NOL11, implicated in the pathogenesis of North American Indian Childhood Cirrhosis, is required for pre‐rRNA transcription and processing

Abstract

The R565W mutation in the C‐terminus of the nucleolar ribosome biogenesis factor, hUTP4/Cirhin, causes North American Indian childhood cirrhosis (NAIC). Our objective was to identify non‐conserved interaction partners for hUTP4/Cirhin, as a defective protein‐protein interaction may underlie NAIC. By screening a yeast two‐hybrid cDNA library derived from human liver, and through affinity purification followed by mass spectrometry, we identified an uncharacterized nucleolar protein, NOL11, as an interaction partner for hUTP4/Cirhin. Co‐immunoprecipitation experiments show that NOL11 is a component of the nucleolar human ribosomal small subunit (SSU) processome. siRNA knockdown of NOL11 revealed that it is required to generate the mature 18S rRNA and for optimal rDNA transcription. Yeast two‐hybrid analysis shows that NOL11 interacts with the C‐terminus of hUTP4/Cirhin, and that the R565W mutation partially disrupts this interaction. Expression of the hUTP4/Cirhin R565W mutation only partially rescues the ribosome biogenesis defects, indicating that the disease mutation confers a defect in ribosome biogenesis. We have therefore identified NOL11 as a novel protein required for the nucleolar stages of ribosome biogenesis in humans. Our results further implicate a role for NOL11 in the pathogenesis of NAIC. Supported by NIH GM52581.