrate involvement of DBR1, potentially as a sensor for aberrantlyspliced transcripts and targeting those to a translationally repressed cellular storage foci in mammaliancells.
