A role for the CB-associated SUMO isopeptidase USPL1 in RNAPII-mediated snRNA transcription

Abstract

Cajal bodies are nuclear structures involved in snRNP and snoRNP biogenesis, telomere maintenance and histone mRNA processing. Recently, the SUMO isopeptidase USPL1 was identified as a Cajal body component essential for cellular growth and Cajal body integrity. However, a cellular function for USPL1 is so far unknown. Here, we use RNAi mediated knockdown in human cells in combination with biochemical and fluorescence microscopy approaches to investigate the function of USPL1 and its relation to Cajal bodies. We demonstrate that the levels of RNAPII-transcribed snRNAs are reduced upon knockdown of USPL1 and that downstream processes such as snRNP assembly and pre-mRNA splicing are compromised. Importantly, we find that USPL1 associates directly with U snRNA loci and that it interacts and colocalizes with components of the Little Elongation Complex, which is involved in RNAPII-mediated snRNA transcription. Thus our data indicate that USPL1 plays a key role in the process of RNAPII-mediated snRNA transcription.