Hashem, M. O. | bioRxiv Science

bioRxiv2023

Wiskott-Aldrich Syndrome Protein Regulates Nucleolar Organization and Function in Innate Immune Response

Wiskott-Aldrich syndrome (WAS) is a primary immunodeficiency disorder caused by the dysfunction of the WAS protein (WASP). Using an isogenic macrophage model derived from genome edited induced pluripotent stem cells we demonstrated that WASP functions in the nucleolus, which plays important roles in immune regulation. The absence of WASP resulted in smaller and misshapen nucleoli, decreased fibrillar center territory, and impaired ribosomal RNA (rRNA) transcription. The nucleolar and rRNA phenotypes were confirmed in WAS patient samples. Furthermore, WASP interacts with nucleolar proteins, including nucleophosmin 1 (NPM1) and fibrillarin (FBL). NPM1 deficiency is known to cause elevated cytokine expression following lipopolysaccharide (LPS) stimulation. Consistently, WASP deficient cells displayed lower levels of NPM1 and a heightened inflammatory cytokine response to LPS, which was rescued by overexpressing NPM1. Together, our research provides novel insights into the critical role of WASP in nucleolar function and the modulation of inflammatory cytokine production.

cell biology↗

bioRxiv2019

A missense variant impairing TRMT1 function in tRNA modification is linked to intellectual disability

The human TRMT1 gene encodes a tRNA methyltransferase enzyme responsible for the formation of the dimethylguanosine (m2,2G) modification in cytoplasmic and mitochondrial tRNAs. Frameshift mutations in the TRMT1 gene have been shown to cause autosomal-recessive intellectual disability (ID) in the human population but additional TRMT1 variants remain to be characterized. Moreover, the impact of ID-associated TRMT1 mutations on m2,2G levels in ID-affected patients is unknown. Here, we describe a homozygous missense variant in TRMT1 in a patient displaying developmental delay, ID, and epilepsy. The missense variant changes a conserved arginine residue to a cysteine (R323C) within the methyltransferase domain of TRMT1 and is expected to perturb protein folding. Patient cells expressing the TRMT1-R323C variant exhibit a severe deficiency in m2,2G modifications within tRNAs, indicating that the mutation causes loss-of-function. Notably, the TRMT1 R323C mutant retains the ability to bind tRNA but is unable to rescue m2,2G formation in TRMT1-deficient human cells. Our results identify a pathogenic point mutation in TRMT1 that severely perturbs tRNA modification activity, and provide the first demonstration that m2,2G modifications are disrupted in patients with TRMT1-associated ID disorders.

molecular biology↗