Somatic DIS3 mutations in Multiple Myeloma arise early in clonal evolution, but are later counterselected due to toxicity

Abstract

DIS3 encodes an essential ribonucleic subunit of the nuclear exosome complex, responsible for degrading RNA in the nucleus. Somatic DIS3 mutations drive translocations in B cells, leading to multiple myeloma (MM). Clinical data analysis reveals that 42% of DIS3 mutations occur at three recurrent residues (D479, D488, and R780). These mutations, deactivating DIS3 exonucleolytic activity, are never homozygous, often appearing as minor subclones in advanced MM. Surprisingly, mutant DIS3 alleles undergo loss-of-heterozygosity, correlating with frequent del(13q) encompassing DIS3. Overexpression of wild-type DIS3 enhances growth and viability of DIS3-mutated MM cells, while CRISPR-mediated knock-out of the mutant variant, followed by longitudinal co-culture, replicates its elimination through counterselection, observed in the natural course of the disease. In mice, the heterozygous DIS3 D479 mutation is embryolethal, confirming its dominant toxic effects. Transcriptome analysis of patients and cell lines reveals specific transcriptional signatures of DIS3 mutations with accumulation of non-coding unstable RNA species and including secondary indications of decreased proliferation. All these signatures are reversible upon mutant DIS3 loss-of-heterozygosity. DIS3 is an intriguing hit-and-run oncogene that drives MM, but is subsequently eliminated during clonal evolution.