Ubiquitination of the spliceosome auxiliary factor hnRNPA1 by TRAF6 links chronic innate immune signaling with hematopoietic defects and myelodysplasia. Mus musculus

Toll-like receptors (TLR) activation contributes to premalignant hematologic conditions, such as myelodysplastic syndromes (MDS). TRAF6, a TLR effector with ubiquitin (Ub) ligase activity, is overexpressed in MDS hematopoietic stem/progenitor cells (HSPCs). We found that TRAF6 overexpression in mouse HSPC results in impaired hematopoiesis and bone marrow failure. Using a global Ub screen, we identified hnRNPA1, an RNA-binding protein and auxiliary splicing factor, as a substrate of TRAF6. TRAF6 ubiquitination of hnRNPA1 regulated alternative splicing of Arhgap1, which resulted in activation of the GTP-binding Rho family protein Cdc42 and accounted for hematopoietic defects in TRAF6-expressing HSPCs. These results implicate Ub signaling in coordinating RNA processing by TLR pathways during an immune response and in premalignant hematologic diseases, such as MDS. Overall design: Lineage negative and Sca-1 and c-Kit copositive cells (LSK) that are enriched in hematopoietic stem and progenitor cells (HSPC) were isolated from three TRAF6 transgenic mice (03, 04, 05) and four control littermates (21, 22, 23, 24). RNA was reverse transcribed and labeled, and hybridized onto the GeneChip® Mouse Exon 1.0 ST Arrays. A total of 7 samples were included, and two groups are assigned based on genotype. Comparison comprises mRNA expression profile of TRAF6 transgenic group v.s. wild type group. Exon usage patterns are determined by FIRMA Index with AltAnalyze software.